C macro overloading. Preprocessor Definition in function parameter.

C macro overloading # Function overloading in general In very simple terms, function overloading is the facility provided by programming language A list of the traits, such as Add, that overload operators can be found in core::ops. Whenever a macro name is encountered by the compiler, it In C, function overloading is not a built-in feature, but it can be achieved through a technique called "name mangling" or "function name decoration" (more on that in an upcoming post). The restrictions on the C++ Macro overload Language: Ada Assembly Bash C# C++ (gcc) C++ (clang) C++ (vc++) C (gcc) C (clang) C (vc) Client Side Clojure Common Lisp D Elixir Erlang F# Fortran Go Haskell Java Javascript Kotlin Lua MySql Node. c" which I execute symbolically by overloading (almost) all operators. Support for overloading of macros was added in Erlang 5. The source, as you wrote it down, gets fed into a preprocessor. h This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. So foo needs to be some #define constant (catching both cases) that maps onto . Variadic function calling a variadic macro. ) In C, a macro is a piece of code in a program that is replaced by the value of the macro. Function-like macros can be used to create custom functions that perform specific operations on the given arguments, providing code abstraction and reusability. 1. Commented Jun 16, 2013 at 20:11. Overriding macros using compiler options. Generic selection is similar to overloading in C++ (where one of several functions is chosen at compile time based on the In that case macro could only contain only 1st argument as fixed one. C++ Type Modifiers There's no guarantee that the new operator calls malloc() under the hood. Generic selections, introduced in C11, gave the programmers the ability to write similar type-dependent code. Any text that is not one of those should be rejected. One can say that PP_NARG() should return 1 for the same reason PP_NARG(,) should return 2. Pure standard C99 macro implementation to overload and set optional default parameters of C/C++ functions. 57. But if you are going to do something GCC specific anyway, then why not use the old-fashioned GCC extension: Function overloading is a feature of object-oriented programming where two or more functions can have the same name but different parameters. Modern C, AKA C11, can do more than you think. This sometimes forces C developers to use ungainly function names like print_int() and [] Master C programming with our C Programming Course Online, which covers everything from the basics to advanced concepts like data structures. OPEN Say I have a function of the following definition: void magicFunc(std::string x, int y) { std::cout << x << std::endl; } And I now wish to supply a default value for the string parameter, x, without breaking the API. The C standard mandates that the only place the identifier __VA_ARGS__ can appear is in the replacement list of a variadic macro. The trick has limitations: it works only for 1 default value, and the argument must be the last of you function parameters. Is there a way to force C preprocessor to evaluate macro arguments before the macro. So there's no way to evaluate their type using a __typeof__ of Though normally we simply invoke something like gcc file. In the standard 6. This allows you to override a single function from any Macro overloading. Wondering if there is a to overload a function in C. Better oop practice: arguments of the class functions. The program would start by calling the unique main() of the appropriate form. You're just obscuring a count argument that's needed by the called function to know when it has to handle the extra arguments versus knowing this implicitly from the other given arguments. you can make 3 overloaded normal or It is possible to use the standard C /C++ variadic args in macros, at least in gcc (EDIT: apparently they are standardized, and MS c compiler also has them). Or leave out the macros altogether. Variadic macros with zero or more additional arguments. For example, one might provide several overloaded versions of a tgsin function that invokes the appropriate standard function computing the sine of a value with float , double , or long double precision: As far as I know, no: CMake does not have macro or function overloading features like you have shown in your imaginary example. For a scalar macro, CREATE MACRO is followed by the name of the macro, and optionally parameters within a set of parentheses. the _Ctype array returns the type of a character. . (Not using any kind of block construct at all would just generate completely broken code, natch) How overload a define macro? Getting started with C or C++ | C Tutorial | C++ Tutorial | C and C++ FAQ | Get a compiler | Fixes for common problems; Thread: How overload a define macro? Thread Tools. The _Generic keyword was first introduced in C11 Standard. Overloading functions with the C preprocessor #c #preprocessor #programming. feel free to call me a dummy if you think this is a nooby question. to only enable code for certain platforms or compilers) . Introduction. The reason it decays to a pointer in the case that Chris gave is because he proposed a scenario that passed by value, which isn't possible for raw C-style arrays and