urgent : xp_cmdshell and user defined function

Hello.
I have got an executable function which have the following prototype:
char * Main( int arg c, char *argv[])
As you can see, It must return a string.
I would like to get this string in a user defined function, which calls the extended stored procedure xp_cmdshell, so that I'll be able to use a select statement to retrieve this string.
If I could have an explicit example, it would be very helpful for me.
I am looking forward to receiving suggestions.
Thank you very much.