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Scoping rules of function declarations and repeated declarations....

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• Scoping rules for function declarations

  • Recall: Structure of a C program:

    .... funcDef1(....) { ... } .... funcDef2(....) { ... } ....

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  • Places where you can place a function declaration:

    .... <---- Here funcDef1(....) { <---- Here ... } .... <---- Here funcDef2(....) { <---- Here ... } .... <---- Here

    The scope (= validity) of the function declaration depends on where you place the function declaration

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  • Rule 1: placing a declaration outside functions:

    A declaration placed outside a function is valid everywhere following the declaration

    Example:

    .... funcDef1(....) { ... square() is NOT declared here } .... double square( double x ) ; // Declare "square()" funcDef2(....) { ... square() is declared here } ....

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  • Rule 2:

    A declaration placed inside a function is only valid (= recognized) within the function scope

    Example:

    int f( ... ) { double square( double x); // declare square() function ... // square() is declared here } int g( ... ) { // square() is not declared here !!! }

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• Repeating a declaration: Multiple declaration of the same function
  • Fact:

    You can (= allowed) have multiple declarations As long as the different declaration do not conflict !!!

    Example:

    extern double square ( double ); extern double square ( double ); // Repeat is OK... int main( int argc, char *argv[] ) { double a, b; a = 4.0; b = square( a ); // Call square printf("Square of %lf = %lf\n", a, b); }