Timestamps for measuring time taken in C

UpdatedDecember 31, 2023

I am Jyotiprakash, a deeply driven computer systems engineer, software developer, teacher, and philosopher. With a decade of professional experience, I have contributed to various cutting-edge software products in network security, mobile apps, and healthcare software at renowned companies like Oracle, Yahoo, and Epic. My academic journey has taken me to prestigious institutions such as the University of Wisconsin-Madison and BITS Pilani in India, where I consistently ranked among the top of my class.

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In addition to my professional pursuits, I am passionate about teaching and sharing knowledge. I have spent two years as a teaching assistant at UW Madison, where I taught complex concepts in operating systems, computer graphics, and data structures to both graduate and undergraduate students. Currently, I am an assistant professor at KIIT, Bhubaneswar, where I continue to teach computer science to undergraduate and graduate students. I am also working on writing a few free books on systems programming, as I believe in freely sharing knowledge to empower others.

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Jyotiprakash's Blog

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I'm Jyotiprakash, a software dev and professor at KIIT, with expertise in system programming.

Tracking the amount of time it takes for particular program components to execute involves measuring the performance of a C program by recording time stamps. This is particularly useful for identifying bottlenecks and optimizing performance. Here's a detailed explanation with a real-world example:

Tools for Time Measurement in C

In C, you can use various functions to record time stamps. The most common are:

clock() from time.h - Provides processor time, which is the actual CPU time the process has used, independent of other processes.
gettimeofday() from sys/time.h (mostly on Unix-like systems) - Provides wall clock time, which is the actual real-world time.

Imagine we have a C program that sorts an array. We want to measure how long the sorting algorithm takes.

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

void sort(int array[], int n); // Sorting function prototype

int main() {
    int array[] = { /* Some large number of elements */ };
    int n = sizeof(array) / sizeof(array[0]);

    // Record start time
    clock_t start = clock();

    // Perform sorting
    sort(array, n);

    // Record end time
    clock_t end = clock();

    // Calculate time taken
    double time_taken = ((double)(end - start)) / CLOCKS_PER_SEC; // Convert to seconds

    printf("Sorting took %f seconds to execute \n", time_taken);
    return 0;
}

void sort(int array[], int n) {
    // Sorting logic (e.g., quicksort, bubblesort)
}

Explanation

Include Necessary Headers: time.h for clock() function.
Sorting Function: sort() is a placeholder for any sorting algorithm.
Start Time: Before the sorting starts, we record the time using clock().
Sorting Operation: The array is sorted using the specified algorithm.
End Time: After sorting, we record the time again.
Calculate Duration: The difference between end and start times gives the total CPU time used. It's converted to seconds for readability.
Output: The program prints the time taken to sort the array.

Real-World Application

In real-world applications, such as database management systems or high-frequency trading algorithms, performance is critical. By measuring how long different parts of these systems take to execute, developers can identify and optimize the slowest parts to improve overall performance.

For instance, a trading algorithm might use time stamping to measure the latency between receiving market data and executing a trade. Identifying and reducing this latency can significantly impact the algorithm's success.

Caveats

Granularity: clock() may not have fine-grained resolution for very fast operations. In such cases, hardware-specific timers or higher-resolution timers (like clock_gettime() on some systems) might be necessary.
CPU Time vs. Wall Time: clock() measures CPU time, which is different from wall time (gettimeofday()). For I/O-bound operations, wall time is more relevant.
System Differences: Time measurement functions may behave differently on different operating systems. For cross-platform consistency, consider using libraries like boost::chrono.

This approach to performance measurement is crucial in optimization and is widely used in systems programming, game development, and scientific computing.

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