strerror
Synopsis
#include <string.h>
char *strerror(int errnum);
char *strerror_l(int errnum, locale_t locale);
int strerror_r(int errnum, char *strerrbuf, size_t buflen);
Status
Partially implemented
Conformance
IEEE Std 1003.1-2017
Description
The strerror() function shall map the error number in errnum to a locale-dependent error message string and shall
return a pointer to it. Typically, the values for errnum come from errno, but strerror() shall map any value of
type int to a message.
The application shall not modify the string returned. The returned string pointer might be invalidated, or the string
content might be overwritten by a subsequent call to strerror(), or by a subsequent call to strerror_l() in the same
thread. The returned pointer and the string content might also be invalidated if the calling thread is terminated.
The string may be overwritten by a subsequent call to strerror_l() in the same thread.
The contents of the error message strings returned by strerror() should be determined by the setting of the
LC_MESSAGES category in the current locale.
The implementation shall behave as if no function defined in this volume of POSIX.1-2017 calls strerror().
The strerror() and strerror_l() functions shall not change the setting of errno if successful.
Since no return value is reserved to indicate an error of strerror(), an application wishing to check for error
situations should set errno to 0, then call strerror(), then check errno. Similarly, since strerror_l() is
required to return a string for some errors, an application wishing to check for all error situations should set errno
to 0, then call strerror_l(), then check errno.
The strerror() function need not be thread-safe.
The strerror_l() function shall map the error number in errnum to a locale-dependent error message string in the
locale represented by locale and shall return a pointer to it.
The strerror_r() function shall map the error number in errnum to a locale-dependent error message string and shall
return the string in the buffer pointed to by strerrbuf, with length buflen.
If the value of errnum is a valid error number, the message string shall indicate what error occurred; if the value of errnum is zero, the message string shall either be an empty string or indicate that no error occurred; otherwise, if these functions complete successfully, the message string shall indicate that an unknown error occurred.
The behavior is undefined if the locale argument to strerror_l() is the special locale object LC_GLOBAL_LOCALE
or is not a valid locale object handle.
Return value
Upon completion, whether successful or not, strerror() shall return a pointer to the generated message string. On
error errno may be set, but no return value is reserved to indicate an error.
Upon successful completion, strerror_l() shall return a pointer to the generated message string. If errnum is not a
valid error number, errno may be set to [EINVAL], but a pointer to a message string shall still be returned. If any
other error occurs, errno shall be set to indicate the error and a null pointer shall be returned.
Upon successful completion, strerror_r() shall return 0. Otherwise, an error number shall be returned to indicate
the error.
Errors
These functions may fail if:
[EINVAL]The value of errnum is neither a valid error number nor zero.
The strerror_r() function may fail if:
[ERANGE]Insufficient storage was supplied via strerrbuf and buflen to contain the generated message string.
Tests
Tested
Known bugs
None