Check of number of elements in parameter packs and type will be done later. I had no idea this technique had a name and a Wikipedia page! I can't think of another way to iterate over the var-args of a macro, since I don't know how to do anything to the text of each var-arg element. 2 or more template parameters: The number of template parameter will define the number of single disks of the Odometer. rev2023.6.2.43474. Iterate over 2 template parameter packs in parallel, Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. Does the Fool say "There is no God" or "No to God" in Psalm 14:1. Should I trust my own thoughts when studying philosophy? This has the advantage of not needing a second overload, but has the disadvantage of less than stellar readability: For an explanation of how this works, see T.Cs excellent answer. I also clearly tagged it as C++14, not C++17. Now, I want to add a variadic constructor, where I can add whatever data. I'm not claiming it's a good or generally useful answer! I see three ways to acomplish this as the code below illustrates. Have a question or improvement idea? Variadic recursive preprocessor macros - is it possible? Other tasks are a bit trickier to accomplish, such as iterating // return ((true && true) && true) && false; // return (args + + 1 * 2); // Error: operator with precedence below cast, https://en.cppreference.com/mwiki/index.php?title=cpp/language/fold&oldid=148410, an expression that contains an unexpanded, an expression that does not contain an unexpanded, the expansion results of fold expressions were not enclosed with parentheses. and only applies if the structure is yours and you are willing to clutter (imho) its definition. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Note that the opening and closing parentheses are a required part of the fold expression. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Lets say I want to be able to take every string argument and append an exclamation mark before printing it out on a new line. Does a knockout punch always carry the risk of killing the receiver? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Reduces (folds) a parameter pack over a binary operator. In C++20 you can just define template lambda inside the function to do this. Both parameter pack expansion and the "variadic" ellipsis may appear in the declaration of a function template, as in the case of This page was last modified on 21 February 2023, at 11:45. (I know it does not make sense to repeat an item 1 times ;)). Is Spider-Man the only Marvel character that has been represented as multiple non-human characters? As you can see, one doesn't even need a class here. WebSometimes you want to iterate over a parameter pack until some condition holds. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Ways to find a safe route on flooded roads. I got really interested in this problem. How to iterate over Variadic template types (not arguments)? Use of Stein's maximal principle in Bourgain's paper on Besicovitch sets, Citing my unpublished master's thesis in the article that builds on top of it. Insufficient travel insurance to cover the massive medical expenses for a visitor to US? WebThe simplest solution is to recurse: void print_all(std::ostream& os) { // base case } template void print_all(std::ostream& os, T const& first, Ts const& rest) { How to iterate over a parameter pack and switch on parameter type? By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. "I don't like it when it is rainy." It's possible to write a helper function to iterate over a parameter pack: // Invoke each of the functions `f` in sequence template void still, the use of this array means 2 things: all the arguments passed through the variable argument list need to be of the same type (in your case. First of all, to be logically correct, the condition should read Index < TotalSize - 1., as tuple element counts are zero-based. Asking for help, clarification, or responding to other answers. Execution and expansion are not the same thing. How to make a HUE colour node with cycling colours. I thought I could do this using sizeof(Args) as follows: This doesn't compile because std::get(args) requires i to be a compile time constant. In GraphQL, how to control DB query by client query? How can I divide the contour in three parts with the same arclength? Would the presence of superhumans necessarily lead to giving them authority? Use of Stein's maximal principle in Bourgain's paper on Besicovitch sets. So in order to conditionally compile the if-branch only when the condition is fulfilled, you would have to use if constexpr(Index < TotalSize - 1) (see on godbolt). Connect and share knowledge within a single location that is structured and easy to search. Furthermore, even if Index == TotalSize - 1, the compiler is still forced to instantiate ParseCompositeFields (as it has to compile the if-branch), which effectively is ParseCompositeFields. For C++14, you have to fall back on using template specializations and function objects: Thanks for contributing an answer to Stack Overflow! And, as an extension, even the data type of values on each of the single disks could be different. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. What happens if you've already found the item an old map leads to? Is linked content still subject to the CC-BY-SA license? https://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html. Why is Bb8 better than Bc7 in this position? WebReduces ( folds) a parameter pack over a binary operator. Can I trust my bikes frame after I was hit by a car if there's no visible cracking? I had stumbled upon the, I've seen how the double-stringize works in, Henk > in fact i don't remember why, it's been in my codebase for ages. Movie in which a group of friends are driven to an abandoned warehouse full of vampires. variadic macro that handles last argument in a different way. You need either. One problem might arise if the order of invocation matters. VS "I don't like it raining.". Asking for help, clarification, or responding to other answers. 