Thread: Inline Definitions and Declarations?

  1. #1
    Student legit's Avatar
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    Inline Definitions and Declarations?

    Hey programmers of C Board
    I have a question about inline functions. If I declare a function inline, do I have to define it as inline also? I'll demonstrate:

    SomeHeader.h
    Code:
    class Someclass
    {
    public:
        inline void vSomeFunc();
    };
    ...and in my .cpp file I have:

    SomeCppFile.cpp
    Code:
    inline void SomeClass::vSomeFunc()
    {
        std::cout << "Some output" << std::endl;
    }
    ... so in my source file, do I need to define the function vSomeFunc as inline if I have already declared it as inline?

  2. #2
    Cat without Hat CornedBee's Avatar
    Join Date
    Apr 2003
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    8,895
    1) The compiler needs to see the definition of an inline function. You need to put the implementation into the header file.

    2) Once a function is declared inline once, it sticks. Redeclarations won't change that. Declare a function first non-inline and then inline, however, and it becomes inline. Define a function non-inline, and then declare it inline, and the program is ill-formed, as per Core Issue 317.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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