c - Confusion with Pointers Increment -

char *str = "string" ; char *end = str; while(*(end+1) != '\0') {     end++; }  while(str < end) {     char temp = *str;     *str = *end;     *end = temp;     str++;     end--; }` 

edit: both these*str = *end, *str++ = *end invalid?

the above code gives error @ line.

aren't str , end pointing read part in memory whether post increment?

char *str = "string" ; 

is string literal placed in read-only data section.

in line:

*str = *end; 

is trying modify string, segfault..

same *str++ = *end, both invalid.

to make code work, change

char *str = "string"; 

to

char str[] = "string"; 

but note can not use *str++ because array names constant (not modifiable lvalue)