Question

When I begin to learn C++ and algorithms. I want to group code in module paradigm. so I had divide the sort procedure into 3 files, as follows:

sort.h

namespace sort
{
    void insertSort(int* a,int size);    
}

sort.cpp

#include "sort.h"
namespace sort
{
}
void sort::insertSort(int* a,int size)
{
    int i,j,key;
    for(j=1;j<size;j++)
    {
        key=a[j];
        i=j-1;
        while(i>=0 && a[i]>key)
        {
            a[i+1]=a[i];
            i=i-1;
        }
        a[i+1]=key;
    }
}

main.cpp

#include<iostream>
#include"sort.h"
int main()
{
    int a[6]={5,2,4,6,1,3};
    sort::insertSort(a,6);
    for(int i=0;i<6;i++) std::cout<<a[i]<<'\t';
    return 0;
}

When I use Dev-C++ to compile the three files. I got the the below error information:

[Linker Error] undefined reference to `sort::insertSort(int*, int)’

I don’t know why. I think I have include the file “sort.h”, so why is it also telling me that the compile can’t reference to the method sort::insertSort()?

Answer 1

When you’re building the entire program, make sure you’re linking all the object files together. The linker is complaining because your main() function is calling the sort::insertSort function, which has been declared in sort.h, but the definition for which has not been included in the program as a whole.

I don’t know offhand what parameters to your particular Dev-C++ environment are required, but typically, make sure that all the cpp files are in the command line you send to the compiler frontend.