C++ - The #include Directive

http://msdn.microsoft.com/en-us/library/36k2cdd4(v=vs.80).aspx

#include  "path-spec"
#include  <path-spec>

Syntax Form	Action
Quoted form	This form instructs the preprocessor to look for include files in the same directory of the file that contains the #include statement, and then in the directories of any files that include (#include) that file. The preprocessor then searches along the path specified by the /I compiler option, then along paths specified by the INCLUDE environment variable.
Angle-bracket form	This form instructs the preprocessor to search for include files first along the path specified by the /I compiler option, then, when compiling from the command line, along the path specified by the INCLUDE environment variable.