_itoa, _i64toa, _ui64toa, _itow, _i64tow, _ui64tow

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06/05/2017

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The latest version of this topic can be found at _itoa, _i64toa, _ui64toa, _itow, _i64tow, _ui64tow.

Converts an integer to a string. More secure versions of these functions are available; see _itoa_s, _i64toa_s, _ui64toa_s, _itow_s, _i64tow_s, _ui64tow_s.

Syntax

char *_itoa(  
   int value,  
   char *str,  
   int radix   
);  
char *_i64toa(  
   __int64 value,  
   char *str,  
   int radix   
);  
char * _ui64toa(  
   unsigned _int64 value,  
   char *str,  
   int radix   
);  
wchar_t * _itow(  
   int value,  
   wchar_t *str,  
   int radix   
);  
wchar_t * _i64tow(  
   __int64 value,  
   wchar_t *str,  
   int radix   
);  
wchar_t * _ui64tow(  
   unsigned __int64 value,  
   wchar_t *str,  
   int radix   
);  
template <size_t size>  
char *_itoa(  
   int value,  
   char (&str)[size],  
   int radix   
); // C++ only  
template <size_t size>  
char *_i64toa(  
   __int64 value,  
   char (&str)[size],  
   int radix   
); // C++ only  
template <size_t size>  
char * _ui64toa(  
   unsigned _int64 value,  
   char (&str)[size],  
   int radix   
); // C++ only  
template <size_t size>  
wchar_t * _itow(  
   int value,  
   wchar_t (&str)[size],  
   int radix   
); // C++ only  
template <size_t size>  
wchar_t * _i64tow(  
   __int64 value,  
   wchar_t (&str)[size],  
   int radix   
); // C++ only  
template <size_t size>  
wchar_t * _ui64tow(  
   unsigned __int64 value,  
   wchar_t (&str)[size],  
   int radix   
); // C++ only

Parameters

value
Number to be converted.

str
String result.

radix
Base of value; which must be in the range 2–36.

Return Value

Each of these functions returns a pointer to str. There is no error return.

Remarks

The _itoa, _i64toa, and _ui64toa functions convert the digits of the given value argument to a null-terminated character string and stores the result (up to 33 characters for _itoa and 65 for _i64toa and _ui64toa) in str. If radix equals 10 and value is negative, the first character of the stored string is the minus sign ( – ). _itow, _i64tow, and _ui64tow are wide-character versions of _itoa, _i64toa, and _ui64toa, respectively.

Important

To prevent buffer overruns, ensure that the str buffer is large enough to hold the converted digits plus the trailing null-character and a sign character.

In C++, these functions have template overloads that invoke the newer, secure counterparts of these functions. For more information, see Secure Template Overloads.

Generic-Text Routine Mappings

Tchar.h routine	_UNICODE and _MBCS not defined	_MBCS defined	_UNICODE defined
`_itot`	`_itoa`	`_itoa`	`_itow`
`_i64tot`	`_i64toa`	`_i64toa`	`_i64tow`
`_ui64tot`	`_ui64toa`	`_ui64toa`	`_ui64tow`

Requirements

Routine	Required header
`_itoa`	<stdlib.h>
`_i64toa`	<stdlib.h>
`_ui64toa`	<stdlib.h>
`_itow`	<stdlib.h>
`_i64tow`	<stdlib.h>
`_ui64tow`	<stdlib.h>

For more compatibility information, see Compatibility in the Introduction.

Example

// crt_itoa.c  
// compile with: /W3  
// This program makes use of the _itoa functions  
// in various examples.  
  
#include <string.h>  
#include <stdlib.h>  
  
int main( void )  
{  
   char buffer[65];  
   int r;  
   for( r=10; r>=2; --r )  
   {  
     _itoa( -1, buffer, r ); // C4996  
     // Note: _itoa is deprecated; consider using _itoa_s instead  
     printf( "base %d: %s (%d chars)\n", r, buffer, strnlen(buffer, _countof(buffer)) );  
   }  
   printf( "\n" );  
   for( r=10; r>=2; --r )  
   {  
     _i64toa( -1L, buffer, r ); // C4996  
     // Note: _i64toa is deprecated; consider using _i64toa_s  
     printf( "base %d: %s (%d chars)\n", r, buffer, strnlen(buffer, _countof(buffer)) );  
   }  
   printf( "\n" );  
   for( r=10; r>=2; --r )  
   {  
     _ui64toa( 0xffffffffffffffffL, buffer, r ); // C4996  
     // Note: _ui64toa is deprecated; consider using _ui64toa_s  
     printf( "base %d: %s (%d chars)\n", r, buffer, strnlen(buffer, _countof(buffer)) );  
   }  
}

base 10: -1 (2 chars)  
base 9: 12068657453 (11 chars)  
base 8: 37777777777 (11 chars)  
base 7: 211301422353 (12 chars)  
base 6: 1550104015503 (13 chars)  
base 5: 32244002423140 (14 chars)  
base 4: 3333333333333333 (16 chars)  
base 3: 102002022201221111210 (21 chars)  
base 2: 11111111111111111111111111111111 (32 chars)  
  
base 10: -1 (2 chars)  
base 9: 145808576354216723756 (21 chars)  
base 8: 1777777777777777777777 (22 chars)  
base 7: 45012021522523134134601 (23 chars)  
base 6: 3520522010102100444244423 (25 chars)  
base 5: 2214220303114400424121122430 (28 chars)  
base 4: 33333333333333333333333333333333 (32 chars)  
base 3: 11112220022122120101211020120210210211220 (41 chars)  
base 2: 1111111111111111111111111111111111111111111111111111111111111111 (64 chars)  
  
base 10: 18446744073709551615 (20 chars)  
base 9: 145808576354216723756 (21 chars)  
base 8: 1777777777777777777777 (22 chars)  
base 7: 45012021522523134134601 (23 chars)  
base 6: 3520522010102100444244423 (25 chars)  
base 5: 2214220303114400424121122430 (28 chars)  
base 4: 33333333333333333333333333333333 (32 chars)  
base 3: 11112220022122120101211020120210210211220 (41 chars)  
base 2: 1111111111111111111111111111111111111111111111111111111111111111 (64 chars)

.NET Framework Equivalent

System::Convert::ToString

共用方式為