Modifying C string constants? -

possible duplicate:
why segmentation fault when writing string?

i want write function reverses given string passed it. but, can not. if supply doreverse function (see code below) character array, code works well.

i can't figure out why not work. able access str[0] in doreverse, can't change value of array using char pointer. ideas?

void doreverse(char *str) {     str[0] = 'b'; }  void main(void) {     char *str = "abc";     doreverse(str);     puts(str); } 

update:

i know how write reverse function passing character array it:

void reverse1(char p[]) {     int i, temp, y;      (i = 0, y = strlen(p); < y; ++i, --y) {         temp = p[y-1];         p[y-1] = p[i];         p[i] = temp;     } } 

but, want write version gets char pointer parameter.

the simplest solution change declaration of str to

char str[] = "abc"; 

this makes str array of char initialized string "abc". have str pointer-to-char initialized point string described string literal. there key difference: string literals read-only give compiler maximum flexibility on store them; ub modify them. arrays of char mutable, , it's okay modify those.

ps. main() returns int.