_strtoui64, _wcstoui64, _strtoui64_l, _wcstoui64_l


The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.

The latest version of this topic can be found at _strtoui64, _wcstoui64, _strtoui64_l, _wcstoui64_l.

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   
unsigned __int64 _strtoui64_l(  
   const char *nptr,  
   char **endptr,  
   int base,  
   _locale_t locale  
unsigned __int64 _wcstoui64(  
   const wchar_t *nptr,  
   wchar_t **endptr,  
   int base,  
   _locale_t locale  


Null-terminated string to convert.

Pointer to character that stops scan.

Number base to use.

Locale to use.

_strtoui64 returns the value represented in the string nptr, except when the representation would cause an overflow, in which case it returns _UI64_MAX. _strtoui64will return 0 if no conversion can be performed.

_UI64_MAX is defined in LIMITS.H.

If nptr is NULL or the base is nonzero and either less than 2 or greater than 36, errno is set to EINVAL.

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

The _strtoui64function 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

The current locale's LC_NUMERIC category setting determines recognition of the radix character in nptr; for more information, see setlocale. The functions without the _l suffix use the current locale; _strtoui64_l and_wcstoui64_l are identical to the corresponding functions without the _l suffix except that they use the locale passed in instead. For more information, see Locale.

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. 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. The first character outside the range of the base stops the scan. For example, if base is 0 and the first character scanned is '0', an octal integer is assumed and an '8' or '9' character will stop the scan.

RoutineRequired header
_wcstoui64<stdlib.h> or <wchar.h>
_wcstoui64_l<stdlib.h> or <wchar.h>

For additional compatibility information, see Compatibility in the Introduction.

// crt_strtoui64.c  
#include <stdio.h>  
unsigned __int64 atoui64(const char *szUnsignedInt) {  
   return _strtoui64(szUnsignedInt, NULL, 10);  
int main() {  
   unsigned __int64 u = atoui64("18446744073709551615");  
   printf( "u = %I64u\n", u );  

u = 18446744073709551615  

Data Conversion
setlocale, _wsetlocale
String to Numeric Value Functions
strtod, _strtod_l, wcstod, _wcstod_l
strtoul, _strtoul_l, wcstoul, _wcstoul_l
atof, _atof_l, _wtof, _wtof_l