therefore would enforce decay to a pointer. Preprocessor directives begin with a hash symbol and include #include, #define, In performing overload resolution, C++ prefers a non-template function over a template instantiation, as long as I'm trying to do some sort of object oriented programming in C. You could write new macros, change the existing ones. Improve this answer. Below is Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Here, the problem is CTR_REGISTER_TYPE() macro, which appends a type to a MPL-like vector related to a specific tag. The C preprocessor doesn't do operator overloading, no matter how clever you are. As for whether you can or not, give As part of the template auto paper, we also got a new deduction rule in [temp. In your case since you don't want SOME_MACRO anymore once the SOME_MACRO() is defined, you may do following in the intended (header) file: #undef SOME_MACRO // hopefully it is not a standard macro! #define SOME_MACRO() // use __VA_ARGS__ Now in the code you can call Function overloading via macros depending on variadic arguments . Show Printable Version; Is there some way to keep to use overloading with variable number of arguments? Specific example is as follows: // Third party class class ABC { public: void addValue(int); void addValue( The actual interface is three arrays, e. Ignoring or redefining GCC Standard Predefined Macros. To use, include the following: extern crate overload; use overload::overload; use std::ops; // <- don't forget this or you'll get nasty errors where "tag" is a string literal with the anchor name of the item where the Enforcement rule appears (e. The included pp_iter. Macro definition in C and C++. #include&lt;iostream&gt; #define CONCATE_(X,Y) X##Y #define CONCATE(X,Y) CONCATE_(X,Y) #de This looks the same to a developer as if count_overload were a variable argument function. Some C macros (and an associated code generator) to count and iterate over variadic macro arguments. The reference you found is correct: C does not support overloading, as such. The macro is set to 201703L if the /std:c++17 compiler option is specified. It's macro overloading. 0. overloading new and delete. #define foo ) #define foo(arg) ,arg) That is, I want foo (note: not a macro function) to map to one thing, and I want the macro function foo(arg) to map to something else. If those getters are inlined in code (and the implementation actually inlines those getters, which it is also not actually required to do - since Clang provides support for C++ function overloading in C. Failure to Pass Arguments to a UDF in VBA for Excel 2007. It's important to place all text to be generated within an interior loop inside of a callable macro so that parentheses and commas don't screw up the macro API, since these delimit macros on their own. 10. Function-like. 32. preprocess it looks like Only code compiled as C++ sets it. – supercat. This is generally a good way to make your code completely unreadable. without the i, the control statement is roughly equivalent to: C macro overloads are provided for up to eight arguments. See overloading below. If you want overloading, you need proper functions (not preprocessor tricks) - those functions can be standalone I'm adding a macro used in C file which should take a variable number of arguments, which should be handled based on the type and the number of arguments differently. 45. Behaviour beyond this is C has no way to avoid this problem in the general case, but a convention that many people use is to always put an underscore at the end of the name of each local variable defined inside a macro, and never put underscores at the ends of any other identifiers. See this for more info. You can't overload on the absence of a parameter. Are there any semantic reasons why C could not support overloading of static and static inline functions, given that compilers are not expected to give a static function any particular link-time name (and in many cases have to mangle names to avoid link-time errors if static There are already many questions/answers about macro overloading. An object-like macro is a simple identifier that will be replaced by a code fragment. Preprocessor macro without replacement C++. Gain a deep understanding of C and enhance your problem-solving abilities with practical coding challenges. It has type generic macros that can accomplish something similar to function overloading in C++ with the new _Generic expressions. – I'm trying to achieve method overloading in C, preferably using macros so the header/library can handle the definitions and declarations instead of putting that onto the user. The closest you can come in C is the #undef directive, which simply undefines the macro, allowing it to be replaced:. 5 Macros. It is inspired by the article "C/C++ Preprocessor Metaprogramming" by Saad Ahmad and various C preprocessor tricks, tips, and idioms. - jason-deng/C99FunctionOverload //Bad; can't redefine macros; uses later definition. Commented Feb 11, 2013 at 20:06. Subtle but important difference. This article explores a technique to overcome this limitation. If function1() is actually a macro, just using { } requires you to omit the semicolon at the point of use, but do { } while(0) lets you use exactly the same syntax as for a real function. The following code has a FLAG controlled macro to use func1 or func2 when compiling. 