STRTOUL(3) | Library Functions Manual | STRTOUL(3) |

`strtoul`

, `strtoull`

,
`strtoumax`

, `strtouq`

—
convert a string to an unsigned long, unsigned long long,
uintmax_t or uquad_t integer

library “libc”

```
#include
<stdlib.h>
```

`#include <limits.h>`

`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`);

`#include <inttypes.h>`

`uintmax_t`

`strtoumax`

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

`#include <sys/types.h>`

`#include <stdlib.h>`

`#include <limits.h>`

`u_quad_t`

`strtouq`

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

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 appropriate 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, the functions store
the address of the first invalid character in `*endptr`.
If there were no digits at all, however, the functions store the original
value of `nptr` in `*endptr`. (Thus,
if `*nptr` is not
‘`\0`

’ but
`**endptr` is ‘`\0`

’
on return, the entire string was valid.)

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`

,
`strtouq`

() returns `UQUAD_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 the
`base` argument is not supported then
`errno` is set to `EINVAL`

and the
functions return 0.

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

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).

atof(3), atoi(3), atol(3), atoll(3), strtod(3), strtoi(3), strtoimax(3), strtol(3), strtoll(3), strtou(3)

The `strtoul`

() function conforms to
ANSI X3.159-1989 (“ANSI C89”).
The `strtoull`

() and
`strtoumax`

() functions conform to
ISO/IEC 9899:1999
(“ISO C99”).

The `strtouq`

() function is a
BSD legacy function equivalent to
`strtoull`

() and should not be used in a new code.

Ignores the current locale.

April 30, 2015 | NetBSD-7.0.1 |