inclusion of header files

i have a file named functions.h....now i know that it is not wise to define functions in the header files but that is least of my concern as compared to the problem which cropped up...

i defined a function in a functions.h named

 void sayhi()
{
  cout<<"hi";
}

now i made a lines.h file whose functions were defined in lines.cpp file...in lines.cpp file i included functions.h...and used sayhi(); in the constructor of lines class...then in mymain.cpp(containing int main) 开发者_如何转开发i again included functions.h and in the main i called sayhi();

but when i compiled the program it showed an error in mymain.cpp telling that sayhi() has already been defined in lines.obj...can u point out what am i doing wrong??

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Well, the solution is to declare the function in functions.h and then define it in functions.cpp, the way nature intended.

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Making your function inline avoids this multiple definition problem.

Try,

inline void sayhi()
{
  cout<<"hi";
}

This link might be helpful to you.

In particular, it references section 7.1.2 of the ISO C++ standard:

An inline function shall be defined in every translation unit in which it is used and shall have exactly the same definition in every case (3.2).

which is why the one-definition-rule is circumvented.