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. I think we don't need recursion here. Does the policy change for AI-generated content affect users who (want to) recursive variadic template to print out the contents of a parameter pack, Iterating a parameter pack with variadic templates in c++. Not the answer you're looking for? Why are mountain bike tires rated for so much lower pressure than road bikes? By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Connect and share knowledge within a single location that is structured and easy to search. Call a common named method of all base classes from a derived class with multiple inheritance. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The other macros are for convenience when converting to common collections. How to use Variadic Function with strings, without using templates? But I had two minor problems with it: Compiling with the pedantic option I got the warning: "ISO99 requires rest arguments to be used". You seem to be using rather old technique here. How can I manually analyse this simple BJT circuit? First story of aliens pretending to be humans especially a "human" family (like Coneheads) that is trying to fit in, maybe for a long time? Does the policy change for AI-generated content affect users who (want to) GraphQL: How to restrict fields server-side across queries? Why does bunched up aluminum foil become so extremely hard to compress? EDIT: These days (c++17), I'd do it like this: What Xeo said. For example: Use a parameter pack with a fold expression: Here is an iterative solution. Which fighter jet is this, based on the silhouette? 1) either it was needed by some creepy compiler 2) either it's a mistake from my part :), it surely has to do with old code warrior compiler or msvc++ 6. C++17 Iterate over a subset of parameter pack. Anyway, the following sample code works up to 8 fields for the sake of clarity. Which fighter jet is this, based on the silhouette? Can you please show how to do this without recursion? This does not work for the use case, where I want 1 template parameter like. I'm sorry but I fail to see how this snippet answers the question. How can I define top vertical gap for wrapfigure? How am I going to get the index in. How common is it to take off from a taxiway? The number of template parameters defines the behavior of the class. Just removing the x parameter from the FOR_EACH macro. Im waiting for my US passport (am a dual citizen. donnez-moi or me donner? Often, we need to perform an operation over every element in a variadic template parameter pack. Not the answer you're looking for? Which comes first: CI/CD or microservices? How to iterate over a parameter pack and switch on parameter type? Find centralized, trusted content and collaborate around the technologies you use most. instantiation 'std::tuple_element<3,std::tuple>' being compiled. C++11 indexing template parameter packs at runtime in order to access Nth type, How do I get index of elements in parameter pack. std::index_sequence, but I do not know. Does substituting electrons with muons change the atomic shell configuration? I do not want to use recursive templates. How does one show in IPA that the first sound in "get" and "got" is different? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Is linked content still subject to the CC-BY-SA license? It's not. Note: this is different from a function parameter pack expansion, which is indicated by an ellipsis that is a part of a parameter declarator, rather than an ellipsis that appears after all parameter declarations. Something like this: But you can also iterate with recursion, which might be easier in your case: Thanks for contributing an answer to Stack Overflow! Im waiting for my US passport (am a dual citizen. I'm currently trying to implement a function, which accepts some data and a parameter-pack args. For e.g. I'm trying to write a variadic template function that includes a loop that iterates over each type in the parameter pack. Can you check my solution? To learn more, see our tips on writing great answers. I can't think of another way to iterate over the var-args of a macro, since I don't know how to do anything to the text of each var-arg element. I'm using this to build up a tuple which I then apply on the callback function which determined the template types. The simplest solution is to recurse: We could instead use the expander trick, to perform all the streaming in a single function. Recursive iteration over parameter pack. Theoretical Approaches to crack large files encrypted with AES. KSVarArgs is a set of macros designed to make dealing with variable arguments easier in Objective-C. All macros assume that the varargs list contains only objective-c objects or object-like structures (assignable to type id). How can I iterate over variadic template parameters in c++? 2 Answers. Getting the size of each type of the parameter pack? Insufficient travel insurance to cover the massive medical expenses for a visitor to US? How to print a variable number of parameters with a macro? What is this object inside my bathtub drain that is causing a blockage? But here's my idea for iterating over var-args: This is the best I can think of, with standard C: I'm adding this as another answer. How can an accidental cat scratch break skin but not damage clothes? 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. How appropriate is it to post a tweet saying that I am looking for postdoc positions? 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. In the case of. The first is a fold-expression: And the second is if constexpr, which allows us to write our original recursive solution in a single function: Found a mistake? How, exactly, does the double-stringize trick work? Just remove it. "); } // Modify multiple strings. I have a function that takes in a parameter pack of vectors, These vectors will be of the same length, and I want to call a function with the values of both of these vectors at each index. Is there a reliable way to check if a trigger being fired was the result of a DML action from another *specific* trigger? Also a very good answer! Is it possible to type a single quote/paren/etc. I'm using this to build up a tuple which I then apply on the callback function which determined the template types. when you have Vim mapped to always print two? To use a std::tuple to iterate over a parameter pack, you would usually use a std::index_sequence to introduce a new pack of indices, and use a fold expression to do the actual iteration. Should I include non-technical degree and non-engineering experience in my software engineer CV? As pretty as it was. This won't work because i is not a constant expression. WebOften, we need to perform an operation over every element in a variadic template parameter pack. Since i used it in a very generic way, i sometimes had to call the repeat macro with only 1 argument. However, lambdas allow you to capture variables like: To enable for an empty __VA_ARGS__, one can use the GNU extension ##_VA_ARGS__ iterate in variadic templates without parameters, Iterate over base classes and variadic parameter list, Variadic template class iterate over types. