strtoul - convert string to unsigned long integer

Syntax

#include <stdlib.h>

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

Description

The string to be converted may be structured as follows:

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

Any white-space character 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 begin with convertible digits (including octal and hexadecimal digits) but end with some other characters. In such cases, strtoul() truncates the numeric part before converting it.

strtoul() returns a pointer to the first non-convertible character in string s via the second argument endptr of type char **, but only if endptr is not passed as a null pointer.

If no conversion is possible at all, *endptr is set to the start address of string s.

A third argument, base, defines the base (e.g. decimal, octal or hexadecimal) for the conversion. base may be any integer from 0 to 36.

For base 11 to base 36, the letters a (or A) to z (or Z) in the string to be converted are assumed to be digits, with corresponding values from 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 or 0x in string s will be ignored.

Return val.

Integer value of type unsigned long

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

0

for strings that do not conform to the syntax described above.

ULONG_MAX

if an overflow occurs; errno is set to indicate the error.

Errors

strtoul() will fail if:

 

EINVAL

The value of base is not supported.

 

ERANGE

The return value causes an overflow.

 

EINVAL

The conversion could not be performed.

See also

atol(), atoi(), isalpha(), strtol(), stdlib.h.