Standard library header <ctime> - cppreference.com

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# Standard library header <ctime>

From cppreference.com
< cpp‎ | header

This header was originally in the C standard library as `<time.h>`.

This header is part of the C-style date and time library.

### [edit] Macro Constants

CLOCKS_PER_SEC | number of processor clock ticks per second (macro constant) [edit]
NULL | implementation-defined null pointer constant (macro constant) [edit]

### [edit] Types

clock_t | process running time (typedef) [edit]
size_t | unsigned integer type returned by the `sizeof` operator (typedef) [edit]
time_t | time since epoch type (typedef) [edit]
tm | calendar time type (class) [edit]
timespec (since C++17) | time in seconds and nanoseconds (struct) [edit]

### [edit] Functions

##### Time manipulation
clock | returns raw processor clock time since the program is started (function) [edit]
time | returns the current time of the system as time since epoch (function) [edit]
difftime | computes the difference between times (function) [edit]
timespec_get (since C++17) | returns the calendar time based on a given time base (function) [edit]
##### Format conversions
ctime | converts a `time_t` object to a textual representation (function) [edit]
asctime | converts a `tm` object to a textual representation (function) [edit]
strftime | converts a `tm` object to custom textual representation (function) [edit]
wcsftime | converts a tm object to custom wide string textual representation (function) [edit]
gmtime | converts time since epoch to calendar time expressed as Universal Coordinated Time (function) [edit]
localtime | converts time since epoch to calendar time expressed as local time (function) [edit]
mktime | converts calendar time to time since epoch (function) [edit]

### [edit] Synopsys

    #define NULL /* see definition */
    #define CLOCKS_PER_SEC /* see definition */
    #define TIME_UTC /* see definition */
    namespace std {
      using size_t = /* see definition */;
      using clock_t = /* see definition */;
      using time_t = /* see definition */;
      struct timespec;
      struct tm;
      clock_t clock();
      double difftime(time_t time1, time_t time0);
      time_t mktime(struct tm* timeptr);
      time_t time(time_t* timer);
      int timespec_get(timespec* ts, int base);
      char* asctime(const struct tm* timeptr);
      char* ctime(const time_t* timer);
      struct tm* gmtime(const time_t* timer);
      struct tm* localtime(const time_t* timer);
      size_t strftime(char* s, size_t maxsize, const char* format, const struct tm* timeptr);
    }

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