Pragmas are all about hints!

PublishedDecember 24, 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.

At my core, I am a computer enthusiast with a profound interest in understanding the intricacies of computer programming. My skills are not limited to application programming in Java; I have also delved deeply into computer hardware, learning about various architectures, low-level assembly programming, Linux kernel implementation, and writing device drivers. The contributions of Linus Torvalds, Ken Thompson, and Dennis Ritchie—who revolutionized the computer industry—inspire me. I believe that real contributions to computer science are made by mastering all levels of abstraction and understanding systems inside out.

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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C Programming

Part 27 of 50

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Jyotiprakash's Blog

253 posts

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

The #pragma directive in C is used to provide additional information to the compiler. It's compiler-specific and can be used for various purposes, such as controlling compiler warnings, optimizing code, or specifying architecture-specific features. Here's an example that uses #pragma to disable a specific compiler warning:

Example: Using `#pragma` to Disable a Warning

// main.c

#include <stdio.h>

void foo() {
    int x;
    // Some code that may trigger a specific warning
}

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-function"

void unusedFunction() {
    // This function is intentionally left unused to trigger a warning
}

#pragma GCC diagnostic pop

int main() {
    printf("Hello, World!\n");
    return 0;
}

In this example, the foo function contains some code that might trigger a warning. To avoid displaying this warning, we use #pragma GCC diagnostic push before the code and #pragma GCC diagnostic ignored "-Wunused-function" to disable the specific warning. After the code, we use #pragma GCC diagnostic pop to revert to the previous warning settings.

Now, let's create a bash script (compile_and_run.sh) to compile the code:

#!/bin/bash

# Compile the C code
gcc -Wall main.c -o my_program

# Run the compiled program
./my_program

Explanation:

-Wall: Enables most warning messages during compilation.
#pragma GCC diagnostic push: Saves the current diagnostic state.
#pragma GCC diagnostic ignored "-Wunused-function": Temporarily disables the warning for unused functions.
#pragma GCC diagnostic pop: Restores the previous diagnostic state.

When you run the bash script, it will compile the code, and you'll observe that the warning for the unused function is suppressed:

Hello, World!

Keep in mind that the use of #pragma directives is compiler-specific, and the above example is specifically for GCC. Other compilers may have different directives and options. Always refer to the documentation of your compiler for accurate and detailed information on #pragma usage.

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C Programming

Where do your variables live?

More from this blog

Example: Using #pragma to Disable a Warning

Example: Using `#pragma` to Disable a Warning