2014-09-15 ⋅ Comments. It is popularly used to replace a symbolic name with a numerical/variable represented as a 2 7 Overloaded Operator Functions Rational operator + (const Rational &left, const Rational &right) { // return sum of two rational numbers Rational result The type-generic math macros from <tgmath. An overloaded macro has more than one definition, each with a different number of arguments. you can make one macro that takes an additional parameter to choose what code to run. Add a C Preprocessor, Macro "Overloading" 17. One of the first thing that happens to a source file is preprocessing. 19. h A set of macros building on those defined in pp_iter. Overloading Macro on Number of Arguments. There are two kinds of macros. Macro overloading. Back to top 13. While starting from 2nd all are variadic. type]:. In the latter case, the transformation macro I have a bunch of printf debug helper macros and it would be pretty cool to have to not specify the type, is there anything you can do to allow something like macro overloading in c(can be gcc specific if its available in gcc 4. Understanding DEFER and OBSTRUCT macros. But, I cannot find a way to apply it to my particular problem. The base macro ksva_iterate_list() iterates over the variable arguments, invoking a block for each argument, until it encounters a terminating nil. c preprocessor passing multiple arguments as one. f_1 + f_2 for example can't be simple std::array<double, M> (*)(Point)s. Can macros be overloaded by number of arguments? 2. 2. 3 min read. Here's the new myfunc. C preprocessor macro expansion. C\C++ Preprocessor different arg for overloaded macros. Overloading macros with variadic arguments. It is recommended to always use the inline function instead of the macro. Macro overloading support in C. (weak))foo(x)' to define your macros. "It is really silly to compile your C code with a C++ compiler" => Not considered so by everyone (including me). 436. I looked into several macro tricks but couldn't figure out a way to do this. Related. deduct. Macro expansion with overloading. Should 6. rodata section). Variadic Macros and Overloading (requires C99) One of my favorite uses of the preprocessor for C is overloading. The macros, e. C++ concatenating macro definitions. Macro overloading is not possible. If it's pure C++, it's easily achieved by overloading the function, but how would I pass the variadic arguments from C macro into C++ with this mixture of C and C++? Macrometa (MCMT) is a powerful macro-based library for C that enables metaprogramming, allowing developers to generate complex code during compile-time using preprocessor macros. h includes macros to handle up to 63 arguments. What it does have (assuming we're talking about the actual C and not historic versions) is a generic selector which allows you to write your own macro which does dynamic dispatch. EDIT: added includes and the struct definition, so the code now is compilable. // Here, we make `Add<Bar>` - the trait for addition with a RHS of type `Bar`. Etc. But you can make a template <class Return_type, class Args> struct Math_function; wrapper holding a callable which can then be overloaded and you can get Math_function{f_1} + f_2; to compile. Macro is defined by #define directive. 3: Classes and Objects - Constructor and Destructor. Overloading new, delete in C++. Preprocessor macro definition of a macro definition. Define a macro with defined(X) 2. ; A template function can be overloaded either by a non-template function or using an ordinary function template. I have the following 3 macros: #define First Objct t; t #define Second a() / b() #define Third ; Showing Compile error: ambiguous name detected, while overloading functions. ### 3. Stringizing Operator (#) The stringizing operator (#) is a preprocessor It is provably impossible to change a macro in any way without rewriting it from scratch. C Preprocessor, Macro "Overloading" 4. 4, or bounds. The macros on this site only work for a #define with one argument, mine has two. Function overloading in C is introduced using the overloadable attribute. You can't declare its prototype in an outside file (leaving the linker to link it in) without putting its full definition in said outside file. C++ preprocess macro with 2 arguments. 9. Syntax of _Generic in C_Generic( (express. It is possible that MSVC++ have some kind of extension, but that still doesn't make it less "wrong" IMO. Context. Compile and link the file with your reimplementation (override. From this #define reference: "If the identifier is already defined as any type of macro, the program is ill-formed unless the definitions are identical. 2 Macro Overloading C does not support function overloading, but you can achieve a Overload C macros. Raw. C++ Overloading Macros. Every serious programmer knows it. Using nested macro with different number of arguments in C++. The following macro-based approach allows for optional and The C preprocessor can't be used to overload operators, since it doesn't know the types of a and b in the expression "a+b", see this question. (to set an initial size of the stack) The trick in these macros is that PP_HASCOMMA() expands to 0 when called with zero or one argument and to 1 when called with at least two arguments. ATTR processes XXX into a macro ATTR_IMPL_XXX(), and XXX can have a variable number of arguments (these variadic args are just passed to another macro, Overloading Macro on Number of Arguments. Redefining Macros for logging. 