Look at file associations

C:\temp>assoc .scx
.fle=fle_auto_file

C:\temp>ftype fle_auto_file
fle_auto_file="C:\myxapp\myapp.exe" "%1"

/steveA

Hi! I realize this is an old post, but I thought your question deserved some
additional explanation.

When you Open or Open With a file in Explorer, it invokes the application
you're opening it with, passing the file's full path as the first argument.
You can find this path by examining argv[1] in your main entry function -
but be careful if you invoke your program from the command-line, where you
will have to put quotes around the filename if it contains a space.

As for reading the contents of the file in as a string, if you have access
to the .NET Framework you can use StreamReader's member function ReadToEnd.
See this topic, which includes an example in C++:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlr
fsystemiostreamreaderclassreadtoendtopic.asp

If you cannot access the .NET Framework, or wish to port this code in the
future, you can accomplish the same thing in standard C++ using a function
like this one:

#include <fstream>
#include <iostream>
#include <string>

std::string ContentsToString(std::istream& in)
{
   std::string contents;
   char c;
   in.get(c);
   while(!in.eof()) {
       contents += c;
       in.get(c);
   }
   return contents;
}

int main(int argc, char* argv[])
{
   std::ifstream in(argv[1]);
   if (in) {
       std::cout << ContentsToString(in);
       in.close();
   }
   return 0;
}

I hope this helps.