Tell them if you cannot compile! #error

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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Jyotiprakash's Blog

253 posts

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

The #error directive in C is used to generate a compilation error with a custom error message. This can help enforce certain conditions during compilation. Let's go through a detailed example that includes the use of #error, bash scripting, and environment variables.

Example: Using #error with Bash and Environment Variables

// main.c

#include <stdio.h>

// Uncomment the following line to enable a feature
#define ENABLE_FEATURE

#ifdef ENABLE_FEATURE
    // Perform feature-specific configuration
#else
    // Generate a compilation error if the feature is not enabled
    #error "Feature is not enabled. Please define ENABLE_FEATURE."
#endif

int main() {
    printf("Program execution after feature configuration.\n");
    return 0;
}

Bash script (compile_and_run.sh):

#!/bin/bash

# Uncomment the following line to enable the feature
# export ENABLE_FEATURE=true

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

In this example, the code includes a feature configuration block that is supposed to be enabled only when the ENABLE_FEATURE macro is defined. If ENABLE_FEATURE is not defined, a compilation error is generated using #error with a custom error message.

Compilation and Execution

Initially, try to compile without defining ENABLE_FEATURE:

 chmod +x compile_and_run.sh
 ./compile_and_run.sh

This will result in a compilation error with the specified message:

 main.c:12:2: error: #error "Feature is not enabled. Please define ENABLE_FEATURE."
  #error "Feature is not enabled. Please define ENABLE_FEATURE."
   ^~~~~

Uncomment the line # export ENABLE_FEATURE=true in the bash script and then try to compile again:
```
 ./compile_and_run.sh
```
Now, the compilation should succeed, and the program can be executed:
```
 Program execution after feature configuration.
```

This example demonstrates how #error can be used to enforce certain conditions during compilation, and how it can be integrated with bash scripting and environment variables to control the compilation process based on predefined conditions.