Why does *(str+i) = *(str +j) not work here?

Question

void reverse(char *str){
    int i,j;
    char temp;
    for(i=0,j=strlen(str)-1; i<j; i++, j--){
     temp = *(str + i);
     *(str + i) = *(str + j);
     *(str + j) = temp;
     printf("%c",*(str + j));
    }
}



int main (int argc, char const *argv[])
{
    char *str = "Shiv";
    reverse(str);
    printf("%s",str);
    return 0;
}

When I use char *str = "Shiv" the lines in the swapping part of my reverse function i.e str[i]=str[j] dont seem to work, however if I declare str as char str[] = "Shiv", the swapping part works? What is the reason for this. I was a bit puzzled by the behavior, I kept getting the message "Bus error" when I tried to run the program.

Answer 1

When you use char *str = "Shiv";, you don't own the memory pointed to, and you're not allowed to write to it. The actual bytes for the string could be a constant inside the program's code.

When you use char str[] = "Shiv";, the 4(+1) char bytes and the array itself are on your stack, and you're allowed to write to them as much as you please.