8. #define POSTFIX _ABC //_ABC should be mentioned only there #define PROTOTYPENAME(symbol) symbol ## POSTFIX #define PROTOTYPENAMED(sym) PROTOTYPENAME(sym) int PROTOTYPENAMED(Function)(int In C, a macro is a piece of code in a program that is replaced by the value of the macro. Overload C/C++ preprocessor macro on structure of its argument. This will do the former in release builds (compiled with NDEBUG), and But the OP title is misleading, this isn't function overloading at all. Whenever the name is used, it is replaced by the contents of the macro. It is called object-like because it looks like an object in code that uses it. As Cat Plus Plus indicates in her answer C11 has the additional construct _Generic to program type generic macros. Defining a Preprocessor Macro. Note that if overloaded macros are actually required, BOOST_PP_OVERLOAD cuts out the boilerplate. And for macros, this is a perfectly reasonable requirement if there exists a macro solution that works in both languages, and most macro solutions indeed do work in both languages. It can be implemented with C macros to imitate function overloading. Of course I can't actually overload the macro. Hot Network Questions Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Visit the blog By macro I'm assuming you mean something like #define getline(a) //code here The first thing that came to mind when I read this was why would you want to? Since you can overload functions and inlining functions achieves the same effect as macros there's no need to even write macros, much less overload them. If you wanted to overload an operator using the preprocessor, then it would have to learn every type (including custom types) used in your code, and it would have to perform static type checking in order to determine which function to Template: A template is a tool that reduces the efforts in writing the same code as templates can be used at those places. <operand_type> Both of those functions are useful in combination with the __LINE__ and __COUNTER__ macros. 255. Commented Mar 8, 2015 at 0:33. c to compile our source file, and though we say we 'compile', there's a pretty bunch of various things happening under the hood. The parmN argument to va_start was intended to be an aid to implementors writing the definition of a conforming va_start macro entirely in C, even using pre-C89 compilers (for example, by taking the address of the parameter). 256. 6. Take the Three 90 Challenge!Complete 90% of the course in 90 days, and earn a 90% refund. It would remove many more usages for macros (especially X-Macro), but it requires a more complex build system, especially because we either need to have a prebuilt code-generator or compile it with GCC has a handy ## extension on variadic macro that allows you to simulate a default argument. The overloading function must have no output argument and a single input argument. Function overloading is a feature of object-oriented programming where two or more functions can have the same name but You cannot overload operators without a user defined data type being involved. the is macros are for convenience to use the _Ctype array. Therefore, the expansion is ends up being: _myfunc_1(1) The second call ( I know that macro overloading isn't a thing in C, but I'm wondering if there's another way to achieve this behavior from FOO. In addition, the preprocessor adds backslashes to escape the quotes surrounding embedded string literals, if Obviously, C language provides overloaded operators within the core language, since most operators in C have overloaded functionality: you can use binary + with int, Nonetheless, GCC can be made, using macros, to support a form of overloading which is not supported directly in languages with operator overloading. h: you cannot directly overload macros. The CREATE MACRO statement can create a scalar or table macro (function) in the catalog. Leaving both C and C++ is perfectly acceptable if the goal is to have a solution that works in both languages. Track your It works unless the variadic function/macro is passed the string literal defined by VOID as a sole argument. Have you ever wanted to write a “for each” loop over all the args of a variadic macro? Or have you ever wanted to overload a macro on the number of arguments? (If you’re saying to yourself, “good grief, why?” — I’ll describe a use case at the bottom of this post. Multiple macro names wouldnt work well because of a combinatorial explosion: with two variable names I would need separate macros for foo(a,b), foo(a,_), foo(_,b) and foo(_,_). Share It's possible to write a macro that evaluates to the number of arguments it's called with. However, I agree that it would be great to show how to achieve something similar with traits [1] and macros. #define GET_MACRO (_1, _2, _3, NAME, ) NAME #define // Define a function-like macro with variadic args () wrapping one of the OVL_m_n() macros // where m is the minimum allowed number of arguments and // where n is the maximum allowed In C, function overloading is not a built-in feature, but it can be achieved through a technique called "name mangling" or "function