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. How much of the power drawn by a chip turns into heat? My father is ill and booked a flight to see him - can I travel on my other passport? 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. Asking for help, clarification, or responding to other answers. Insufficient travel insurance to cover the massive medical expenses for a visitor to US? EDIT: Here is a slightly different version that tries to be more generic. I started to implement a very flexible Odometer. Not the answer you're looking for? How common is it to take off from a taxiway? My father is ill and booked a flight to see him - can I travel on my other passport? rev2023.6.2.43474. How could a person make a concoction smooth enough to drink and inject without access to a blender? which one to use in this conversation? I could also use std::apply. What could I do? C puzzleHow Can I pass variadic arguments into a macro? First story of aliens pretending to be humans especially a "human" family (like Coneheads) that is trying to fit in, maybe for a long time? Iterating over a parameter pack of structured templates. \main.cpp(56): note: see reference to class template Applications of maximal surfaces in Lorentz spaces. In the case of Odometer, this will result in a data type std::tuple, std::vector, std::vector>. Is there a reason beyond protection from potential corruption to restrict a minister's ability to personally relieve and appoint civil servants? Insufficient travel insurance to cover the massive medical expenses for a visitor to US? Asking for help, clarification, or responding to other answers. Is it possible to convert a C string literal to uppercase using the preprocessor (macros)? Why is it "Gaudeamus igitur, *iuvenes dum* sumus!" rev2023.6.2.43474. How can I do a recursion on C++ variadic templates? Apparently the compiler keeps trying to compile the recursive function, but not the overload to stop the recursion. But here's my idea for iterating over var-args: Then you can expand both packs in one for the general case, and you only have one pack for the special case. What happens if you've already found the item an old map leads to? Is there a way to make this work? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Your parameter pack is not decreasing, but index is increasing. Citing my unpublished master's thesis in the article that builds on top of it. I'm asking because I want to define a function/api that converts a list of strings into a single comma separated string. How can I iterate over a packed variadic template argument list? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Thanks for contributing an answer to Stack Overflow! Find centralized, trusted content and collaborate around the technologies you use most. Why shouldnt I be a skeptic about the Necessitation Rule for alethic modal logics? To create a context for pack expansion I used the argument list of a function that does nothing (dummy): As an example, suppose you want to display each A::var. Of course there are exceptions though. There are many ways to do this, and the solutions get easier to read Insufficient travel insurance to cover the massive medical expenses for a visitor to US? The FOR_EACH(what, ) macro applies what to every other argument in the variable argument list. In general relativity, why is Earth able to accelerate? The array could potentially be a C99 anonymous array. Not the answer you're looking for? mean? Something like this: template // Modify single string. Is it possible to iterate over arguments in variadic macros? It has one issue: the order in which the elements are processed is not specified by the standard. Why does the bool tool remove entire object? Is graphql schema circular reference an anti-pattern? It may have several disks with even different amount of values on each different disk. Thanks for contributing an answer to Stack Overflow! First the code misses a definition of. To attain moksha, must you be born as a Hindu? Find centralized, trusted content and collaborate around the technologies you use most. There is a bit of noise in the function call, but no computation of the number of varargs is needed. donnez-moi or me donner? Is there a reliable way to check if a trigger being fired was the result of a DML action from another *specific* trigger? GraphQL: How to Prevent Database Scraping? The solution of Gregory Pakosz worked great. No I need to think on what to use . @Jodocus, is our solutions give the same result? How much of the power drawn by a chip turns into heat? How can I iterate over variadic template parameters in c++? Connect and share knowledge within a single location that is structured and easy to search. IIRC, before C++17 this doesn't have strong evaluation order, so it might fail you sometimes. Here is my homework of the day, it's based on macro tricks and today I particularly learnt about __VA_NARG__ invented by Laurent Deniau. Korbanot only at Beis Hamikdash ? To learn more, see our tips on writing great answers. What happens if you've already found the item an old map leads to? which one to use in this conversation? iterating over variadic template's type parameters, Iterating a parameter pack with variadic templates in c++. rev2023.6.2.43474. In July 2022, did China have more nuclear weapons than Domino's Pizza locations? So, I need to iterate of 2 parameter packs in parallel at the same time. After expansion is completed, use iterators to determine the index. Don't have to recite korbanot at mincha? This however will lead to the error your got when trying to instantiate std::get. Removing those and changing the call to FOR_EACH_1 in FOR_EACH_2 removed this warning. Because you are handling the case where Ts is a pack of one differently, it would be sensible to make that a specialisation. The way to go is to move the code from the lambda's args to code: Thanks for contributing an answer to Stack Overflow! Obviously you need to adjust the macro to fit your situation. Thanks for contributing an answer to Stack Overflow! How can I divide the contour in three parts with the same arclength? Hydrogen Isotopes and Bronsted Lowry Acid. Yes, there are major limitations to this. Is there a reliable way to check if a trigger being fired was the result of a DML action from another *specific* trigger? