cpp command in Linux with Examples (original) (raw)

Last Updated : 15 May, 2019

cpp is the C language preprocessor, it is automatically used by your C compiler to transform your program before compilation. It is also termed as a macro processor because it is used to give abbreviations for the longer piece of code. It can only be used with C, C++ and Objective-C source code. Using with other programming languages may cause uncertain problems.Syntax:

cpp [-options] infile outfile

Some Important Options:

• -D name : Predefine name as a macro.
• -D name=definition : The contents of definition are tokenized and processed as if they are written in program itself.
• -U name : Cancel any previous definition of macro.
• -undef : Do not predefine any system-specific or GCC-specific macros. The standard predefined macros remain defined.
• -I dir : Add the directory dir to the list of directories to be searched for header files.
• -Wall : Turns on all optional warnings which are desirable for normal code.
• -Wcomments : Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a backslash-newline appears in a // comment.
• -Wendif-labels : Warn whenever an #else or an #endif are followed by text.
• -w : Suppress all warnings, including those which GNU CPP issues by default.
• -M : Instead of outputting the result of preprocessing, output a rule suitable for make describing the dependencies of the main source file.
• -MM : Like -M but do not mention header files that are found in system header directories.
• -x c
• -x c++
• -x objective-c
• -x assembler-with-cpp : All four above Specify the source language: C, C++, Objective-C, or assembly. This has nothing to do with standards conformance or extensions; it merely selects which base syntax to expect.

Examples: We have created two codes to explain the concept we will refer them as code_a.c and code_b.c.

#include void main() { printf("Hello, World!"); }

code_a.c

#include void main() { printf(out); }

code_b.c