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PERROR(3) Library functions PERROR(3)
perror - print a system error message
void perror(const char *s);
const char *sys_errlist;
The routine perror() produces a message on the standard error output, describing the last
error encountered during a call to a system or library function. First (if s is not NULL
and *s is not NUL) the argument string s is printed, followed by a colon and a blank.
Then the message and a new-line.
To be of most use, the argument string should include the name of the function that
incurred the error. The error number is taken from the external variable errno, which is
set when errors occur but not cleared when non-erroneous calls are made.
The global error list sys_errlist indexed by errno can be used to obtain the error mes-
sage 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.
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 library 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.
ANSI C, BSD 4.3, POSIX, X/OPEN
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