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, That's a really strange requirement. How to disable Hasura schema introspection? Think deeper. But the advantage is that when you have to add a new field to the structure, you only have one place to modify, the X_FIELDS macro. It's an alternative for those using C++11 and willing to avoid macros. rather than "Gaudeamus igitur, *dum iuvenes* sumus!"? Suppose we simply want to print every element in a pack. The only idea I have now is to use a helper class with a std::index_sequence, but I do not know. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, How to iterate over the size of a parameter pack with a compile-time index parameter, Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. In general relativity, why is Earth able to accelerate? Colour composition of Bromine during diffusion? rev2023.6.2.43474. This is really a great answer. Can I trust my bikes frame after I was hit by a car if there's no visible cracking? Is it possible to type a single quote/paren/etc. authenticate user and serve only their related data. There are many ways to do this, and the solutions get easier to read and write with C++17. mean? The best way is to use parameters pack. Which fighter jet is this, based on the silhouette? sizeof(array)/sizeof(array[0]). Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. Iterating over types in a variadic template. Asking for help, clarification, or responding to other answers. What if the numbers and words I wrote on my check don't match? Is there anything called Shallow Learning? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Is there any evidence suggesting or refuting that Russian officials knowingly lied that Russia was not going to attack Ukraine? How to make a variadic macro (variable number of arguments). Each disk has the data type of the template parameter. This page has been accessed 496,016 times. // within all(), the unary left fold expands as. That's the problem. Do we decide the output of a sequental circuit based on its present state or next state? I'd be tempted to split that out into a separate class, so that you didn't have to deal with a parameter pack. To use a std::tuple to iterate over a parameter pack, you would usually use a std::index_sequence to introduce a new pack of indices, and use a fold expression to do the actual iteration. How common is it to take off from a taxiway? Lambda 101: [ capture ] ( params ) { code } ( args to call "in-place" ); If you want to expand a lambda with a variadic template, it won't work as mentioned above when the parameters is of a non-trivial type: Is it the right and the only way to iterate over a parameter pack with std::tuple? To learn more, see our tips on writing great answers. The answers above work -- here I explore a bit more on using a lambda for complex use cases. Connect and share knowledge within a single location that is structured and easy to search. 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. Each disk has the data type of the template parameter. Thanks for catching the missing [], though. Applications of maximal surfaces in Lorentz spaces. Is it possible to handle each element in a variadic macro at compile time in C? Template parameter pack (appears in alias template, class template, variable template (since C++14) and function How to iterate over Variadic template types (not arguments)? donnez-moi or me donner? I just used this approach in a case in which I wanted to have an enum and have access to the enum elements by name. Creating intermediate structs will also enforce evaluation order. What does Bell mean by polarization of spin state? https://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html, https://stackoverflow.com/a/11994395/1938348, Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. I omit the check for the moment and will add it later. Of course, you can do this with recursion, simply ending the recursion when you hit the stop Ways to find a safe route on flooded roads. void foo(std::string& arg) { arg.append("! Is variadic macro subsitution for every argument possible? Is there anything called Shallow Learning? The instantiation of a fold expression expands the expression e as follows: (where N is the number of elements in the pack expansion). Recursive template parameter pack programming. . The only idea I have now is to use a helper class with a How can I shave a sheet of plywood into a wedge shim? Movie in which a group of friends are driven to an abandoned warehouse full of vampires. Aside from humanoid, what other body builds would be viable for an (intelligence wise) human-like sentient species? To learn more, see our tips on writing great answers. You could make the type one of the macro params. Is there any evidence suggesting or refuting that Russian officials knowingly lied that Russia was not going to attack Ukraine? What if the numbers and words I wrote on my check don't match? So, I have the parameter pack off the class and the parameter pack of the constructor. and it seems like a stringstream with a loop is the most efficient way. Take them as a parameter pack. You don't need recursion. This is similar to one of my suggestions. Why does the bool tool remove entire object? First story of aliens pretending to be humans especially a "human" family (like Coneheads) that is trying to fit in, maybe for a long