strtoul - Convert a string into a whole number (unsigned long int)

Definition

#include <stdlib.h>

unsigned long int strtoul(const char *s, char **p, int base);

strtoul converts a string to which s points into an integer of type unsigned long int.
The string to be converted may be structured as follows:

[{tab | 'BLANK' } ...][0 | 0X]digit...

All control characters for white space may be used for tab (see definition under isspace).

Depending on the base (see base), the digits 0 to 9 and the letters a (or A) to z (or Z) may be used for digit.

strtoul also recognizes strings that start with convertible digits (including octal and hexadecimal digits) but then end with any character. In such cases, strtoul first truncates the numeric part and converts it.

strtoul additionally provides a pointer (*p) to the first non-convertible character in string s via the second argument p of type char **. However, this occurs only if p is not passed as a NULL pointer.

A third argument, base, defines the base (e.g. decimal, octal or hexadecimal) for the conversion.

Parameters

const char *s

Pointer to the string to be converted.

char **p

A pointer (*p) to the first character in s that terminates the conversion is returned if p is not a NULL pointer.
If no conversion is possible at all, *p is set to the start address of string s.

int base

Integer from 0 to 36, which is to be used as the base for the computation.

From base 11 to base 36, letters a (or A) to z (or Z) in the string to be converted are assumed to be digits with the corresponding values 10 (a/A) to 35 (z/Z).

If base is equal to 0, the base will be determined from the structure of string s as shown below:

leading 0	base 8
leading 0X or 0x	base 16
otherwise	base 10

If the parameter base = 16 is used for calculations, the characters 0X and 0x in string s are ignored.

Return val.

Integer value of type unsigned long

for strings that have a structure as described above and represent a numeric value.

0

for strings that do not conform to the syntax described above. No conversion is performed.
If the value of base is not supported, errno is set to EINVAL.

ULONG_MAX

if the result overflows, errno is set to ERANGE (result too large).

See also

atol, atoll, atoi, strtol, strtoll, stroull, wcstol, wcstoll, wcstoul, wcstoull