The
strerror(),
strerror_r(), and
perror() functions look up the language-dependent error message string corresponding to an error number.
The
strerror() function accepts an error number argument
errnum and returns a pointer to the corresponding message string.
The
strerror_r() function renders the same result into
strerrbuf for a maximum of
buflen characters and returns 0 upon success.
The
perror() function finds the error message corresponding to the current value of the global variable
errno (
intro(2)) and writes it, followed by a newline, to the standard error file descriptor. If the argument
string is non-
NULL and does not point to the nul character, this string is prepended to the message string and separated from it by a colon and space (“
: ”); otherwise, only the error message string is printed.
If the error number is not recognized, these functions pass an error message string containing “
Unknown error: ” followed by the error number in decimal. To warn about this,
strerror() sets
errno to
EINVAL, and
strerror_r() returns
EINVAL. Error numbers recognized by this implementation fall in the range 0 <
errnum <
sys_nerr.
If insufficient storage is provided in
strerrbuf (as specified in
buflen) to contain the error string,
strerror_r() returns
ERANGE and
strerrbuf will contain an error message that has been truncated and
NUL terminated to fit the length specified by
buflen.
The message strings can be accessed directly using the external array
sys_errlist. The external value
sys_nerr contains a count of the messages in
sys_errlist. The use of these variables is deprecated;
strerror() or
strerror_r() should be used instead.