The /out switch specifies the default directory where the MIDL compiler writes output files.
midl /out path-specification
Specifies the path to the directory in which the stub, header, and switch files are generated. A drive specification, an absolute directory path, or both can be specified. Paths can be explicitly quoted using double quotes (") to prevent the shell from interpreting the special characters.
The output directory can be specified with a drive letter, an absolute path name, or both. The /out option can be used with any of the switches that enable individual output file specification.
When the /out switch is not specified, files are written to the current directory.
midl /out c:\mydir\mysubdir\subdir2 deeper filename.idl
midl /out c: filename.idl
midl /out \mydir\mysubdir\another filename.idl