# CLOCKS_PER_SEC

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< c‎ | chrono

Defined in header ``<time.h>`` |  |
#define CLOCKS_PER_SEC /* implementation-defined */ |  |

Expands to an expression (not necessarily a compile-time constant) of type clock_t equal to the number of clock ticks per second, as returned by clock().

### Notes

POSIX defines `CLOCKS_PER_SEC` as 1'000'000, regardless of the actual precision of clock.

Until standardized as CLOCKS_PER_SEC in C89, this macro was sometimes known by its IEEE std 1003.1-1988 name CLK_TCK: that name was not included in C89 and was removed from POSIX itself in 1996 over ambiguity with _SC_CLK_TCK, which gives number of clocks per second for the function `times`).

### References

- C23 standard (ISO/IEC 9899:2024):

  - 7.27.1/2 Components of time (p: TBD)

- C17 standard (ISO/IEC 9899:2018):

  - 7.27.1/2 Components of time (p: 284)

- C11 standard (ISO/IEC 9899:2011):

  - 7.27.1/2 Components of time (p: 388)

- C99 standard (ISO/IEC 9899:1999):

  - 7.23.1/2 Components of time (p: 338)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 4.12.1 Components of time

### See also

clock | returns raw processor clock time since the program is started (function)
clock_t | processor time since era type (typedef)
C++ documentation for CLOCKS_PER_SEC

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