cpp Command in Linux

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cpp command in Linux is a C language processor that is automatically used by your C compiler to transform your source code into a form suitable for compilation. You can use the cpp command with C, C++ and Object-C source codes. It performs tasks like file inclusion, macro expansion, and conditional compilation, and helps you make your code more manageable for the compiler.

Table of Contents

Here is a comprehensive tutorial to understand the various options available with the cpp command −

• Syntax of cpp Command
• cpp Command Options
• How to Use cpp Command in Linux ?

Syntax of cpp Command

When invoking cpp, you typically do so from the command line or within a build system. Here’s the basic syntax to use the cpp command on Linux system −

cpp [options] input_file output_file

Where, input_file is the name of the source code file that you want to preprocess (usually a C, C++, or Objective-C file). The output_file is the name of the output file where the preprocessed code will be written. While [options] are different flags that can be used with the cpp command to customize the command’s behavior.

Note − The common preprocessor directives are −

• #include − Includes a header file.
• #define − Defines a macro.
• #ifdef, #ifndef, #else, #endif − Conditional compilation directives.

cpp Command Options

How to Use cpp Command in Linux?

To use cpp command on Linux to preprocess the code, first you are required to create a file with the .c extension. Though it can also handle .cpp for C++ and .m for Objective-C. The file must contain your source code, which will be processed by cpp command.

Let’s create a file named code.c on Linux by using the nano editor −

nano code.c

Inside the code.c file, add you desired code, as an example, we are using the following code −

#include <stdio.h>

#define PI 3.14159

int main() {
   printf("The value of PI is: %f\n", PI);
   return 0;
}

Save your code.c file using CTRL+X, add Y and press Enter, then run the code using the GCC compiler through the following command −

gcc code.c -o PI_code

You can replace input file name code.c and output file name PI_code according to your needs.

Note − If gcc is not installed , you can install it from your default system’s package manager.

After the code is executed, you to run the output file to print the result on the terminal −

./PI_code

Once everything is done, you can simply use the cpp command to preprocess the code and save the resulting output to preprocessed.c.

cpp code.c > preprocessed.c

This will create a file named preprocessed.c containing the code after preprocessing. You can open this file using nano editor or cat command to see the result.

You can also view the preprocessed output on standard output by using the -E option with the cpp command −

cpp -E code.c

To suppress all warning messages, you can use the -W option with the cpp command, for example −

cpp -W code.c

For exploring more options, you can get help from the cpp manual by opening it on the terminal using the below-given command −

man cpp

Conclusion

The cpp command is an essential tool in the C, C++, and Objective-C development process. It acts as a preprocessor by helping you transform your source code into a format suitable for compilation.

In this tutorial, we have provided the basic syntax of the cpp command along with its different options or flags. We have also discussed cpp command usage with the help of an example. Using this example as a base, you can explore more options with the cpp command to tailor the preprocessing process to your specific needs.