Confused by extern decalration/definition in header files.

This is a discussion on Confused by extern decalration/definition in header files. within the C Programming forums, part of the General Programming Boards category; Hi All, In many open source project, the header file contains lines such as: extern int x; extern char y; ...

  1. #1
    Registered User
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    Post Confused by extern decalration/definition in header files.

    Hi All,
    In many open source project, the header file contains lines such as:
    extern int x;
    extern char y;
    ...

    And this .h file is included by another foo.c file, so x and y may be accessed in foo.c. These lines in .h, look like variable declarations, because extern variable definition conforms the forms:
    extern int x=10;
    or
    int x;
    or
    int x = 10;

    If 'extern int x' is declaration, then perhaps the definition should be somewhere else(in another file)? or 'extern int x;' is understood as an external definition?

    thanks..

    tony

  2. #2
    Captain Crash brewbuck's Avatar
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    The actual definition (without the "extern" keyword) must exist in one, and only one, .c file.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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