OldSchoolCode

"main" is the entry point for a c or c++ program. usually we declare it like this

void main( void ) or void main( )

the above version of main takes 0 arguments. there is another variation of main that takes 2 arguments...

 
int main( int argc, char *pArgv[] )

whoa what is this? the int argc is how many arguments were passed to main, and the pArgv is a pointer to the array of arguments. When main is declared in this format, and the user doubleclicks the exe - here it was happens: Windows passes 1 arguement to main, the name of the program. In this case

argc == 1
 
and pArgv[0] == "myProgram.exe"

neat I suppose, but not too useful. However, if a user drags a file over the program, then the second argument is the name and path of the dragged file.

Lets say the user drags "notes.txt" over myProgram.exe

then

argc == 2
 
pArgv[0] == "myProgram.exe"
pArgv[1] == "c:\notes.txt"

__________________________________________________________

#define _CRT_SECURE_NO_DEPRECATE   
 
#include <string.h>
#include <stdio.h>
#include <conio.h>

int main(int argc,char *pArgv[])
{
   printf( "\n Value received by argc is %d.\n", argc );
   printf( "\n There are %d command line arguments\n", argc );
   printf( " passed to main().\n" );
   printf( "\n The first command line argument is:\n" );
   printf( " %s\n", pArgv[ 0 ] );

   if ( argc == 2 )
   {
      printf( "\n The second command line argument is:\n" ); 
      printf( " %s\n", pArgv[ 1 ] );
   }
   
   else
   {
      printf( "Please drag your file across the exe. " );
   }
   
   getch( ); 

   return 0;
}

__________________________________________________________

#define _CRT_SECURE_NO_DEPRECATE   
 
#include <string.h>
#include <stdio.h>
 
int main(int argc,char *pArgv[])
{
   char sourceName[260];
   char destName[260];
   unsigned char byte;

   if (argc==2)
   {
      //This takes the filename of the file that
      //you drag onto the exe and copies the name
      //to sourceName
      strcpy( sourceName, pArgv[1] );

      //when you drag your file over the .exe, this 
      //program will create a new file and copy  
      //the original file and any data in it to
      //the same directory as the original. 
      //we can't use the same name so we will take the 
      //original text document name and add .duplicate.txt
      //to the end. Not pretty but good enough for now 
      sprintf( destName, "%s.duplicate", sourceName );

      //open the source file for reading and the destination
      //file for writing.
      FILE *pSource = fopen( sourceName, "rb" );
      FILE *pDest = fopen( destName, "ab" );
	
      //read one byte at a time from the source file
      //and place it at the address of "byte"
      //Will read until the end of the file "!= 0"
      while ( fread( &byte, sizeof(unsigned char), 1, pSource ) != 0 )
      {
         fwrite( &byte, sizeof(unsigned char), 1, pDest );
      }

      //close the open files
      fclose( pSource );
      fclose( pDest );
   }

   else
   {
      //if you double click the exe it will print this
      printf("\n\n Please drag and drop your file on the exe.\n\n ");
      printf("Press enter to exit this screen. ");
   }

    return 0;
}