CODEWITHSUNDEEP
cgcctypeof
user2868331
user2868331

Reputation: 333

Converting typeof to string

Is there a way to convert gcc's typeof extension to a string, for example:

#define printType(a) printf("%s", #typeof(a))

So that I can do:

int a = 4;
printf("Type of a is: ");
printType(a);

And get the output of:

Type of a is: int

A possible use of this would be as follows:

#include <stdio.h>

#define indirect_print(a) print_##typeof(a)(a)

void print_int(int *i) {
    printf("%d", *i);
}

void print_char(char *c) {
    printf("%c", *c);
}

int main(void) {
    char C = 'C';
    int I = 100;

    {
        char *a = &C;
        indirect_print(a);
    }

    {
        int *a = &I;
        indirect_print(a);
    }

    return 0;
}

If possible, it should work for all types including structures and unions, without relying on adding every type to a list manually.

Upvotes: 17

Views: 3717

Answers (2)

too honest for this site
too honest for this site

Reputation: 12263

The preprocessor runs before the compiler. So all its replacements are performed before the actual compilation is started. typeof() is evaluated by the compiler, which would only see a string "typeof()" which will obviously not be evaluated.

So, the answer is: not for pre-C11. For C11, see the answer of @tmlen, but be aware there are some ambiguities about the _Generic type selectors which are resolved differently in different compilers, wich can result in problems with qualified types. There is a defect report about this issue, read Jens Gustedt's blob for details: https://gustedt.wordpress.com/2015/05/11/the-controlling-expression-of-_generic/#more-2256 (he also filed a defect report http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_423.htm).

Upvotes: 6

tmlen
tmlen

Reputation: 9090

Since C11, you can use a generic, see http://en.cppreference.com/w/c/language/generic. For example:

#define printType(a) printf("%s", _Generic( (a) , \
                                  int : "int", \
                                  long : "long", \
                                  float : "float", \
                                  default : "other type"))(a)

Every type that can be used needs to be listed.

In C++, there is also the typeid keyword:

#include <typeinfo>
#define printType(a) std::cout << typeid(a).name() << std::endl;

Upvotes: 18

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