Thread: header files

<somefile.h> includes from the compiler include directories.
"somefile.h" includes from the relative directory to the file that is calling it.

<somefile.h> includes from the compiler include directories.
"somefile.h" includes from the relative directory to the file that is calling it.

Not necessary. In the project you can specify several include directories that compiler will search for include files... It's a good practice to distinct standard includes from project file includes using <> and "" syntax

Update
Here is what msdn says:

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.

And here's what the standard says:

Code:

2 A preprocessing directive of the form
          # include <h-char-sequence> new-line
  searches a sequence of  implementation-defined  places  for  a  header
  identified  uniquely  by  the  specified  sequence between the < and >
  delimiters, and causes the replacement of that directive by the entire
  contents  of  the  header.  How the places are specified or the header
  identified is implementation-defined.

3 A preprocessing directive of the form
          # include "q-char-sequence" new-line
  causes the replacement of that directive by the entire contents of the
  source  file identified by the specified sequence between the " delim-
  iters.  The named source file is searched for  in  an  implementation-
  defined  manner.   If  this  search is not supported, or if the search
  fails, the directive is reprocessed as if it read
          # include <h-char-sequence> new-line
  with the identical contained sequence (including > characters, if any)
  from the original directive.

In other words, nothing much. In theory, every compiler is free to do whatever it wants, as long as it documents it.

MS's documentation pretty much is the established convention, except that it is redundant: the quoted form could omit the part about /I and INCLUDE, because the standard says that if the method of the quoted form fails, the method of the angle-bracket form must be tried.