STRERROR(3) Library Functions Manual STRERROR(3)

strerror strerror_r — get error message string

#include <string.h>

char *strerror(int errnum);
[TSF] int strerror_r(int errnum, char *strerrbuf, size_t buflen);

For strerror (): [CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 (“POSIX.1”) defers to the ISO C standard.

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 to a message.

The string pointed to shall not be modified by the application, but may be overwritten by a subsequent call to strerror () [CX] or perror(3).

[CX] The contents of the error message strings returned by strerror () should be determined by the setting of the category in the current locale.

The implementation shall behave as if no function defined in this volume of IEEE Std 1003.1-2001 (“POSIX.1”) calls strerror ().

[CX] The strerror () function shall not change the setting of errno if successful.

Since no return value is reserved to indicate an error, an application wishing to check for error situations should set errno to 0, then call strerror (), then check errno.

The strerror () function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.

[TSF] 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 , with length .

Upon successful completion, 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.

[TSF] Upon successful completion, strerror_r () shall return 0. Otherwise, an error number shall be returned to indicate the error.

These functions may fail if:

The value of errnum is not a valid error number.

The strerror_r () function may fail if:

[TSF] Insufficient storage was supplied via strerrbuf and buflen to contain the generated message string.

None.

None.

None.

None.

perror(3), the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <string.h>

First released in Issue 3.

The DESCRIPTION is updated to indicate that errno is not changed if the function is successful.

A note indicating that this function need not be reentrant is added to the DESCRIPTION.

Extensions beyond the ISO C standard are marked.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

  • In the RETURN VALUE section, the fact that errno may be set is added.
  • The [EINVAL] optional error condition is added.

The DESCRIPTION is updated to avoid use of the term "must" for application requirements.

The strerror_r () function is added in response to IEEE PASC Interpretation 1003.1c #39.

The strerror_r () function is marked as part of the Thread-Safe Functions option.

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December 6, 2001 posix.fail