name decoration" (more on that in an upcoming post). I'm trying to overload a macro by the number of parameter. OVERLOADED_MACRO(ii, __VA_ARGS__) #define ff3(c, a, b) for (int c = int(a); c < int(b); ++c) #define ff2(c, b) ff3(c, 0, b) #define ii2(a, b) ff3(i, a, b) #define ii1(n) ii2(0, n) int main() { ff (counter, 3, 5) cout << "counter = " << counter << endl; ff (abc, 4) cout << "abc = " << abc Single header providing one macro allowing overloading of other macros based on number of passed arguments. So in the macro itself, you could extract 2nd argument to macro separately and pass it as 2nd argument of the SendMsg. To prevent the confounding of the C Otherwise, the behavior is undefined. The keyword AS is next, Hasn't u/awegge already answered your question? Anyway here's a relevant quote from the rationale (PDF page 150): . 14. 5/OTP R13B04. N has an upper limit of 3, Macros (The C Preprocessor) Next: Conditionals, Previous: Header Files . Such macros are called non-syntactic because they allow code that doesn't look like syntactically correct C. "message" is a string literal Depends on how you define "better" - without that (by definition) no canonical answer is possible. I have to be able to detect (condition) ? this : that and extract condition, this and that for usage in my symbolic Hello all! coming from higher level languages to learn C. Syntax of _Generic in C In C, a macro is a piece of code in a program that is replaced by the value of the macro. , for C. Therefore, C++ has certain macros to represent these numbers, so that these can. Overload C macros. 3. Can macros be overloaded by number of arguments? 23. Creating macro for operator << 2. Overloading Pre-processor macros for {zero, one} arguments. Bulky macro definition overload. In C, # and ## operators are preprocessor operators using in macros for token manipulation. To review, open the file in an editor that reveals hidden Unicode characters. The [] characters in your input are not inside parentheses, therefore they aren't part of a macro argument, and they aren't alphanumeric characters so they aren't part of a macro name. ) This page titled 14: Overloading in C++ is shared under a CC BY-SA license and was authored, remixed, and/or curated by Patrick McClanahan. 2. Redefine Macro in existing C library. I thought It can be implemented with C macros to imitate function overloading. C preprocessor macro specialisation based on an argument. However, metaprogramming in C is utterly castrated: we cannot even operate with control flow, integers, unbounded sequences, and @ThomasMatthews, I wouldn't change the tags. 47. C macros provide a convenient method for code reuse and parameterization. This is typically done by "mangling" the name of a function, and thus including the types of its arguments in the symbol definition. the empty token). To distinguish between these two cases, I used PP_COMMA __VA_ARGS__ () , which returns a comma when __VA_ARGS__ is empty and returns nothing when __VA_ARGS__ is non-empty. 26. I have some macros of the form ATTR(XXX()). Research project here. Overloading C Preprocessor Macros - Discimination Based on Call Syntax. "That means your program is ill-formed according to the standard. [] # and ## operatorIn function-like macros, a # operator before an identifier in the replacement-list runs the identifier through parameter replacement and encloses the result in quotes, effectively creating a string literal. 134 it is “Rh-public”), the name of a profile group-of-rules (“type”, “bounds”, or “lifetime”), or a specific rule in a profile (type. 73. It may not be used as a macro name, macro argument name, or within a different type of Some people, myself included, prefer the style where the # is always in the first column to make preprocessor lines stand out since an indented # is harder to notice. 2). Types Of Macros in C. – I am working with c++ Macros, trying to implement on certain pattern. Detecting 0 may indeed be handy in some cases, but the solutions seem to either be less general (requiring that first token to be pasteable; which may or may not be okay depending on what you're using it Overload C macros. Macros There are two kinds of macros: Object-like. redefining a macro not working as expected. (I couldn't find a link to the place where I first saw it. Macro definitions need not be terminated by a semi-colon(;). – Qaz. Hot Network Questions How do you build Mizar locally? Does launch on warning assume incoming ICBMs carry nuclear warheads? Help me identify this chip (8 pins) New 90 TB/10 drive RAID 5 In this example, the proper solution is using a macro. Overloading on a number of arguments: Macros facilitate code re-use, macros are the building material that lets you shape the language to suit the problem being solved, leading to more clean and concise code. Whenever a macro name is encountered by the compiler, it replaces the name with the definition of the macro. Define a preprocessor macro through CMake. Replace C macro for a function call with a C++ template? 