Starting an application under windows using start

Answer 1

I believe start uses the file handler associated with the file's extension.

Basically it will use the files extension to lookup what application to run.
It sounds like the extension to the files you are using are resulting in a default handler of the console being started.

You could start by reading the MS documentation:
http://msdn.microsoft.com/en-us/library/53ezey2s.aspx

Answer 2

If the first parameter on the start command line is enclosed in double-quotes, it uses that as the window title instead of the command. It's lame, but that's what it does...

Try

string st = string("start \"\" \"")+std_str+string("\"");

instead.

But if you're trying to get the shell handler for a file to execute from within your process, a better, cleaner way to do this instead of invoking the start command is to use the ShellExecute() or ShellExecuteEx() Win32 API.