Reverse a c style string - runtime error -

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i've got code try reverse c-style string, getting runtime error , use figuring out why. thanks!

void switchedstr(char * str) {     char * end = str;     if (str) {         while (*end) {             ++end;         }         end--;     }     char temp;     while (end > str) {         temp = *str;         *str = *end;         *end = temp;         end--;         str++;     } }

if you're passing

char *str = "test123";

to switchedstr, give access violation, since such strings constant , compiler puts them in non-writable location (see section 6.4.5 of c99). if try modify it, you'd undefined behavior. however, if it's not constant string literal, it'd work, example 

char str[]="test123";

or

char *str = _strdup("test123");

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