0. C/C++ logging facility that supports conditional function calls depending on log-level. cmacro_overload. h>, introduced in C99, were implemented in compiler-specific manner. Other functions in C, such as printf, determine how many and type of arguments to @dreamlax, we're moving from the general (C) to specific (gcc/linux) solutions now - it would be a good idea to clarify what you're running on so as to better target the answers. Your choice of display_float as the default in the _Generic is surprising, but changing it to display_void won't help much; you'd have to provide an argument to the display macro, and that would be passed to whatever function is in the default clause, and if that was display_void, it would be expecting no arguments. macro in function declaration. operator delete must undo whatever operator new did. . Over reliance on macros. See this page for some information This family of macros is intended to allow the transformation of a __VA_ARGS__ list into a single C expression OR one C expression per argument. If we use boost. But nowadays the situations where you want to use macros are really rare (e. One of the most widely used macro systems is the C preprocessor (CPP), which is included in both C and C++ as the first step in processing a program. By convention, macro names are in generally written in all UPPER CASE to draw attention to the fact than a name is a macro and I understand the good solid reasons why exportable functions cannot support overloading. Even if there was, your approach will only affect your own code that calls malloc(). use std::ops; struct Foo; struct Bar; #[derive(Debug)] struct FooBar; #[derive(Debug)] struct BarFoo; // The `std::ops::Add` trait is used to specify the functionality of `+`. What is good practice is to get away from using macros for defining constants and doing some crazy C level coding stuff to create container templates. Override macro from the command line. The above sizeof_overload() macro works similarly. 5. The only useful macros here would be for an array initializer or member access (subscript, dereference, ), other than that no other macro or inline function or _Generic voodoo needed (remember, it's being said that macros are evil). Inspired from this kind of solution, I have written below code, which simulates "overloading of macros". If there is exactly one input parameter i. Variadic macro expanding. More sophisticated version: The display of new objects defined by tlist structure may be overloaded (the default display is similar to list's one). Overloading a macro with two arguments. I can't see why, but when I pass 3 parameters, contructor1 gets called. Hot Network Questions in place of your former for loop headers. Now I am trying to create a macro, like this: Overloading Macro on Number of Arguments,but that would work with my case. Microsoft’s old traditional preprocessor is unhappy with OVERLOAD , "PP_NARG() fails to return 0" isn't necessarily a problem. In this case, only a call of somefunction("__variadic_VOID__"); will cause unexpected behavior; passing a variable with the same value as the string literal does not cause unexpected behavior. Preprocessor macro calling inline function. #define FOO X #undef FOO #define FOO Y #undef FOO #define FOO X The problem is that you cannot know the 'old' value of FOO once you redefine it - so your values must be hard-coded in one place. , comma swallowing by the specific expression `, ##__VA_ARGS__` for GCC/CLANG, and implicit swallowing by However, what if you need to overload by types instead? In C11, that's easily possible using the _Generic feature. c). While C doesn't support function overloading natively, we can simulate it using macros. All macros assume that the varargs list contains only objective-c objects or object-like structures (assignable to type id). I have a macro of some value I wish to supply, and need a Optional and Overloaded Parameters with C Macros. Follow edited Oct 31, 2013 at 2:34. C - Variadic macro which expands into set of macro calls on each argument. g. A common theme in these answers is that we need a GCC specific hack. I'm working on a macro library and need Overall, overloading the macro on number of arguments and using an external tool (shell script or m4 preprocessor) to generate C source code is waay easier, easier to read, maintain and fix and also you can expand the macros on the tools side removing the burden of Macro overloading. In general, if you are new to Overload C macros. MSVC Preprocessor Bug - Overloading C/C++ Macro on Argument Count. creating new operator in c++ with/without preprocessors. There's a compromise between the two, which is to use the assert macro. – Provides a macro to simplify operator overloading. Can macros be overloaded by number of arguments? 5. The other macros are for convenience when converting to common collections. Lars Viklund Lars Viklund. They are known as stringizing and token pasting operators and are used in macro definition with #define preprocessor. In C macros may partially replace function overloading of other languages. Macro Redefinition. In short, that your technically illegal program (like, maybe overload the DEBUG_LOG macro and parse NULL for the second parameter to Log(), or something along those lines) Thanks for reading :) Mar 3, 2018 at 2:57pm UTC If someone could link me or even better program a simple overload for just one of the operators as an example would be incredible! c++; vector; operator-overloading; overloading; Share. MSVC doesn't expand __VA_ARGS__ correctly. h> in C99 and generic selection expressions in C11 as outlined on this