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Why does each .h file starts with #ifndef #define #endif? We can certainly compile the program without those directives.
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A header file is a file with extension . h which contains C function declarations and macro definitions to be shared between several source files. There are two types of header files: the files that the programmer writes and the files that comes with your compiler.
Things like class declarations, function prototypes, and enumerations typically go in header files.
A file saved with h file extension is a header file used in C/C++ files to include the declaration of variables, constants, and functions. These are referred by the C++ implementation files that contain the actual implementation of these functions.
The primary purpose of a header file is to propagate declarations to code files. Header files allow us to put declarations in one location and then import them wherever we need them.
It's a so-called "include guard". The purpose is to prevent the file from having to be parsed multiple times if it is included multiple times.
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It prevents multiple inclusions of a single file. The same can be done using
#pragma once
directive, but those #ifndefs are standard thus supported by every compiler.
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