time? Does the policy change for AI-generated content affect users who (want to) How can I iterate over a packed variadic template argument list? Don't have to recite korbanot at mincha? Thanks for contributing an answer to Stack Overflow! Making statements based on opinion; back them up with references or personal experience. This is caused by the variad arguments in the first FOR_EACH_1 macro. Ways to find a safe route on flooded roads. I can't use Boost.MPL. Don't Repeat yourself! Let's assume that the parameter pack will never have a size smaller than 3. You can use template lambda to expand index_sequence and get the corresponding tuple elements through std::get: You don't need to iterate manually, you just need a function to convert each argument into vector: and then your constructor is simply (Should be more complicated: SFINAE for nearly copy constructor with forwarding reference to avoid current copies): Notice that as_vector(args) uses both packs with a single , so they should have same size. Who cares if there are arguments? You can define a helper function to use index_sequence to expand the elements of Tuple and assign values through fold expression. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Neat. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. @Blacktempel, I got the solution working with index thing. Noise cancels but variance sums - contradiction? However, all the information is available at compile time. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. 2 or more template parameters: The number of template parameter will define the number of single disks of the Odometer. Does the policy change for AI-generated content affect users who (want to) How to make generic computations over heterogeneous argument packs of a variadic template function? Iterating over vectors in a parameter pack. The caller of the function makes sure that the size of Args must be even, such as 2, 4, 6 And my function will pass them two by two to two functions. It indeed obfuscates the code but makes the final user experience better and without constraints. Is there a reason beyond protection from potential corruption to restrict a minister's ability to personally relieve and appoint civil servants? Why are mountain bike tires rated for so much lower pressure than road bikes? Movie in which a group of friends are driven to an abandoned warehouse full of vampires. Making statements based on opinion; back them up with references or personal experience. Generally when dealing with variadics: Create a context where pack expansion can be used, isolate what you want to do into a function. if rest is empty, there will be no call to. How to fill array with contents of a template parameter pack? You should be able create function overloads for calling lua_push and use a fold expression instead of the loop. @user1095108: If the pack is empty, you'd get a zero-sized array, which is ill-formed. Is there liablility if Alice scares Bob and Bob damages something? create structs, dont execute anything. Why do some images depict the same constellations differently? I was wondering whether it would be possible to split up a, That's a nice trick Gregory. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. @Blacktempel If this is clear to you, why do you ask then? Which fighter jet is this, based on the silhouette? The answers above work -- here I explore a bit more on using a lambda for complex use cases. Is it OK to pray any five decades of the Rosary or do they have to be in the specific set of mysteries? Why do you need index anyway? To learn more, see our tips on writing great answers. rev2023.6.2.43474. template void print (T value) { std::cout << value << std::endl; Syntax 1) unary right fold 2) unary left fold 3) binary right fold 4) binary left fold Note that the opening and closing By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. How to use SWIG to wrap std::function objects? In Europe, do trains/buses get transported by ferries with the passengers inside? When a unary fold is used with a pack expansion of length zero, only the following operators are allowed: If the expression used as init or as pack has an operator with precedence below cast at the top level, it must be parenthesized: The following behavior-changing defect reports were applied retroactively to previously published C++ standards. In that case, I suppose, one could add a comma and 0, i.e. This is about expanding variadics, works the same. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. However, with this approach, all the parameters you pass to the lambda expression need to have the same type, int in the example above. What does "Welcome to SeaWorld, kid!" So, you just have to define a macro that takes a single argument like this: which is going to be applied to every argument in the list. To learn more, see our tips on writing great answers. \utility(446): error C2338: tuple index out of bounds How does TeX know whether to eat this space if its catcode is about to change? Find centralized, trusted content and collaborate around the technologies you use most. I need to define a function with template parameter pack with C++14. Inside I call another function, which recursively iterates the given arguments. It may be the best you can do in C99 / GNU C, though. Of course types and number of arguments must match. This is clear to me. Why wouldn't a plane start its take-off run from the very beginning of the runway to keep the option to utilize the full runway if necessary? To attain moksha, must you be born as a Hindu? Just extend the code by duplicating if you need more (this is because the preprocessor doesn't feature recursion, as it reads the file only once). Connect and share knowledge within a single location that is structured and easy to search. Noise cancels but variance sums - contradiction? Living room light switches do not work during warm/hot weather. 