MirBSD manpage: strtonum(3)

STRTONUM(3)                BSD Programmer's Manual                 STRTONUM(3)


     strtonum - reliably convert string value to an integer


     #include <stdlib.h>
     #include <limits.h>

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


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

     The string may begin with an arbitrary amount of whitespace (as deter-
     mined 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. On MirBSD, if the value is prefixed by '0' or '0x', conver-
     sion is done according to base 8 or 16, respectively. This is a change in
     the underlying library and only visible to the user, not to the program
     using strtonum().

     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.


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


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

           int iterations;
           const char *errstr;

           iterations = strtonum(optarg, 1, 64, &errstr);
           if (errstr)
                   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.


     [ERANGE]      The given string was out of range.

     [EINVAL]      The given string did not consist solely of digit charac-

     [EINVAL]      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.


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


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


     The strtonum() function first appeared in OpenBSD 3.6.

MirBSD #10-current              April 29, 2004                               1

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