_strtoui64, _wcstoui64
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_strtoui64, _wcstoui64

Convert a string to an unsigned __int64 value.

unsigned __int64 _strtoui64(
   const char *nptr,
   char **endptr,
   int base 
unsigned __int64 _wcstoui64(
   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

_strtoui64 returns the value represented in the string nptr, except when the representation would cause an overflow, in which case it returns _UI64_MAX. _strtoui64 will return 0 if no conversion can be performed.

_UI64_MAX is defined in LIMITS.H.

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


The _strtoui64 function converts nptr to an unsigned __int64. _wcstoui64 is a wide-character version of _strtoui64; its nptr argument is a wide-character string. Otherwise these functions behave identically.

Both functions stop reading the string nptr at the first character they 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.

Generic-Text Routine Mappings

TCHAR.H routine _UNICODE & _MBCS not defined _MBCS defined _UNICODE defined
_tcstoui64 _strtoui64 _strtoui64 _wstrtoui64

The current locale's LC_NUMERIC category setting 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.

_strtoui64 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.


Routine Required header Compatibility
_strtoui64 <stdlib.h> ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP
_wcstoui64 <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 Also

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

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