Question

I wrote this code because I’m having a similar problem in a larger program I’m writing. For all I know the problem is the same so I made this small example.

#include <stdio.h>

typedef struct
{
    int x;
    char * val;
}my_struct;

int main()
{
    my_struct me = {4, " "};
    puts("Initialization works.");
    me.val[0] = 'a';
    puts("Assignment works.");
    puts(me.val);
    puts("Output works.");
    return 0;
}

When compiled with tcc (Tiny C Compiler) it compiles and executes fine. But using GCC 4.6.0 20110513 (prerelease) it compiles, however, when I execute it I only get past “Initialization works.” before getting a segfault.

What am I doing wrong? Is it my code or my GCC compiler?

Answer 1

Your code. ANSI permits string constants to be read-only, and this is encouraged because it means they can be shared system-wide across all running instances of a program; gcc does so unless you specify -fwritable-strings, while tcc makes them writable (probably because it’s easier).