Thread: calling a method from another file

I know this is a real dumb question but my mind completely went blank. In sorts.cpp I have three methods - bubbleSort(int[] array, int first, int last), selectionSort(same), quickSort(same). I don't have a default constructor. In my driver program, how would I call a sort method? Is there no way to do this except to create a sorts constructor and then in my driver create a variable sorts mySort then use mySort.bubbleSort(...) ?

Update: I have 3 files - prog6.cpp, sorts.cpp, and sorts.h. sorts.h is:

Code:

#include <stdexcept>

void selectSort(int array[], int first, int last) throw (std::range_error);
void bubbleSort(int array[], int first, int last) throw (std::range_error);
void quickSort(int array[], int first, int last) throw (std::range_error);

prog6.cpp and sorts.cpp include "sorts.h". sorts.cpp is not a class, just those 3 methods listed above. My question is how do I call any one of those 3 methods in sorts.cpp from prog6.cpp? I tried just writing "selectSort(myArray, 0, 20);" in prog6.cpp but I get the error:

Code:

  [Linker error] undefined reference to `selectSort(int*, int, int)' 
  ld returned 1 exit status 
 Makefile.win [Build Error]  [sortz.exe] Error 1

Code:

else if(*argv[typeIndex] == 's')
    {
        cout << "Selection sort:\n";
        selectSort(array, 0, count);
    }

It's all in how you write your source and header files.

Think of a file as a translation unit. When the compiler starts compiling, it will most likely translate one file at a time. And remember that a prototype for a function is just a declaration of the function to be defined later: it lets the compiler know what sort is intended to be in that translation unit.

So if you write a definition for, say sort() apart from anything that used sort() or knew what sort() was, then the sort.cpp file will compile but probably not link.

This is why header files neatly contain declarations of things, so that you can successfully link anything that you would like to use or define across several translation units.

Knowing this, I would write your files like this:

Code:

// sort.hpp
#ifndef SORT_HPP__
#define SORT_HPP__
void bubble( int *ar, int size );
void select( int *ar, int size );
void quick( int *ar, int first, int last );
#endif

// sort.cpp
#include "sort.hpp"

void quick( int *ar, int first, int last )
{
   // implement
}

void select ( int *ar, int size )
{
  // implement
}

void bubble( int *ar, int size )
{
  //implement
}

Did I make sense?

On a technical note, names with double underscores are reserved to the implementation for any use. As such, it would be safer to use a variant of citizen's example, e.g.,

Code:

#ifndef SORT_HPP_
#define SORT_HPP_

Code:

#ifndef SORT_HPP
#define SORT_HPP