PERROR(3) - Linux man page online | Library functions

Print a system error message.

PERROR(3) Linux Programmer's Manual PERROR(3)


perror - print a system error message


#include <stdio.h> void perror(const char *s); #include <errno.h> const char * const sys_errlist[]; int sys_nerr; int errno; /* Not really declared this way; see errno(3) */ Feature Test Macro Requirements for glibc (see feature_test_macros(7)): sys_errlist, 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. First (if 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 cur‐ rent 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 func‐ tions 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 exam‐ ple because it internally used some other library function that failed. Thus, if a fail‐ ing call is not immediately followed by a call to perror(), the value of errno should be saved.


For an explanation of the terms used in this section, see attributes(7). ┌──────────┬───────────────┬─────────────────────┐ │Interface │ Attribute │ Value │ ├──────────┼───────────────┼─────────────────────┤ │perror() │ Thread safety │ MT-Safe race:stderr │ └──────────┴───────────────┴─────────────────────┘


perror(), errno: POSIX.1-2001, POSIX.1-2008, C89, C99, 4.3BSD. The externals sys_nerr and sys_errlist derive from BSD, but are not specified in POSIX.1.


The externals sys_nerr and sys_errlist are defined by glibc, but in <stdio.h>.


err(3), errno(3), error(3), strerror(3)


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2017-09-15 PERROR(3)
This manual Reference Other manuals
perror(3) referred by af_error(3) | aufs(5) | err(3) | errc(3bsd) | errno(2freebsd) | errno(3) | error(3) | errormsg(3pub) | explain(3) | explain_lca2010(1) | fmtmsg(3) | genders_errnum(3) | guestfs-hacking(1) | guestfs-release-notes(1) | intro(2freebsd) | lam-helpfile(5) | pmErrStr(3) | psignal(3) | pvm_perror(3PVM) | rmt-dump(8)
refer to attributes(7) | err(3) | errno(3) | error(3) | feature_test_macros(7) | strerror(3)
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