C in a Nutshell

Name

strtoul, strtoull

Synopsis

Converts a string into an unsigned long (or unsigned long long) integer value

#include <stdlib.h>
unsigned longstrtoul( const char * restrict s, char ** restrict endptr,
                       int base );
unsigned long long strtoull(  const char  *  restrict s, char ** restrict endptr,
                             int base );        (C99)

The strtoul() function attempts to interpret the string addressed by its first pointer argument, s, as an integer numeric value, and returns the result with the type unsigned long. Otherwise, the strtoul() function works in the same way as strtol(). strtoull() is similar, but returns unsigned long long.

If the resulting value is outside the range of the function’s type, then the return value is ULONG_MAX (or ULLONG_MAX, for strtoull()), and the errno variable is set to the value of ERANGE (“range error”).

Example

This for loop uses stroul() to convert an IPv4 address from a dotted-decimal string to a 32-bit integer value:

char dotted[ ] = "172.16.2.10", *ptr = dotted, *nextdot = NULL;
unsigned long dest = 0;
for ( i = 0; i < 4; i++)
{
  dest << 8;
  dest +=stroul( ptr, &nextdot, 10 );
  ptr = nextdot + 1;
}

See Also

strtol(), strtod(), strtof(), and strtold(); wcstol() and wcstoul(); strtoimax(), strtoumax(), wcstoimax(), and wcstoumax()