# 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 one million, 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

- 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)

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