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The simplest way to compile a C program that consists of multiple program files

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• The simplest (amateur) way to compile a multi-file C program
  • Example of a multi-file C program:

    File 1 (prog1.c)	File 2 (prog2.c)
    float f(float x); // Declare function f( ) int main( int argc, char *argv[] ) { int a, b; float c, d; a = 2; b = f( a ); // Call f( ) printf( "f(%d) = %d\n", a, b); c = 2.0; d = f( c ); // Call f( ) printf( "f(%f) = %f\n", c, d); }	float f( float x ) { return ( x*x ); }

    The simplest way to compile a multi-file C program:

    gcc prog1.c prog2.c ....

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  • Example: demo

    cd /home/cs255000/demo/c/multiple-files gcc prog1.c prog2.c a.out Output: f(2) = 4 f(2.000000) = 4.000000

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• How the C compiler processes multi-file C programs
  • Compiling a multi-file C program:

    The C compiler compiles (= translates) one C program file at a time Each C program is compiled (= translated) independently : The information gathered in the translation process of a C program file is discarded at the end of the C program file !!!

    Schematically:

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• What's wrong with the simplest way to compile multi-file C program
  • Problem:

    The command: gcc prog1.c prog2.c .... will: (Re-)compile all the source code in program files prog1.c, prog2.c, .... Even if the source code has not changed !!!!

    Result:

    If there are many C program files, it will take a long time to recompile !!!! (When I was a graduate student, I saw a couple of students working on their MS thesis using the naive compilation.... every time they compile their project, they take a 1 hr coffee break !!!)