site. They differ mostly in what they look like when they are used. A macro may only be a single SELECT statement (similar to a VIEW), but it has the benefit of accepting parameters. See for instance C++ core guidelines: CPL. h to facilitate auto-generation of string representations of members of an enum type. Change. This blog post (not mine) shows an easily expansible way of accomplishing the same goal (checking if a single argument is an actual argument vs. However, overloading is not natively supported in C due to its origins as a procedural language. Preprocessor Definition in function parameter. The macro is set to 202002L if C Preprocessor, Macro "Overloading" 45. Object-Like Macros. (Follow-up of Overload ternary ?: operator, or change to if{}else{} in included files. Overload macro as variable and function. No. If you want to redirect calls to allocate memory at a low level, you need to find out what function in your operating system's kernel is used to allocate memory and redirect it through some type of API hook -- all Notice: In those notes, I’m not considering external code generators or tools that can alter a compiled binary (for example for adding something in the . Share. e. 23k 4 4 At the time when compilers weren't that good at optimizing as nowadays, macros like this had their use. Controlling the executions of CPP Preprocessor. Modified 1 year, 7 months ago. c++ overload operator new delete, 2. I would like to conveniently assign values to my 3D images in C. Detect when multiple enum items map to same value. Hot Network Questions Function overloading is a ubiquitous technique in modern object-oriented languages like C++ and Java that allows defining multiple functions with the same name but different parameters. It is well known that C++ allows one to overload functions, and C does not. They are also very useful to write "function like" expressions that are "polymorphic" or "overloaded"; e. It is possible to overload macros, except for predefined macros. In this post, we will explore Uses only **standard C99** macros to achieve function overloading, no GCC/CLANG/MSVC extension involved (i. A macro is a fragment of code that has been given a name. The trick is done by combination of inheritance (ctr::Rank<>) and overloading (ctr::GetTypes()), so it is certain that overloaded version needs to be declared every time a type is registered at caller side. There are two types of macros in C language: 1. 3, you have: An identifier currently defined as an object-like macro shall not be redefined by another #define preprocessing directive unless the second definition is an object-like macro definition and the two replacement lists are identical. I think we have two options: As for errors, you will have to go to the exception route if you don't want to provide any extra parameters to your overloaded operator (another reason to use operator(). 13. As internal interfaces for your library you still would need the function declarations: String new_String_from_cstr(const char *str); String new_String_copy(String s); I can generate name for a function using an macro which is taken from C pre-processor defining for generated function names. In my C++ library, I am including C files using #include "aprogram. pp_enum. ). However, by default, macros cannot handle optional or overloaded parameters. Well, one could imagine how such a system would work. Sometimes, however, it makes sense to use non-syntactic macros when you want something that writes to a variable without having to pass it C++ move/copy constructor and assignment demo. StreamParam For this purpose we make use of declarative macros to implement a basic overloaded add function. The _MYFUNC_SEL macro returns the third argument, _myfunc_1. You could also simply use an inline function that takes the largest-possible integer or floating point type and let the compiler optimize it down when the argument is known to be smaller. When a function name is overloaded with different jobs it is called Function Overloading. Clearly this doesn't happen, but it's not too hard to imagine that it could, if it were desirable. However, what about giving it the type, something like this: out = (a*b+b*n) x c : {a,b,c->vector3, n->float}; Which would be preprocessed into: vector3 out = cross(add(dot(a,b), mult(b,n)),c); Because i want to write like : Complex c = new Complex(); delete c; – user2036677. timrau. You cannot create a macro to save the values for you Variadic macros tricks. 4. Preprocessor macro that inserts another preprocessor macro. something. Solution. But yes, the overload taking the array as-is by reference is a better conversion than letting it decay to a pointer. while 3rd argument to fucntion will be "%s %d" and then all the remaining variadics + "xyz" + 123. This rule allows the These include the OVERLOAD macro, which implements a well-known trick to “overload” any macro based on the number of passed arguments. Is it possible to define a macro from a macro. Escaping a # symbol in a #define macro? 4. I'm hard-pressed to think of what "C-only-isms" one really needs to make it worth not programming in the Overloading Functions in C. May be used for providing default argument values for functions. 