ctime, _ctime32, _ctime64, _wctime, _wctime32, _wctime64

项目
12/18/2017

The latest version of this topic can be found at ctime, _ctime32, _ctime64, _wctime, _wctime32, _wctime64.

Convert a time value to a string and adjust for local time zone settings. More secure versions of these functions are available; see ctime_s, _ctime32_s, _ctime64_s, _wctime_s, _wctime32_s, _wctime64_s.

Syntax

char *ctime(   
   const time_t *timer   
);  
char *_ctime32(   
   const __time32_t *timer )  
;  
char *_ctime64(   
   const __time64_t *timer )  
;  
wchar_t *_wctime(   
   const time_t *timer   
);  
wchar_t *_wctime32(   
   const __time32_t *timer  
);  
wchar_t *_wctime64(   
   const __time64_t *timer   
);

Parameters

timer
Pointer to stored time.

Return Value

A pointer to the character string result. NULL will be returned if:

time represents a date before midnight, January 1, 1970, UTC.
If you use _ctime32 or _wctime32 and time represents a date after 23:59:59 January 18, 2038, UTC.
If you use _ctime64 or _wctime64 and time represents a date after 23:59:59, December 31, 3000, UTC.

ctime is an inline function which evaluates to _ctime64 and time_t is equivalent to __time64_t. If you need to force the compiler to interpret time_t as the old 32-bit time_t, you can define _USE_32BIT_TIME_T. Doing this will cause ctime to evaluate to _ctime32. This is not recommended because your application may fail after January 18, 2038, and it is not allowed on 64-bit platforms.

Remarks

The ctime function converts a time value stored as a time_t value into a character string. The timer value is usually obtained from a call to time, which returns the number of seconds elapsed since midnight (00:00:00), January 1, 1970, coordinated universal time (UTC). The return value string contains exactly 26 characters and has the form:

Wed Jan 02 02:03:55 1980\n\0

A 24-hour clock is used. All fields have a constant width. The newline character ('\n') and the null character ('\0') occupy the last two positions of the string.

The converted character string is also adjusted according to the local time zone settings. See the time, _ftime, and localtime functions for information on configuring the local time and the _tzset function for details about defining the time zone environment and global variables.

A call to ctime modifies the single statically allocated buffer used by the gmtime and localtime functions. Each call to one of these routines destroys the result of the previous call. ctime shares a static buffer with the asctime function. Thus, a call to ctime destroys the results of any previous call to asctime, localtime, or gmtime.

_wctime and _wctime64 are the wide-character version of ctime and _ctime64; returning a pointer to wide-character string. Otherwise, _ctime64, _wctime, and _wctime64 behave identically to ctime.

These functions validate their parameters. If timer is a null pointer, or if the timer value is negative, these functions invoke the invalid parameter handler, as described in Parameter Validation. If execution is allowed to continue, the functions return NULL and set errno to EINVAL.

Generic-Text Routine Mappings

TCHAR.H routine	_UNICODE & _MBCS not defined	_MBCS defined	_UNICODE defined
`_tctime`	`ctime`	`ctime`	`_wctime`
`_tctime32`	`_ctime32`	`_ctime32`	`_wctime32`
`_tctime64`	`_ctime64`	`_ctime64`	`_wctime64`

Requirements

Routine	Required header
`ctime`	<time.h>
`_ctime32`	<time.h>
`_ctime64`	<time.h>
`_wctime`	<time.h> or <wchar.h>
`_wctime32`	<time.h> or <wchar.h>
`_wctime64`	<time.h> or <wchar.h>

For additional compatibility information, see Compatibility in the Introduction.

Example

// crt_ctime64.c  
// compile with: /W3  
/* This program gets the current  
 * time in _time64_t form, then uses ctime to  
 * display the time in string form.  
 */  
  
#include <time.h>  
#include <stdio.h>  
  
int main( void )  
{  
   __time64_t ltime;  
  
   _time64( &ltime );  
   printf( "The time is %s\n", _ctime64( &ltime ) ); // C4996  
   // Note: _ctime64 is deprecated; consider using _ctime64_s  
}

The time is Wed Feb 13 16:04:43 2002

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