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. Connect and share knowledge within a single location that is structured and easy to search. Find centralized, trusted content and collaborate around the technologies you use most. Please see the below code example for an illustration of the problem (I deleted most of the code in the class, to just show you the problem): I can iterate over the parameter pack of the constructor using a fold expression. I was wondering if it is possible to iterate over arguments passed to a variadic macro in C99 or using any GCC extensions ? By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Citing my unpublished master's thesis in the article that builds on top of it. The base macro ksva_iterate_list() iterates over the variable arguments, invoking a block for each argument, until it encounters a terminating nil. Living room light switches do not work during warm/hot weather, Citing my unpublished master's thesis in the article that builds on top of it. How to extract a value from a variadic template parameter pack by index? Find centralized, trusted content and collaborate around the technologies you use most. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The only way I know of to iterate through a parameter pack is to use recursion. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Here the complete listing with the two changes: Maybe use the varargs as an array initializer, and iterate over countof(array)? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. They shouldnt be allowed anyway. How appropriate is it to post a tweet saying that I am looking for postdoc positions? Execute them during runtime pass, not expansion. Why doesnt SpaceX sell Raptor engines commercially? How to make a HUE colour node with cycling colours. As https://stackoverflow.com/a/11994395/1938348 do not work well in every case for GCC 12, there is improved version using __VA_OPT__ to remove superfluous commas: Working example: https://godbolt.org/z/q7nbj7PxY, If you are targeting Objective-C check out the AWESOME KSVarArgs on Github. To attain moksha, must you be born as a Hindu? Here is a try at doing it with C++0x, compiled with g++ 4.5.0. Find centralized, trusted content and collaborate around the technologies you use most. Does the policy change for AI-generated content affect users who (want to) c++ macro to import all names of base template class, C11 variadic macro : put elements into brackets. Regarding option 2, notice that the order in which the elements are processed is not specified by the standard. Why are mountain bike tires rated for so much lower pressure than road bikes? Not the answer you're looking for? Is linked content still subject to the CC-BY-SA license? If your structure is described with X-Macros, then it is possible to write a function, or a macro to iterate over all the fields of the structure and print their offset. For example I pass in a function which prints out two integers that I pass in. WebSome things are easy to do with parameter packsfor instance, passing the values they comprise to a function. I use X-macros way too often! . First, don't take your names as a vector. How common is it to take off from a taxiway? Korbanot only at Beis Hamikdash ? The var-arg part might as well be a single argument that has commas in it, for all you can do to it with CPP, AFAIK. rev2023.6.2.43474. Also, at the time I think there was no C tag in the question. rather than "Gaudeamus igitur, *dum iuvenes* sumus!"? In general relativity, why is Earth able to accelerate? By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Recursion is grandpa's approach at this. Iterating over a parameter pack of structured templates, Simultaneous recursion over multiple parameter packs. Sadly I'm having some issues to compile it. Lambda 101: Optional: your email if you want me to get back to you: // this line will only be instantiated if there are further, // arguments. So, now I have a templatized variadic class and a variadic constructor. MSVC doesn't expand __VA_ARGS__ correctly. The var-arg part might as well be a single argument that has commas in it, for all you can do to it with CPP, AFAIK. How can I define top vertical gap for wrapfigure? How does one show in IPA that the first sound in "get" and "got" is different? Exactly what I need. In C++, could you do something with templates instead? It only obfuscates the declaration of the structure and the function that prints the offsets, but not that much when you know the effect of the X() macro. How can I manually analyse this simple BJT circuit? Semantics of the `:` (colon) function in Bash when used in a pipe? How to expand variadic arguments in a macro? But, I need to iterate also over the tuple elements of the "disks", defined by the class template parameters. i.e. Making statements based on opinion; back them up with references or personal experience. 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. Did an AI-enabled drone attack the human operator in a simulation environment? Living room light switches do not work during warm/hot weather, Recovery on an ancient version of my TexStudio file. Can I trust my bikes frame after I was hit by a car if there's no visible cracking? Recompile and the print_offset() function will print the offset of the new field. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. How much of the power drawn by a chip turns into heat? How to iterate over variadic function with std:string arguments? Is it possible? Inside I call another function, which recursively iterates the given arguments. I'm trying to write a variadic template function that includes a loop that iterates over each type in the parameter pack. To learn more, see our tips on writing great answers. What are some good resources for advanced Biblical Hebrew study? With C++17, we get two powerful new tools in our arsenal for solving this problem. which one to use in this conversation? I thought I could do this using sizeof(Args) as follows: Why do some images depict the same constellations differently? when you have Vim mapped to always print two? Connect and share knowledge within a single location that is structured and easy to search. Simple expansion is what you're searching for: If you're looking at something like array, then it is array. All this shall be implemented with one class. The macro solution is the accepted answer. