How can I create C header files

Question

I want to be able to create a collection of functions in a header file that I could  include in one of my C Programs

User · Answer

Header files can contain any valid C code, since they are injected into the compilation unit by the pre-processor prior to compilation.

If a header file contains a function, and is included by multiple .c files, each .c file will get a copy of that function and create a symbol for it. The linker will complain about the duplicate symbols.

It is technically possible to create static functions in a header file for inclusion in multiple .c files. Though this is generally not done because it breaks from the convention that code is found in .c files and declarations are found in .h files.

See the discussions in C/C++: Static function in header file, what does it mean? for more explanation.

User · Answer

Open your favorite text editor Create a new file named whatever h Put your function prototypes in it   DONE   Example whatever h   ifndef WHATEVER H INCLUDED  define WHATEVER H INCLUDED int f int a    endif   Note  include guards  preprocessor commands  added thanks to luke  They avoid including the same header file twice in the same compilation  Another possibility  also mentioned on the comments  is to add  pragma once but it is not guaranteed to be supported on every compiler   Example whatever c   include  whatever h   int f int a    return a   1      And then you can include  whatever h  into any other  c file  and link it with whatever c s object file   Like this   sample c   include  whatever h   int main int argc  char   argv        printf   d n   f 2       prints 3        return 0      To compile it  if you use GCC      gcc -c whatever c -o whatever o   gcc -c sample c -o sample o   To link the files to create an executable file     gcc sample o whatever o -o sample   You can test sample       sample 3

[c] How can I create C header files

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