27 Time library [time]

27.14 Header <ctime> synopsis [ctime.syn]

#define NULL see [support.types.nullptr]
#define CLOCKS_PER_SEC see below
#define TIME_UTC see below

namespace std {
  using size_t = see [support.types.layout];
  using clock_t = see below;
  using time_t = see below;

  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);
The contents of the header <ctime> are the same as the C standard library header <time.h>.255
The functions asctime, ctime, gmtime, and localtime are not required to avoid data races ([res.on.data.races]).
See also: ISO C 7.27
strftime supports the C conversion specifiers C, D, e, F, g, G, h, r, R, t, T, u, V, and z, and the modifiers E and O.