3). The macro is the integer literal value 201402L by default, or when the /std:c++14 compiler option is specified. It assumes it is passed a floating point type, and CPP retains the comma when conforming to a specific C standard. So it would pick the one of the form int main(int argc, char *argv[]). In this post, we will explore There are various answers regarding the "overloading" of macros if the argument count is known; however their methods of determining the length of __VA_ARGS__ all work only to a finite, chosen number. VBA excel Overload another add-in function. This is what I currently have: C Programming; Overloading a variadic macro; Getting started with C or C++ | C Tutorial | C++ Tutorial | C and C++ FAQ | Get a compiler | Fixes for common problems; Thread: Overloading a variadic macro. VBA UDF multi-cell reference. Be careful, only the types registered by the typename function can be used in an overloading macros. Show Printable Version; It's possible to use C macros with gcc-originated extensions for such purposes, but it's somewhat icky. a The BOOST_OUTCOME_TRY macro uses C macro overloading to select between two implementations based on the number of input parameters. precompile options for function overloading in C. Is there any trick that might make a similar approach work for my "one argument / more than 1 arguments" case? Conditional Compilation and Debugging/Logging is the domain where macros are really handy and legitimate. Default arguments in C. Printf %px test. Macros Overloading. E. C++ Macros and overloading. You can use macros to overload a function or macro by the number of parameters, starting with one. I want to make it switch between the 2 function when compiling by using the "FLAG" macro (defining/ C preprocessor: redefine macro, macro overload. With C99 you already have possibilities to program macros that are in some sense type generic. Now I've read this answer about using _Generic however the problem is my functions have struct types. 2014-11-25. GCC includes an intrinsic C++ Overloading macro on undefined number of arguments. js Ocaml Octave Objective-C Oracle Pascal Perl Php PostgreSQL Prolog Python Python 3 R Rust Ruby Scala Scheme Sql Server Swift Tcl The only C functionality that's remotely close to overloading is limited type-generic macros of <tgmath. 4 min read. One of the things I'm stuck at is how to get an overload of a function based on the number of arguments passed. The preprocessor replaces all macro calls directly within the macro code. There is no requirement that an operator<<() be a friend, as long as the class provides accessible getters to the members. – Maybe there should be a new chapter about function overloading? Note that Rust does not have function overloading, hence having a "function overloading" chapter (with that exact name) may be misleading. Object-like macros resemble data objects when used, function-like macros resemble function calls. 7. In this article, we will learn about these operators and how to use them in C programs. Improve this question. Follow answered Sep 4, 2012 at 15:40. @mbratch: In this particular case, I'm using a macro to define a set of variables but some variables are optional and I want to avoid defining them. For example, you can't pass the OP's "add" around as a function pointer. Neither of default values or function overloading exists in ANSI C, so you'll have to solve it in a different way. I would say the arrays are fixed, the macros could be adapted to your use case. I've tried using variadic macros to choose the right macro (using the fact that if __VA_ARGS__ doesn't exist it's supposed to delete the last coma before it - GCC Reference ): It's not possible to overload macros (in the sense of having two variants of a macro that take different sets of arguments). 2: If you must use C, use the common subset of C and C++, and compile the C code as C++. 23. When the value of the argument corresponding to a non-type template parameter P that is declared with a dependent type is deduced from an expression, the template parameters in the type of P are deduced from the type of the value. ; Function Overloading: In function overloading, the function may have the same definition, but with different arguments. Edit: The C proprocessor is conceptually very simple, and it knows very, very little about C's syntax, and nothing at all about C's types. 1: Prefer C++ to C, CPL. 3 Macros ¶ A macro is a fragment of code which has been given a name. Anything that's not a macro name or a macro argument is going to be passed through by the Readers familiar with the C language know that the C language uses macro. Thread Tools. 2,146 1 1 gold badge 18 18 silver badges 15 15 bronze badges. Otherwise the comma is dropped as an extension to the standard. Ask Question Asked 1 year, 7 months ago. How to obtain the source location in an overload of operator new. Defining a macro or function multiple times will just lead to the last definition being used regardless of what directory scope that last definition was made at, since function and macro definitions themselves are not scoped. void stack_init(Stack* stack); but i also want to overload the function in case the user wants to include a size. Macro Overloading. One way is to use the token-paste ##__VAR_ARGS__, but pasted arguments are not macro expanded, which means that macros cannot be nested. ceeqji icucbj boghjcf reyvp tiw fvln uhcxjf tbse vsn mep