c++ – How a main function is being called in a c/cpp project – Education Career Blog

Good day good-looking computer people,

I might be asking a bit too much, but here it goes.

I’m trying to do a bit of reserve engineering on this sound library. Looking at the main.cpp file (which I have posted below) it has two methods, setup and play. I’m a bit confused as to how this is working:

1. When you run the Xcode project, shouldn’t there be a main function that is the first method called? I don’t see that here.

2. The play function is being called (because I hear music), but it must be from elsewhere since in needs the argument output. Where could it be being called from?

To try to be a bit more specific, this is my question:

1. If the program isn’t starting from a main method in the main.cpp file, where else could it be starting from ?

#include "maximilian.h"

double outputs2,moreoutputs2; //some track outputs
double filtered, ramped, filtered2; 
osc buffertest,ramp;
mix mymix,bobbins;//some panning busses
double env4={200,0,0,50};//the kick drum pitch envelope data
double env26={10000,0,9000,5,0,5};//the hi hat pitch envelope dat
envelope b,f;//two envelopers
sample beats;


extern int channels=2;//stereo-must be supported by hardware
extern int buffersize=256;//should be fine for most things
extern int samplerate=44100;//SR must be supported by card. It's always the default

void setup() {//some inits
    b.amplitude=env0;//starting value for envelope b
    f.amplitude=env20;//same for f
    beats.load("/Users/ericbrotto/Desktop/beats.wav");//put a path to a soundfile here.           Wav format only.
    printf("Summary:\n%s", beats.getSummary());//get info on samples if you like
 }

 void play(double *output) {//this is where the magic happens. Very slow magic.
    filtered2=beats.play(1*(1./34), 0, beats.length()); 
    bobbins.stereo(filtered2, moreoutputs, 0.5);//invert the pan
    output0=outputs0+moreoutputs0;//stick it in the out!!
    output1=outputs1+moreoutputs1;
 }

Thanks!

If the program isn’t starting from a
main method in the main.cpp file,
where else could it be starting from ?

From a main method in a different source file or pre-compiled library, probably, or definitely.

A main method is required and must have the name main unless you tell the compiler otherwise. It is possible that the main method gets included through a header or is implemented by a macro.

in the directory where you unpacked the library –

find . | xargs egrep "main"

It has to be there somewhere… 😉

1. You’re dealing with a library, not a standalone program. It doesn’t have a main function, since it won’t run on its own. When a developer uses a library, such as this, his application calls out to the library’s functions (such as play).

2. I don’t entirely understand from what you hear music. What have you compiled? An example program? In that case, that example program probably does have a main function and at some point calls the library’s play.

main is either getting defined in the the maximillian.h, something it includes, or it is already compiled into the maximillian library.

Put a breakpoints on the front of each function, run the app, and examine call stack when breakpoint is hit.

what i understand from it is the cpp file for the implementation of this library’s header it is not a complete program but when you use this lib in your program you have to do is

1) use its setup method to setup or load the file u want to play

2) you have to call play to play the sound

that it about this/.

For your question

If the program isn’t starting from a main method in the main.cpp file,
where else could it be starting from
?

Global objects and static members of classes will be initialized before call to main() function.

For below code

class Test
{
public:

};

Test* fun()
{
    return new Test;
}

Test *p = fun();

int main()
{
}

For initializing pointer p, fun() will be called before main() function.

Line 491 of maximillian.cpp