July 23, 2009 STRTOUL 3

### NAME

strtoul, strtoull, strtoumax, strtouq - convert a string to an unsigned long, unsigned long long, uintmax_t or uquad_t integer

### LIBRARY

Standard C Library (libc, -lc)

### SYNOPSIS

```unsigned` `long` `int` strtoul(```const char * restrict nptr``, char ** restrict endptr``, int base`)
```unsigned` `long` `long` `int` strtoull(```const char * restrict nptr``, char ** restrict endptr``, int base`)

```uintmax_t` strtoumax(```const char * restrict nptr``, char ** restrict endptr``, int base`)

```u_quad_t` strtouq(```const char * restrict nptr``, char ** restrict endptr``, int base`)

### DESCRIPTION

The strtoul(``) function converts the string in ```nptr` to an unsigned long int value. The strtoull(``) function converts the string in ```nptr` to an unsigned long long int value. The strtoumax(``) function converts the string in ```nptr` to an uintmax_t value. The strtouq(``) function converts the string in ```nptr` to a u_quad_t value. The conversion is done according to the given ```base`, which must be between 2 and 36 inclusive, or be the special value 0.

The string may begin with an arbitrary amount of white space (as determined by isspace(3)) followed by a single optional `+' or `-' sign. If ```base` is zero or 16, the string may then include a `0x' prefix, and the number will be read in base 16; otherwise, a zero ```base` is taken as 10 (decimal) unless the next character is `0', in which case it is taken as 8 (octal).

The remainder of the string is converted to an unsigned long value in the obvious manner, stopping at the end of the string or at the first character that does not produce a valid digit in the given base. (In bases above 10, the letter `A' in either upper or lower case represents 10, `B' represents 11, and so forth, with `Z' representing 35.)

If ```endptr` is non nil, strtoul(``) stores the address of the first invalid character in ```*endptr`. If there were no digits at all, however, strtoul(``) stores the original value of ```nptr` in ```*endptr`. (Thus, if ```*nptr` is not `\0' but ```**endptr` is `\0' on return, the entire string was valid.)

### RETURN VALUES

The strtoul(``) function returns either the result of the conversion or, if there was a leading minus sign, the negation of the result of the conversion, unless the original (non-negated) value would overflow; in the latter case, strtoul(``) returns ```ULONG_MAX`, strtoull(``) returns ```ULLONG_MAX`, strtoumax(``) returns ```UINTMAX_MAX`, and the global variable errno is set to ```ERANGE`.

There is no way to determine if strtoul(``) has processed a negative number (and returned an unsigned value) short of examining the string in ```nptr` directly.

If no error occurs, errno is left unchanged. This behavior (which is unlike most library functions) is guaranteed by the pertinent standards.

### EXAMPLES

Because the return value of strtoul(``) cannot be used unambiguously to detect an error, errno is left unchanged after a successful call. To ensure that a string is a valid number (i.e., in range and containing no trailing characters), clear errno beforehand explicitly, then check it afterwards:

  `

      char *ep;
      unsigned long ulval;

      ...

      errno = 0;
      ulval = strtoul(buf, &ep, 10);
      if (buf[0] == '\0' || *ep != '\0')
              goto not_a_number;
      if (errno == ERANGE && ulval == ULONG_MAX)
              goto out_of_range;

  `

This example will accept ``12'' but not ``12foo'' or ``12\n''. If trailing whitespace is acceptable, further checks must be done on *ep; alternately, use sscanf(3).

### ERRORS

[```ERANGE`]
  The given string was out of range; the value converted has been clamped.

### SEE ALSO

strtoimax(3), strtol(3), strtoll(3)

### STANDARDS

The strtoul(``) function conforms to ANSI X3.159-1989 (``ANSI C89'') . The strtoull(``) and strtoumax(``) functions conform to ISO/IEC 9899:1999 (``ISO C99'') .

### BUGS

Ignores the current locale.