Measure Execution Time in C: time(), clock() and gettimeofday()

Measuring Seconds with time()

#include <stdio.h>
#include <time.h>

int main() {
    // Get current time before operation
    time_t start_time = time(NULL);

    // Perform some operation (e.g., a simple loop)
    for (long i = 0; i < 1000000000; ++i);

    // Get current time after operation
    time_t end_time = time(NULL);

    // Compute time difference
    double duration = difftime(end_time, start_time);

    // Print time difference
    printf("Elapsed time: %.2f seconds
", duration);
    return 0;
}

Sample output:

Elapsed time: 3.00 seconds

Measuring Higher Precision with clock()

#include <stdio.h>
#include <time.h>

int main() {
    // Get CPU clock time before operation
    clock_t start_time = clock();

    // Perform some operation (e.g., a simple loop)
    for (long i = 0; i < 1000000000; ++i);

    // Get CPU clock time after operation
    clock_t end_time = clock();

    // Compute time difference
    double duration = (double)(end_time - start_time) / CLOCKS_PER_SEC;

    // Print time difference
    printf("Elapsed time: %.6f seconds
", duration);
    return 0;
}

Sample output:

Elapsed time: 2.500000 seconds

Measuring Microseconds with gettimeofday()

#include <stdio.h>
#include <sys/time.h>

int main() {
    struct timeval start, end;

    // Get current time before operation
    gettimeofday(&start, NULL);

    // Perform some operation (e.g., a simple loop)
    for (long i = 0; i < 1000000000; ++i);

    // Get current time after operation
    gettimeofday(&end, NULL);

    // Compute time difference
    double duration = (end.tv_sec - start.tv_sec) + (end.tv_usec - start.tv_usec) / 1e6;

    // Print time difference
    printf("Elapsed time: %.6f seconds
", duration);
    return 0;
}

Sample output:

Elapsed time: 2.499999 seconds

Key Points

time() : returns seconds as an integer, low precision.

clock() : provides CPU time, higher precision.

gettimeofday() : offers microsecond precision.

Actual timings vary based on system performance and the workload.