INTRODUCTION TO THE PRE PROCESSOR IN C

Introduction to the pre-processor in C

• Introduction to pre-processor 
• Pre-preprocessor 
• Macro substitution 
• File inclusion directives 
• Conditional compilation 

The compilation does not begin with the C Preprocessor; rather, it is an independent procedure. A simple text replacement tool that tells the compiler to do any necessary preparation before compilation is a C preprocessor.

A macro processor called the C preprocessor is automatically used by the C compiler to make certain alterations before compiling your program. Because it can define macros—shorthand for more complicated constructions—the program is termed a macro processor.

There are four independent features available to you in the C preprocessor:

•       The header files are a part of this. You can replace these declaration files in your software.
•       The C preprocessor can replace actual macros in the program with designed macros with the use of macro extensions. Any element of C code can have its definition shortened by a macro.
•        Conditional collection and precise preprocessing instructions enable the program components to be included or excluded based on different scenarios.
•       Line management when you use a program to merge or reorganize source files into an intermediate file that is then compiled, you can use line control to tell the compiler where the source line originally came from.

 

Preprocessor directives

Beginning with the hash symbol (#), all preprocessor commands go here. For readability, preprocessor directives must begin with the first nonblank character in the first column. This is a complete guide to the most important preprocessor commands –

Macro substitution

The name and text that should be changed in a macro are specified by the #define directive. The preprocessor simply replaces the macro's name with the replacement text in the line of code where the macro is created.

Now we will try the C program

File inclusion directives

1. The document contains Directories used to include user-defined header files in C programs.
2. The file-inclusive directory looks for the header file inside the same directory if the path is left blank.
3. The first step in file-inclusive directives is #include.
4. By giving its path, you can add a certain header file to the current scope.
5. Instead of using triangular brackets to include user-defined header files, we employ "Double Quote".
6. It instructs the compiler to incorporate each named file.

Conditional compilation

Conditional Compilation: We can choose not to compile code that does not match specific requirements or to only compile code that does by using conditional compilation directives.

1. #ifdef: This is the simplest type of conditional directive. This type of block is known as a conditional group. The controlled text will appear in the preprocessor output if the macro name is defined. The controlled text will include preprocessing directives inside a conditional. Their implementation is reliant on the conditional's success. You can stack them in layers, but they have to be fully nested. Put simply, '#endif' always matches the nearest '#ifdef' (or '#ifndef') or '#if'. Furthermore, you cannot create and terminate a conditional group in different files.ss

Syntax:

#ifdef MACRO

    controlled text

#endif /* macroname */