raise() Function Example in C Programming

In this source code example, we will see how to use the raise() function in C programming with an example.

raise() Function Overview

The raise() function in C is used to send a signal to the current process or thread. This can be useful to test how your program responds to specific signals, simulate signal-based interruptions, or invoke signal handlers explicitly. The raise() function is located in the <signal.h> header. 

Key Points: 

- Requires the <signal.h> header. 

- It can be used to generate signals programmatically. 

- Typically used with custom signal handlers or to test signal handling routines. 

- The return value is 0 if successful, and non-zero if an error occurs.

Source Code Example

#include <stdio.h>
#include <signal.h>  // Required for raise(), signal(), and signal definitions

// Custom handler for SIGUSR1 signal
void handle_sigusr1(int sig_num) {
    printf("Caught the SIGUSR1 signal (%d). Handling it...\n", sig_num);
}

int main() {
    // Set our handler for SIGUSR1
    signal(SIGUSR1, handle_sigusr1);

    printf("Before raising the signal...\n");

    // Generate the SIGUSR1 signal for this process
    raise(SIGUSR1);

    printf("After raising the signal...\n");

    return 0;
}

Output

Before raising the signal...
Caught the SIGUSR1 signal (10). Handling it...
After raising the signal...

Explanation

1. The necessary headers are included: stdio.h for I/O operations and signal.h for the raise(), signal() function, and signal definitions.

2. We define the handle_sigusr1 function, a custom handler for the SIGUSR1 signal. This handler merely prints a message indicating the signal was caught.

3. In the main() function, we set our custom handler for the SIGUSR1 signal using signal(SIGUSR1, handle_sigusr1).

4. We then print a message to indicate we're about to generate the SIGUSR1 signal.

5. Using the raise() function, we generate the SIGUSR1 signal for the current process. This results in our custom handler being invoked.

6. Once the signal has been handled, the program resumes its regular flow and prints another message.

The raise() function in C provides a means to generate signals programmatically, allowing developers to have fine-grained control over the signal behavior of their applications. 

The raise() function can be very useful in scenarios where you want to test how your program handles specific signals, especially when combined with custom signal handlers.