CODEWITHSUNDEEP
cstringgccvariable-assignmenttcc
Tnelsond
Tnelsond

Reputation: 45

Gcc compiler C string assignment issue

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?

Upvotes: 0

Views: 1348

Answers (3)

sverre
sverre

Reputation: 6919

As other answers have pointed out, val is pointing at a string constant. Try

my_struct me = {4, malloc(2)};

and remember to check if val is NULL if you're using this in a real program.

Upvotes: 0

Mahesh
Mahesh

Reputation: 34655

val is an points to read only location.

char *readOnly = "Data in read only location" ;

readOnly pointing data cannot be modified.

Upvotes: 0

geekosaur
geekosaur

Reputation: 61457

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).

Upvotes: 8

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