Measure CPU time and wall clock time of a program in C++

Question

std::clock() measures the number of clock ticks within the duration of your program. In the following code, does it calculate the CPU time or wall clock time?

std::clock_t start; double duration;

start = std::clock();

/* Your algorithm here */

duration = ( std::clock() - start ) / (double) CLOCKS_PER_SEC;

In another scenario, with the following code:

std::clock_t start;
double time;
start = std::clock();
time = start  / (double) CLOCKS_PER_SEC;

What will the value of time be?

Answer 1

From the documentation:

std::clock time may advance faster or slower than the wall clock, depending on the execution resources given to the program by the operating system.