errstr(2) [plan9 man page]

ERRSTR(2)							System Calls Manual							 ERRSTR(2)

NAME

       errstr, werrstr - description of last system call error

SYNOPSIS

       #include <u.h>
       #include <libc.h>

       int errstr(char *err)

       void werrstr(char *fmt, ...)

DESCRIPTION

       When  a	system	call  fails it returns -1 and records a string describing the error in a per-process buffer.  Errstr swaps the contents of
       that buffer with the contents of the array err.	Err should contain at least ERRLEN characters (defined in <libc.h>).  Usually errstr  will
       be  called  with an empty string, but the exchange property provides a mechanism for libraries to set the return value for the next call to
       errstr.

       If no system call has generated an error since the last call to errstr with an empty string, the result is an empty string.

       The verb r in print(2) calls errstr and outputs the error string.

       Werrstr takes a print style format as its argument and uses it to format a string to pass to errstr.  The string returned  from	errstr	is
       discarded.

SOURCE

       /sys/src/libc/9syscall
       /sys/src/libc/9sys/werrstr.c

DIAGNOSTICS

       Errstr always returns 0.

SEE ALSO

       intro(2), perror(2)

																	 ERRSTR(2)

STRTONUM(3)						   BSD Library Functions Manual 					       STRTONUM(3)

NAME

     strtonum -- reliably convert string value to an integer

SYNOPSIS

     #include <stdlib.h>

     long long
     strtonum(const char *nptr, long long minval, long long maxval, const char **errstr);

DESCRIPTION

     The strtonum() function converts the string in nptr to a long long value.	The strtonum() function was designed to facilitate safe, robust
     programming and overcome the shortcomings of the atoi(3) and strtol(3) family of interfaces.

     The string may begin with an arbitrary amount of whitespace (as determined by isspace(3)) followed by a single optional '+' or '-' sign.

     The remainder of the string is converted to a long long value according to base 10.

     The value obtained is then checked against the provided minval and maxval bounds.	If errstr is non-null, strtonum() stores an error string
     in *errstr indicating the failure.

RETURN VALUES

     The strtonum() function returns the result of the conversion, unless the value would exceed the provided bounds or is invalid.  On error, 0
     is returned, errno is set, and errstr will point to an error message.  On success, *errstr will be set to NULL; this fact can be used to dif-
     ferentiate a successful return of 0 from an error.

EXAMPLES

     Using strtonum() correctly is meant to be simpler than the alternative functions.

	   int iterations;
	   const char *errstr;

	   iterations = strtonum(optarg, 1, 64, &errstr);
	   if (errstr != NULL)
		   errx(1, "number of iterations is %s: %s", errstr, optarg);

     The above example will guarantee that the value of iterations is between 1 and 64 (inclusive).

ERRORS

     [ERANGE]		The given string was out of range.

     [EINVAL]		The given string did not consist solely of digit characters.

     [EINVAL]		The supplied minval was larger than maxval.

     If an error occurs, errstr will be set to one of the following strings:

     too large	The result was larger than the provided maximum value.
     too small	The result was smaller than the provided minimum value.
     invalid	The string did not consist solely of digit characters.

SEE ALSO

     atof(3), atoi(3), atol(3), atoll(3), sscanf(3), strtod(3), strtol(3), strtoul(3)

STANDARDS

     The strtonum() function is a BSD extension.  The existing alternatives, such as atoi(3) and strtol(3), are either impossible or difficult to
     use safely.

HISTORY

     The strtonum() function first appeared in OpenBSD 3.6.

BSD
								  April 29, 2004							       BSD