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Header files are not compiled directly, Instead, header files are included into other source files via #include . In fact, when you invoke a C/C++ compiler, before the “real” compiler starts, it runs a pre-processor whose job is to handle the special instructions that begin with # .

In C++ programming, it's common practice to separate class interface information into header files. These header files can later be included in programs that use the class. By precompiling these headers, you can reduce the time a program takes to compile.

This question is generally asked in interviews to confuse the candidate and also to test the knowledge of the student in C programming. So, in short, the answer is yes. We can compile C program without header file. But how?

In C++ programming, it's common practice to separate class interface information into header files. These header files can later be included in programs that use the class. By precompiling these headers, you can reduce the time a program takes to compile.

. c files contain the implementation of the code, while . h files exist to provide interfaces that allow a file to access functions, global variables, and macros from other files.

Header files cannot be replaced at runtime, since they are evaluated at the first step of the compilation of the source code to a fixed binary. What you are looking for is the factory pattern. Create a (pure virtual) interface class ICD . This should contain all common data and member functions.

Only source files are passed to the compiler (to preprocess and compile it). Header files aren't passed to the compiler. Instead, they are included from source files.

GCC looks for headers requested with #include " file " first in the directory containing the current file, then in the directories as specified by -iquote options, then in the same places it would have looked for a header requested with angle brackets.