Write a C++ main() function that reads double numbers from a file called "in.dat" until it reaches the end-of-file, and prints the number on cout with a width of 6 using 3 digits after the decimal point. Be sure to show any required #include directives. If the file fails to open, print out an error message "Error opening file" and exit the program with a failure.

The file can be of random numbers and the result from the program should be like this: 123123.567