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Removing the implicit function declaration problem in C

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• Solving the missing function prototype information in C
  • Recall the previous example where the function information was not available when the C compiler needs to translate a function call:

    int main( int argc, char *argv[] ) { float a, b; a = 2; b = f( a ); // The C compiler has NOT seen the definition of float f(float x) // 1. Input conversion ???: float a --> ??? // 2. Output conversion ???: ??? --> float printf("b = %f\n", b); } float f( float x ) // This definition is too late !! { float r; // Define a local variable printf("Input parameter = %f\n", x); r = x * x; // Statement return ( r ); // Return statement }

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  • We can use a

    Function declaration

    to provide the function prototpe information:

    float f( float x ); // Function prototype (function declaration) int main( int argc, char *argv[] ) { float a, b; a = 2; b = f( a ); // The C compiler knows that: float f(float x) // 1. Input conversion: no conversion necessary // 2. Output conversion: no conversion necessaty printf("b = %f\n", b); } float f( float x ) // This definition is too late !! { float r; // Define a local variable printf("Input parameter = %f\n", x); r = x * x; // Statement return ( r ); // Return statement }

    Experiment 2B:

    Program: /home/cs255000/demo/c/set1/experiment2b.c cs255 (1744)> a.out Input parameter = 2.000000 b = 4.000000