C clock() Function

The clock() function in C is a standard library function that returns the processor time consumed by the program. It is part of the C standard library (time.h). This function is useful for measuring the performance of a program or specific parts of a program.

Table of Contents

1. Introduction
2. clock() Function Syntax
3. Examples
   • Measuring Execution Time of a Code Block
   • Using clock() with User Input
4. Real-World Use Case
5. Conclusion

Introduction

The clock() function returns the number of clock ticks elapsed since the program was launched. This can be used to calculate the processor time consumed by the program. The constant CLOCKS_PER_SEC can be used to convert clock ticks to seconds.

clock() Function Syntax

The syntax for the clock() function is as follows:

#include <time.h>
clock_t clock(void);

Returns:

• The function returns the number of clock ticks since the program started. If the processor time is not available or its value cannot be represented, the function returns -1.

Examples

Measuring Execution Time of a Code Block

To demonstrate how to use clock() to measure the execution time of a code block, we will write a simple program that calculates the time taken to execute a loop.

Example

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

int main() {
    clock_t start, end;
    double cpu_time_used;
    int i;

    // Start the clock
    start = clock();

    // Code block to measure
    for (i = 0; i < 1000000; i++);

    // End the clock
    end = clock();

    // Calculate the time taken
    cpu_time_used = ((double) (end - start)) / CLOCKS_PER_SEC;

    // Print the result
    printf("Time taken to execute the loop: %f seconds\n", cpu_time_used);

    return 0;
}

Output:

Time taken to execute the loop: 0.010000 seconds

Using clock() with User Input

This example shows how to use clock() to measure the time taken by the user to enter a string.

Example

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

int main() {
    clock_t start, end;
    double cpu_time_used;
    char input[100];

    // Start the clock
    start = clock();

    // Get user input
    printf("Enter a string: ");
    fgets(input, sizeof(input), stdin);

    // End the clock
    end = clock();

    // Calculate the time taken
    cpu_time_used = ((double) (end - start)) / CLOCKS_PER_SEC;

    // Print the result
    printf("Time taken to enter the string: %f seconds\n", cpu_time_used);

    return 0;
}

Output (example user input time of 3 seconds):

Enter a string: Hello World
Time taken to enter the string: 3.000000 seconds

Real-World Use Case

Profiling Program Performance

In real-world applications, the clock() function can be used to profile the performance of a program, identifying bottlenecks and optimizing code execution.

Example: Profiling a Function

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

// Function to profile
void perform_task() {
    for (int i = 0; i < 1000000; i++);
}

int main() {
    clock_t start, end;
    double cpu_time_used;

    // Start the clock
    start = clock();

    // Call the function to profile
    perform_task();

    // End the clock
    end = clock();

    // Calculate the time taken
    cpu_time_used = ((double) (end - start)) / CLOCKS_PER_SEC;

    // Print the result
    printf("Time taken to execute perform_task(): %f seconds\n", cpu_time_used);

    return 0;
}

Output:

Time taken to execute perform_task(): 0.010000 seconds

Conclusion

The clock() function is essential for measuring the processor time consumed by a program in C. It is useful in various applications, particularly in performance profiling and optimization, where it is necessary to measure and improve the execution time of code blocks or functions.