Preprocessors in C programming language

The C preprocessor is a micro processor that is used by compiler to transform your code before compilation.All preprocessor commands begin with a hash symbol (#).


Some of the common C preprocessor directive are :

Directives Description
#include Inserts a particular header from another file.
#define Substitutes a preprocessor macro.
#undef Undefines a preprocessor macro.
#ifdef Returns true if this macro is defined.
#ifndef Returns true if this macro is not defined.
#if Tests if a compile time condition is true.
#else The alternative for #if.
#elif #else and #if in one statement.
#endif Ends preprocessor conditional.
#error Prints error message on stderr.
#pragma Issues special commands to the compiler, using a standardized method.

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