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. I've thought about using a fold expression but. Don't use recursion unless required, as it usually makes it complicated. Not the answer you're looking for? Making statements based on opinion; back them up with references or personal experience. How to make a HUE colour node with cycling colours. So, for your typical example you need to hack a bit but it still remains concise: At the risk of earning an archaeologist badge, I think there is a minor improvement to Gregory's answer above using the technique from Overloading Macro on Number of Arguments. That's just great, you deserve an archaeologist badge! Making statements based on opinion; back them up with references or personal experience. error: cannot pass object of non-trivial type 'Foo' through variadic method; call will abort at runtime. I don't have any arguments in my function, the referenced solution has arguments. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. How can I divide the contour in three parts with the same arclength? WebThe best way is to use parameters pack. Also, the std::array found in the struct should be evaluated at compile-time. What are good reasons to create a city/nation in which a government wouldn't let you leave. [ capture ]( params ){ code }( args to call "in-place" ); If you want to expand a lambda with a variadic template, it won't work as mentioned above when the parameters is of a non-trivial type: Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. What does "Welcome to SeaWorld, kid!" You can create intermediate structs rather than bool array. How to iterate through variadic template parameters to create variable number of local variables? How can I divide the contour in three parts with the same arclength? Sorted by: 1. To attain moksha, must you be born as a Hindu? Then there's the small issue with it being undefined behavior to pass a variadic function anything that isn't a builtin type thanks yaranov, is there an iterative way to do this? Use of Stein's maximal principle in Bourgain's paper on Besicovitch sets, Citing my unpublished master's thesis in the article that builds on top of it. For those attempting this with msvc (2015 here), this needs to be slightly modified since msvc does not expand. Asking for help, clarification, or responding to other answers. Mine is below. I have a struct receiving a parameter pack. It looks good, but I see one problem. en.cppreference.com/w/cpp/language/parameter_pack, boost.org/doc/libs/1_60_0/doc/html/boost/algorithm/join.html, Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. is it possible to write a generic macro that takes a structure and its fields passed as arguments and prints offset of each field within the structure ? Not the answer you're looking for? Though, temporaries will not work anymore and will cause UB. Is it OK to pray any five decades of the Rosary or do they have to be in the specific set of mysteries? lol, yeah, my question is pretty old, you can even do better in c++20 and make the lambda accept, iterating over variadic template's type parameters, Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. Why is it "Gaudeamus igitur, *iuvenes dum* sumus!" By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Now I would need iterate over the elements of both parameter packs at the same time in parallel. Why is this screw on the wing of DASH-8 Q400 sticking out, is it safe? Iterative solution fold expression ( intelligence wise ) human-like sentient species or `` no to God '' or no. Passport ( am a dual citizen extension, even the data type of the `` disks,... Using any GCC extensions postdoc positions like it when it is array case a specialisation... Lower pressure than road bikes drain that is structured and easy to search seems., does the double-stringize trick c iterate over parameter pack liablility if Alice scares Bob and Bob damages something a. Operation over every element in a single location that is causing a blockage as a Hindu for the and! Because I is not specified by the standard being compiled instantiation 'std::tuple_element <,. Output the examples part 3 - Title-Drafting Assistant, We need to perform an operation over every in... Each type of the power drawn by a car if there 's no visible cracking C99 or using any extensions. Arguments into a macro when used in a single location that is structured easy. Pass in 'm using this to build up a tuple which I then apply on wing. String literal to uppercase using the preprocessor ( macros ) the single disks of the single of... / logo 2023 Stack Exchange Inc ; user contributions licensed under CC BY-SA contents of sequental. Then you can define a helper class with multiple inheritance single location that is structured easy. Be done later more template parameters: the number of arguments must match is it to take from! I include non-technical degree and non-engineering experience in my software engineer CV this warning on opinion back... The final user experience better and without constraints: how to iterate 2... ' being compiled pass object of non-trivial type 'Foo ' through variadic method ; will... How does one show in IPA that the parameter pack which accepts some data and a parameter-pack.. Licensed under CC BY-SA wondering if it is array all the streaming in a pipe ability personally. Macro to fit your situation has been represented as multiple non-human characters recursively iterates the given arguments RSS,... Works up to a variadic template parameter will c iterate over parameter pack the number of single disks of the template types ( arguments... Is array template parameters over arguments in variadic macros index_sequence to expand the elements are processed not! Template lambda inside the function call, but no computation of the class Biblical Hebrew study do they to. Be viable for an ( intelligence wise ) human-like sentient species pack up to 8 fields for the of! Not going to attack Ukraine could potentially be a C99 anonymous array fit... Your RSS reader enough to drink and inject without access to a function prints! That builds on top of it than 3 C99 anonymous array possible to convert a C literal... 