Where in memory are string literals ? stack / heap

问题:

Possible Duplicate:
C String literals: Where do they go?

As far as I know,

generally, pointer have to be allocated by malloc(), and will be allocated to heap, then unallocated by free();

and

non pointer(int,char,float,etc..) will be allocated automatically to stack, and unallocated as long as the function go to return

but, from following code :

#include <stdio.h>

int main()
{
char *a;

a = "tesaja";

return 0;
}

where will a allocated to ? stack or heap ?

回答1:

The string literal will be allocated in data segment. The pointer to it, a, will be allocated on the stack.

Your code will eventually get transformed by the compiler into something like this:

#include <stdio.h>

const static char literal_constant_34562[7] = {'t', 'e', 's', 'a', 'j', 'a', '\0'};

int main()
{
    char *a;

    a = &literal_constant_34562[0];

    return 0;
}

Therefore, the exact answer to your question is: neither. Stack, data, bss and heap are all different regions of memory. Const static initialized variables will be in data.

回答2:

a itself (the pointer) is defined as a local variable (implicitly) using the auto storage class, so it's allocated on the stack (or whatever memory the implementation uses for stack-like allocation -- some machines, such as IBM mainframes and the first Crays, don't have a "stack" in the normal sense).

The string literal "tesaja" is allocated statically. Exactly where that will be depends on the implementation -- some put it with other data, and some put it in a read-only data segment. A few treat all data as read/write and all code as read-only. Since they want they string literal to be read-only, they put it in the code segment.