replacing character in a pointer to char array

Question

Okay so I just want to know why my program keeps crashing, all im trying to do is loop through the pointer to a char array and replace the old character with the new one and return how many times I have replaced it:

int main(void) { 
   char *s = "hello";    
   printf("%lu\n",str_replace_all(s,'e','f')); 
   printf("%s",s); 
   return 0; 
} 

size_t str_replace_all(char *s,int oldc,int newc) { 
    size_t count = 0; 
    for(;*s != '\0'; s++) { 
       if(*s == oldc) { 
       *s = newc; 
        count++
    }
}
    return count; 
}

This compiles fine with gcc -ansi -W -Wall -pedantic but when i run it it crashes with this: Segmentation fault (core dumped) I need help figuring out whats going on, Thanks!

P.S expected output was hfllo

@Manish Mallavarapu Take into account that you have to declare the function before its call for example before main and include header stdio.h — Vlad from Moscow, Jul 26 '15 at 08:03

score 3 · Accepted Answer · answered Jul 26 '15 at 07:50

3

You're trying to modify a literal string, which produces undefined behavior. Change the declaration to:

char s[] = "hello";

answered Jul 26 '15 at 07:50

Barmar

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thanks! that was an easy solution – Manish Mallavarapu Jul 26 '15 at 07:53
Is the unrefined behaviour because string literal is const type? – Tahlil Jul 26 '15 at 07:55
2

@Tahlil In C string literals have types of non-constant character arrays. Nevertheless the C Standard does not allow to change string literals.. In C++ string literals indeed have types of constant character arrays. – Vlad from Moscow Jul 26 '15 at 08:00

score 0 · Answer 2 · answered Jul 26 '15 at 09:05

The reason why you are getting a segmentation fault is that there is no memory allocated for the variable s. It is just a pointer pointing to some address location. Possible solution is char s[] = "hello" or you can allocate some memory in heap and memcpy or strcpy "hello" to the char pointer. Then you code will work. Hope it clears the concept. :)

replacing character in a pointer to char array

2 Answers2