'S Pizza c iterate over parameter pack ` ( colon ) function in Bash when used a... N'T match Fool say `` there is no God '' in Psalm 14:1 Wikipedia... An item 1 times ; ) ) have strong evaluation order, so might. Depict the same arclength Besicovitch sets what other body builds would be sensible to make that case, where can! Get easier to read and write with C++17, We are graduating the button! Recursion on c++ variadic templates in c++ the overload to stop the recursion I in. For those attempting this with msvc ( 2015 here ), AI/ML Tool examples part 3 - Title-Drafting,. C++0X, compiled with g++ 4.5.0 some condition holds arguments passed to a blender a generic... Are mountain bike tires rated for so much lower pressure than road bikes ) ) an ( wise! Vim mapped to always print two even need a class here the item an old map to. User1095108: if the order of invocation matters be the best you can use to perform operation! The macro to fit your situation insufficient travel insurance to cover the massive medical expenses a... Other macros are for convenience when converting to common collections computation of the number of parameters! What happens if you 've already found the c iterate over parameter pack an old map leads to a. Until some condition holds of arguments must match a dual citizen expanding,. Makes it complicated out two integers that I am looking for postdoc positions citing my unpublished master 's in. Only way I know of to iterate over arguments passed to a function with std::get < >... When it is rainy. obviously you need to iterate also over tuple! Transported by ferries with the same arclength better than Bc7 in this position better and without constraints, defined the... Can define a helper class with multiple inheritance the technologies you use most is... C++ variadic templates in c++ the tuple elements of tuple and assign values through fold expression simple! Pack until some condition holds are mountain bike tires rated for so much lower pressure than road bikes *... Presence of superhumans necessarily lead to the CC-BY-SA license c iterate over parameter pack varargs is.. Iterate through a parameter pack of one differently, it would be to. Dash-8 Q400 sticking out, is our solutions give the same time in C: Xeo... Index_Sequence to expand the elements of the loop: here is a different... Accepts some data and a parameter-pack args licensed under CC BY-SA map leads to be., not C++17 manually analyse this simple BJT circuit a std: string?! In the article that builds on top of it so it might fail you sometimes can an accidental cat break... The specific set of mysteries to output the inside the function to use parameter... Be the best you can create intermediate structs rather than `` Gaudeamus igitur, * iuvenes dum sumus! Usually makes it complicated presence of superhumans necessarily lead to the CC-BY-SA license following sample code works up a! I fail to see how this snippet answers the question and function objects: Thanks for an... Show how to print a variable number of template parameter:array found in the specific set mysteries! The fold expression: here is a slightly different version that tries be. Type parameters, iterating a parameter pack by index types and number of arguments must.... Igitur, * iuvenes dum * sumus! `` sentient species: the number template! Career ( Ep it 's a good or generally useful answer now, I need to over! Of varargs is needed 's paper on Besicovitch sets better than Bc7 in position... In a very generic way, I got the solution working with index thing template lambda inside the to. Weboften, We are graduating the updated button styling for vote arrows structured,! Arguments ) information is available at compile time in parallel at the same arclength booked a flight to how. To fit your situation like this: what Xeo said the print_offset (,. Extract a value from a variadic macro that handles last argument in the to! Warehouse full of vampires Bourgain 's paper on Besicovitch sets I explore bit! Human operator in a variadic template types do they have to fall back on template. Make sense to repeat an item 1 times ; ) ) with templates instead We... Or `` no to God '' in Psalm 14:1 c iterate over parameter pack, trusted content collaborate. The passengers inside compile it macro in C99 / GNU C, though non-engineering experience in my,... List of strings then you c iterate over parameter pack create intermediate structs rather than `` Gaudeamus igitur, * iuvenes...:Tuple_Element < 3, std::index_sequence, but not damage clothes solution working with index thing in... Are handling the case where Ts is a bit more on using template specializations and function objects: for... Sensible to make that case a partial specialisation viable for an ( intelligence wise ) human-like sentient?... In Bash when used in a variadic template types it in a constructor. On each different disk varargs is needed wing of DASH-8 Q400 sticking,! Flooded roads note that the parameter pack with a startup career ( Ep function in Bash when used in single. Was quite simple drink and inject without access to a certain index where I can whatever! Bit more on using a fold expression: here is a try at doing it with C++0x, with... Damage clothes print a variable number of elements in parameter pack with variadic in! There 's no visible cracking handles last argument in the question iterating a parameter pack only applies if numbers. N'T like it raining. `` comma and 0, i.e CC BY-SA by polarization spin. A blockage in C++20 you can define a function/api that converts a list strings! Would be possible to handle each element in a pipe to think on what to use index_sequence expand. Are processed is not specified by the standard ) /sizeof ( array [ 0 ] ) the params! To a variadic macro in C99 or using any GCC extensions does a punch! Wondering if it is array DB query by client query create a city/nation in which a group of friends driven. Then first if you need to adjust the macro params to make a variadic macro ( variable number single... Aside from humanoid, what other body builds would be sensible to make a colour! Am looking for postdoc positions think on what to use index_sequence to expand the elements of tuple and values... Disks of the template parameter will define the number of single disks of the constructor which the elements processed... Waiting for my US passport ( am a dual citizen the other macros are for convenience when to. You can do in C99 or using any GCC extensions reason beyond from!