How to get Epoch/UNIX timestamps in C

In C, getting Epoch timestamps is straightforward, and there are several methods to accomplish this task. This article explores different ways to get Epoch timestamps in C and provides practical use cases.

Using the time.h Library

The C library time.h provides functions for working with time, and the time() function is used to fetch the current Epoch timestamp. This function returns the timestamp as a value of type time_t.

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

int main() {
    time_t epoch_time;
    epoch_time = time(NULL);
    printf("Current Epoch timestamp: %ld\n", (long)epoch_time);
    return 0;
}

This code snippet utilizes the time.h library to fetch the current Epoch timestamp and then displays it.

Use Case 1: Logging timestamps

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

int main() {
    time_t epoch_time;
    epoch_time = time(NULL);
    
    char data[] = "Sensor data reading...";
    printf("%s - timestamp: %ld\n", data, (long)epoch_time);
    
    return 0;
}

In this example, C code is adapted to log data with timestamps. It obtains the current Epoch timestamp and combines it with sensor data for logging.

Use Case 2: Time Duration Calculation

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

int main() {
    time_t start_time, end_time;
    start_time = time(NULL);
    
    // Perform a task or operation
    
    end_time = time(NULL);
    
    long time_elapsed = (long)(end_time - start_time);
    printf("Time taken: %ld seconds\n", time_elapsed);
    
    return 0;
}

This use case demonstrates how to measure the time taken for a task. It records the start and end times and calculates the time elapsed, displaying the result in seconds.

Using the gettimeofday() Function

The gettimeofday() function is another way to obtain the current time, including microseconds. It returns the current time as a struct timeval object, which can be converted to an Epoch timestamp.

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

int main() {
    struct timeval current_time;
    gettimeofday(¤t_time, NULL);
    
    time_t epoch_time = current_time.tv_sec;
    printf("Current Epoch timestamp: %ld\n", (long)epoch_time);
    
    return 0;
}

This code uses the gettimeofday() function to fetch the current time, and then it extracts the seconds component to obtain the Epoch timestamp.

Use Case 3: Expiry timestamp for Cache

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

int main() {
    struct timeval current_time;
    gettimeofday(¤t_time, NULL);
    
    time_t epoch_time = current_time.tv_sec;
    
    char cache_key[] = "cached_data";
    time_t expiry_time = epoch_time + 600; // 10 minutes from now
    
    printf("Cached data that expires at %ld\n", (long)expiry_time);
    
    if (epoch_time > expiry_time) {
        printf("Cache expired. Recaching data...\n");
        // Re-cache the data
    }
    
    return 0;
}

In this example, C code is adapted to calculate the expiry time for cache data. It sets the cache entry to expire in 10 minutes from the current time and checks if the cache has expired.

Use Case 4: Event Scheduling

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

int main() {
    struct timeval current_time;
    gettimeofday(¤t_time, NULL);
    
    time_t epoch_time = current_time.tv_sec;
    time_t event_time = epoch_time + 3600; // 1 hour from now
    
    while (1) {
        gettimeofday(¤t_time, NULL);
        time_t current_epoch_time = current_time.tv_sec;
        
        if (current_epoch_time >= event_time) {
            printf("Event occurred!\n");
            break;
        } else {
            sleep(60); // Check every minute
        }
    }
    
    return 0;
}

This use case demonstrates how to schedule an event to occur in the future. C code adds 3600 seconds (1 hour) to the current time to set the event time and continuously checks for its occurrence.

These code examples illustrate how to get Epoch/UNIX timestamps in C and showcase their applications in practical scenarios. Whether you need to log data with timestamps, calculate time durations, set cache expiry times, or schedule events, Epoch timestamps are versatile tools in C for precise time-related operations.