The C date and time functions are a group of functions in the standard library of the C programming language implementing date and time manipulation operations.[1] They provide support for time acquisition, conversion between date formats, and formatted output to strings.
History
The format string used in strftime traces back to at least PWB/UNIX 1.0, released in 1977. Its date system command includes various formatting options.[2][3] In 1989, the ANSI C standard is released including strftime and other date and time functions.[4]
Overview of functions
The C date and time operations are defined in the time.hheader file (ctime header in C++).
returns the current time of the system as a time_t value, number of seconds, (which is usually time since an epoch, typically the Unix epoch). The value of the epoch is operating system dependent; 1900 and 1970 are often used. See RFC 868.
The timespec and related types were originally proposed by Markus Kuhn to provide a variety of time bases, but only TIME_UTC was accepted.[6] The functionalities were, however, added to C++ in 2020 in std::chrono.
#include<time.h>#include<stdlib.h>#include<stdio.h>intmain(void){time_tcurrent_time;char*c_time_string;/* Obtain current time. */current_time=time(NULL);if(current_time==((time_t)-1)){(void)fprintf(stderr,"Failure to obtain the current time.\n");exit(EXIT_FAILURE);}/* Convert to local time format. */c_time_string=ctime(¤t_time);if(c_time_string==NULL){(void)fprintf(stderr,"Failure to convert the current time.\n");exit(EXIT_FAILURE);}/* Print to stdout. ctime() has already added a terminating newline character. */(void)printf("Current time is %s",c_time_string);exit(EXIT_SUCCESS);}