Synopsis

#include <time.h>

char *asctime(const struct tm *timeptr);

char *asctime_r(const struct tm *restrict tm, char *restrict buf);

Status

Partially implemented

Conformance

IEEE Std 1003.1-2017

Description

The asctime() function shall convert the broken-down time in the structure pointed to by timeptr into a string in the form:

Sun Sep 16 01:03:52 1973\n\0

using the equivalent of the following algorithm:

char *asctime(const struct tm *timeptr)
{
    static char wday_name[7][3] = {
        "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
    };
    static char mon_name[12][3] = {
        "Jan", "Feb", "Mar", "Apr", "May", "Jun",
        "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
    };
    static char result[26];

    sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
        wday_name[timeptr->tm_wday],
        mon_name[timeptr->tm_mon],
        timeptr->tm_mday,` `timeptr->tm_hour,
        timeptr->tm_min,` `timeptr->tm_sec,
        1900 + `timeptr->tm_year);
    return result;
}

However, the behavior is undefined if timeptr->tm_wday or timeptr->tm_mon are not within the normal ranges as defined in <time.h>, or if timeptr->tm_year exceeds INT_MAX-1990, or if the above algorithm would attempt to generate more than 26 bytes of output (including the terminating null).

The tm structure is defined in the <time.h> header. The asctime(), ctime(), gmtime(), and localtime() functions shall return values in one of two static objects: a broken-down time structure and an array of type char. Execution of any of the functions may overwrite the information returned in either of these objects by any of the other functions.

The asctime() function need not be thread-safe.

The asctime_r() function shall convert the broken-down time in the structure pointed to by tm into a string (of the same form as that returned by asctime(), and with the same undefined behavior when input or output is out of range) that is placed in the user-supplied buffer pointed to by buf (which shall contain at least 26 bytes) and then return buf.

Return value

Upon successful completion, asctime() shall return a pointer to the string. If the function is unsuccessful, it shall return NULL.

Upon successful completion, asctime_r() shall return a pointer to a character string containing the date and time. This string is pointed to by the argument buf. If the function is unsuccessful, it shall return NULL.

Errors

No errors are defined.

Tests

Untested

Known bugs

None

See Also

  1. Standard library functions
  2. Table of Contents