.\" Copyright (c) 2004 Ted Unangst .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR .\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES .\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. .\" .\" $OpenBSD: strtonum.3,v 1.13 2006/04/25 05:15:42 tedu Exp $ .\" $FreeBSD$ .\" .Dd April 29, 2004 .Dt STRTONUM 3 .Os .Sh NAME .Nm strtonum .Nd "reliably convert string value to an integer" .Sh SYNOPSIS .In stdlib.h .Ft long long .Fo strtonum .Fa "const char *nptr" .Fa "long long minval" .Fa "long long maxval" .Fa "const char **errstr" .Fc .Sh DESCRIPTION The .Fn strtonum function converts the string in .Fa nptr to a .Vt "long long" value. The .Fn strtonum function was designed to facilitate safe, robust programming and overcome the shortcomings of the .Xr atoi 3 and .Xr strtol 3 family of interfaces. .Pp The string may begin with an arbitrary amount of whitespace (as determined by .Xr isspace 3 ) followed by a single optional .Ql + or .Ql - sign. .Pp The remainder of the string is converted to a .Vt "long long" value according to base 10. .Pp The value obtained is then checked against the provided .Fa minval and .Fa maxval bounds. If .Fa errstr is non-null, .Fn strtonum stores an error string in .Fa *errstr indicating the failure. .Sh RETURN VALUES The .Fn strtonum function returns the result of the conversion, unless the value would exceed the provided bounds or is invalid. On error, 0 is returned, .Va errno is set, and .Fa errstr will point to an error message. On success, .Fa *errstr will be set to .Dv NULL ; this fact can be used to differentiate a successful return of 0 from an error. .Sh EXAMPLES Using .Fn strtonum correctly is meant to be simpler than the alternative functions. .Bd -literal -offset indent int iterations; const char *errstr; iterations = strtonum(optarg, 1, 64, &errstr); if (errstr != NULL) errx(1, "number of iterations is %s: %s", errstr, optarg); .Ed .Pp The above example will guarantee that the value of iterations is between 1 and 64 (inclusive). .Sh ERRORS .Bl -tag -width Er .It Bq Er ERANGE The given string was out of range. .It Bq Er EINVAL The given string did not consist solely of digit characters. .It Bq Er EINVAL The supplied .Fa minval was larger than .Fa maxval . .El .Pp If an error occurs, .Fa errstr will be set to one of the following strings: .Pp .Bl -tag -width ".Li too large" -compact .It Li "too large" The result was larger than the provided maximum value. .It Li "too small" The result was smaller than the provided minimum value. .It Li invalid The string did not consist solely of digit characters. .El .Sh SEE ALSO .Xr atof 3 , .Xr atoi 3 , .Xr atol 3 , .Xr atoll 3 , .Xr sscanf 3 , .Xr strtod 3 , .Xr strtol 3 , .Xr strtoul 3 .Sh STANDARDS The .Fn strtonum function is a .Bx extension. The existing alternatives, such as .Xr atoi 3 and .Xr strtol 3 , are either impossible or difficult to use safely. .Sh HISTORY The .Fn strtonum function first appeared in .Ox 3.6 .