| STRERROR(3) | Library Functions Manual | STRERROR(3) | 
perror, strerror,
  strerror_r, sys_errlist,
  sys_nerr —
#include <stdio.h>
void
  
  perror(const
    char *string);
#include
  <errno.h>
extern const char * const sys_errlist[];
  
  extern const int sys_nerr;
#include
    <string.h>
char *
  
  strerror(int
    errnum);
int
  
  strerror_r(int
    errnum, char
    *strerrbuf, size_t
    buflen);
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. Note that in most cases the
    err(3) and
    warn(3) family of functions is
    preferable to perror(); they are more flexible and
    also print the program name.
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.
perror() and strerror()
  functions conform to ISO/IEC 9899:1999
  (“ISO C99”). The
  strerror_r() function conforms to
  IEEE Std 1003.1-2001 (“POSIX.1”).
perror() function first appeared in
  Version 4 AT&T UNIX. The
  strerror() function first appeared in
  4.3BSD-Reno. The strerror_r()
  function first appeared in NetBSD 4.0.
strerror() function will
  return its result in a static buffer which may be overwritten by subsequent
  calls.
The return type for strerror() is missing
    a type-qualifier; it should actually be const char
  *.
Programs that use the deprecated sys_errlist variable often fail to compile because they declare it inconsistently.
| May 9, 2015 | NetBSD 9.4 |