Modifying the string returned by getenv strerror and setlocale functions

Modifying the strings returned by the standard functions getenv(), strerror() and setlocale() is undefined. So, implementations may use static storage for these strings.

The getenv() function, C11, §7.22.4.7, 4, says:

The getenv function returns a pointer to a string associated with the matched list member. The string pointed to shall not be modified by the program, but may be overwritten by a subsequent call to the getenv function.

The strerror() function, C11, §7.23.6.3, 4 says:

The strerror function returns a pointer to the string, the contents of which are localespecific. The array pointed to shall not be modified by the program, but may be overwritten by a subsequent call to the strerror function.

The setlocale() function, C11, §7.11.1.1, 8 says:

The pointer to string returned by the setlocale function is such that a subsequent call with that string value and its associated category will restore that part of the program’s locale. The string pointed to shall not be modified by the program, but may be overwritten by a subsequent call to the setlocale function.

Similarly the localeconv() function returns a pointer to struct lconv which shall not be modified.

The localeconv() function, C11, §7.11.2.1, 8 says:

The localeconv function returns a pointer to the filled-in object. The structure pointed to by the return value shall not be modified by the program, but may be overwritten by a subsequent call to the localeconv function.