How Can I Handle Commas in Macro Arguments in C/C ?

Commas within Macros in C/C

One may encounter difficulties when utilizing macros that accept multiple arguments, especially when the arguments contain commas. Consider the following example:

#define FOO(type, name) type name

While it is straightforward to use the macro with arguments like:

FOO(int, int_var);

Issues arise when dealing with complex arguments involving commas, such as:

FOO(std::map<int, int>, map_var); // Error: 3 arguments passed to macro 'FOO', which takes only 2

To address this, one could introduce a custom type definition:

typedef std::map<int, int> map_int_int_t;
FOO(map_int_int_t, map_var); // Compiles successfully

However, this approach lacks ergonomics and requires additional type conversions.

An alternative solution involves defining a macro named COMMA:

#define COMMA ,

With this definition, complex arguments can be passed to the macro using the COMMA macro, for example:

FOO(std::map<int COMMA int>, map_var);

This method also allows for argument stringification, as illustrated in the following code:

#include <cstdio>
#include <map>
#include <typeinfo>

#define STRV(...) #__VA_ARGS__
#define COMMA ,
#define FOO(type, bar) bar(STRV(type) \
    " has typeid name \"%s\"", typeid(type).name())

int main()
{
    FOO(std::map<int COMMA int>, std::printf);
}

This code will output: "std::map has typeid name "St3mapIiiSt4lessIiESaISt4pairIKiiEEE"."

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