The clock() function

The ISO C standard specifies that

The clock function determines the processor time used.

It is clear that the result should be processor time instead of wall-clock time (real time).

It turns out that clock() in Microsoft C does return the wall-clock time instead of processor time.

I do understand Microsoft probably were not intentionally trying to violate the standard. It is meaningless to talk about processor time in DOS (nor does DOS provide any mechanism to measure processor time, afaik), and many programs used clock() to measure real time even if there were lots of system calls, disk accesses, etc. (which would make processor time significantly differ from real time in time-sharing systems). Probably Microsoft intended to maintain this “compatibility.” But is this really necessary? They could have corrected this either during the migration from single-task DOS to time-sharing Windows, or from 16-bit Windows 3 to 32-bit Windows 95/NT – just one more “incompatibility,” compared to other huge differences, not so important, was it?

Tags: C/C++, DOS, time, Windows