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 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 
#include 
#include  
#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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