perror - print a system error message
void perror(const char *
const char * const
errno; /* Not really declared this way; see errno(3) */
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
sys_nerr: Since glibc 2.19: _DEFAULT_SOURCE Glibc 2.19 and earlier: _BSD_SOURCE
The perror() function produces a message on standard error describing the last error encountered during a call to a system or library function.
s is not NULL and
*s is not a null byte ('\0')), the argument string
s is printed, followed by a colon and a blank. Then an error message corresponding to the current value of
errno and a new-line.
To be of most use, the argument string should include the name of the function that incurred the error.
The global error list
sys_errlist, which can be indexed by
errno, can be used to obtain the error message without the newline. The largest message number provided in the table is
sys_nerr-1. Be careful when directly accessing this list, because new error values may not have been added to
sys_errlist. The use of
sys_errlist is nowadays deprecated; use strerror(3) instead.
When a system call fails, it usually returns -1 and sets the variable
errno to a value describing what went wrong. (These values can be found in
<errno.h>.) Many library functions do likewise. The function perror() serves to translate this error code into human-readable form. Note that
errno is undefined after a successful system call or library function call: this call may well change this variable, even though it succeeds, for example because it internally used some other library function that failed. Thus, if a failing call is not immediately followed by a call to perror(), the value of
errno should be saved.
errno: POSIX.1-2001, POSIX.1-2008, C89, C99, 4.3BSD.
sys_errlist derive from BSD, but are not specified in POSIX.1.
sys_errlist are defined by glibc, but in
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