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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. If the specified name cannot be found, a null pointer is returned.

Consequently, if If the string returned by getenv() must be altered, a local copy should be created. Altering the string returned by getenv() results in undefined behavior . See also undefined behavior 184 of Annex J of the C Standard.

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Altering the string returned by setlocale() or the structure returned by localeconv() results in undefined behavior. See also undefined behaviors 120 and 121 of Annex J. Furthermore, the C Standard imposes no requirements on the contents of the string by setlocale(). Consequently, a program should make no assumptions can be made as to the string's internal contents or structure.

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Altering the string returned by strerror() results in undefined behavior. See also undefined behavior 184 of Annex J.

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