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strtoul, wcstoul

Convert strings to an unsigned long-integer value.

unsigned long strtoul(
   const char *nptr,
   char **endptr,
   int base 
unsigned long wcstoul(
   const wchar_t *nptr,
   wchar_t **endptr,
   int base 


Null-terminated string to convert.
Pointer to character that stops scan.
Number base to use.

Return Value

strtoul returns the converted value, if any, or ULONG_MAX on overflow. strtoul returns 0 if no conversion can be performed. wcstoul returns values analogously to strtoul. For both functions, errno is set to ERANGE if overflow or underflow occurs.

See _doserrno, errno, _sys_errlist, and _sys_nerr for more information on this, and other, return codes.


Each of these functions converts the input string nptr to an unsigned long.

strtoul stops reading the string nptr at the first character it cannot recognize as part of a number. This may be the terminating null character, or it may be the first numeric character greater than or equal to base. The LC_NUMERIC category setting of the current locale determines recognition of the radix character in nptr; for more information, see setlocale. If endptr is not NULL, a pointer to the character that stopped the scan is stored at the location pointed to by endptr. If no conversion can be performed (no valid digits were found or an invalid base was specified), the value of nptr is stored at the location pointed to by endptr.

wcstoul is a wide-character version of strtoul; its nptr argument is a wide-character string. Otherwise these functions behave identically.

Generic-Text Routine Mappings

TCHAR.H routine _UNICODE & _MBCS not defined _MBCS defined _UNICODE defined
_tcstoul strtoul strtoul wcstoul

strtoul expects nptr to point to a string of the following form:

[whitespace] [{+ | }] [0 [{ x | X }]] [digits]

A whitespace may consist of space and tab characters, which are ignored; digits are one or more decimal digits. The first character that does not fit this form stops the scan. If base is between 2 and 36, then it is used as the base of the number. If base is 0, the initial characters of the string pointed to by nptr are used to determine the base. If the first character is 0 and the second character is not 'x' or 'X', the string is interpreted as an octal integer; otherwise, it is interpreted as a decimal number. If the first character is '0' and the second character is 'x' or 'X', the string is interpreted as a hexadecimal integer. If the first character is '1' through '9', the string is interpreted as a decimal integer. The letters 'a' through 'z' (or 'A' through 'Z') are assigned the values 10 through 35; only letters whose assigned values are less than base are permitted. strtoul allows a plus (+) or minus () sign prefix; a leading minus sign indicates that the return value is negated.


Routine Required header Compatibility
strtoul <stdlib.h> ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP
wcstoul <stdlib.h> or <wchar.h> ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP

For additional compatibility information, see Compatibility in the Introduction.


All versions of the C run-time libraries.


See the example for strtod.

See Also

Data Conversion Routines, Locale Routines | strtod Functions Overview | strtod | strtol | atof | localeconv | setlocale | Run-Time Routines and .NET Framework Equivalents