my program is copy file to another

Hello,

I did this programu to read and write the close a program when you have 2 files
the problem is how can I edit this program first to copy the whole file and on the same time copy the part of it ..any boday have this code..

Code:

#include <iostream>
#include <fstream>
#include <conio.h>
using namespace std;
#define NAMELEN 20
int main (int argc, char *argv[]) 
{
    char *source, *target; 
   void sequence(char*,int,char*);
    int i;
    int numBytes;
    int seq; 
   
    if (argc != 4)
    {
        cout << "Wrong format\nThe command:\n" << argv[0] << " source target bytes\n";
        exit(1);
    }
    
    if (strlen(argv[1]) >=NAMELEN-1) 
    {
        cout << "Please check file name, it is too long\n";       
        exit(0);
    }
    
    if (strlen(argv[2]) >=NAMELEN-1) 
    {
        cout << "Please check file name, it is too long\n";        
        exit(0);
    }
    source=argv[1];
    target=argv[3];
    
    numBytes=atoi(argv[2]);
    
    
    sequence(source,numBytes,target);
    
     getch();
}
void sequence(char* src,int nbytes,char* tgt)
{
     ifstream inFile ;
     ofstream outFile(tgt, ios::out | ios::binary);
     char *msg; 
    msg=new char[nbytes];
    inFile.open(src, ios::in | ios::out | ios::binary);
    inFile.seekg (0, ios::end);
  
    int fileSize=inFile.tellg();
      inFile.seekg (0, ios::beg);
   
    if(nbytes<=fileSize)
    {
         inFile.read(msg,nbytes-1);
         cout<<msg<<endl;
         outFile << msg<<endl;                    
    }
    else
        cout<<"Required size is greater than filesize"<<endl;
    inFile.close();
    outFile.close();
}

 

I was traying to edit my thread but it seems iam not be abel to edit it .any way my question is fisrt when I copy the file myprogram test1.txt test2.txt. in the second case myprogram test1.txt the offset the length test2.txt. I hope this is clear now.