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Some functions return a pointer to an object that cannot be modified without causing undefined behavior. These functions include the standard getenv(), setlocale(), localeconv(), and strerror() functions. In such cases, the function call results must be treated as being const qualified.

Subclause 7.22.4.6, paragraph 4, of the C Standard [ISO/IEC 9899:2011] defines getenv() as follows:

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Similarly, subclause 7.11.1.1 paragraph 1, paragraph 8 [ISO/IEC 9899:2011], defines setlocale() as follows:

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.

 And subclause 7.11.1.2, paragraph 8 [ISO/IEC 9899:2011], defines localeconv() as follows:

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Finally, subclause 7.24.6.2, paragraph 4 [ISO/IEC 9899:2011], states:

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

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Bibliography

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