strftime() function in C/C++

Last Updated : 8 Aug, 2026

The strftime() function in C is used to format date and time values according to specified formatting rules. It is defined in the <time.h> header file and uses the struct tm structure to represent the date and time components. 

  • Converts a struct tm time value into a formatted charact er string.
  • Supports format specifiers such as %d, %m, %Y, %H, %M, and %a to customize the output format.
C 
#include <stdlib.h>
#include <stdio.h>
#include <time.h> 
#define Size 50

int main ()
{
    time_t t ;
    struct tm *tmp ;
    char MY_TIME[Size];
    time( &t );
    
    //localtime() uses the time pointed by t ,
    // to fill a tm structure with the 
    // values that represent the 
    // corresponding local time.
    
    tmp = localtime( &t );
    
    // using strftime to display time
    strftime(MY_TIME, sizeof(MY_TIME), "%x - %I:%M%p", tmp);
    
    printf("Formatted date & time : %s\n", MY_TIME );
    return(0);
}

Formatted date & time : 03/20/17 - 02:55PM

Syntax

size_t strftime(char *s, size_t max, const char *format, const struct tm *tm);

1. Parameters

Explain the four parameters clearly:

  • s: Character array where the formatted date and time is stored.
  • max: Maximum number of characters that can be written to s.
  • format: Format string containing specifiers such as %d, %m, %Y, etc.
  • tm: Pointer to the struct tm containing the date and time information.

2. Return Value

This is important for strftime().

  • Returns the number of characters written to the destination array, excluding the terminating null character.
  • Returns 0 if the formatted result cannot fit within the specified maximum size.

strftime() function formats the broken-down time tm according to the formatting rules specified in format and store it in character array s.

Some format specifiers for strftime() are shown as follows: 

%x = Preferred date representation 
%I = Hour as a decimal number (12-hour clock). 
%M = Minutes in decimal ranging from 00 to 59. 
%p = Either "AM" or "PM" according to the given time value, etc. 
%a = Abbreviated weekday name 

%^a = Abbreviated weekday name in capital letters
%A = Full weekday name 
%b = Abbreviated month name 

%^b = Abbreviated month name in capital letters
%B = Full month name March 
%c = Date and time representation 
%d = Day of the month (01-31) 
%H = Hour in 24h format (00-23) 
%I = Hour in 12h format (01-12) 
%j = Day of the year (001-366) 
%m = Month as a decimal number (01-12) 
%M = Minute (00-59)

Structure struct tm is defined in time.h as follows:  

struct tm 
{
   int tm_sec;         // seconds
   int tm_min;         // minutes
   int tm_hour;        // hours
   int tm_mday;        // day of the month
   int tm_mon;         // month
   int tm_year;        // The number of years since 1900
   int tm_wday;        // day of the week
   int tm_yday;        // day in the year
   int tm_isdst;       // daylight saving time    
};

Advantages of strftime()

The function provides a flexible way to convert date and time information into human-readable strings.

  • Supports multiple predefined format specifiers for customizing date and time output.
  • Helps generate consistent date and time formats for display, logging, and reports.

Limitations of strftime()

Although strftime() is flexible, it has some limitations when formatting date and time values.

  • The output depends on the specified format and the locale settings of the system.
  • If the destination buffer is too small, the function returns 0 and the formatted result may not be stored completely.
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