What is the difference between #include <filename> and #include "filename"?

c++ c include header-files c-preprocessor
quest49 picture quest49 · Aug 22, 2008 · Viewed 632.7k times · Source

In the C and C++ programming languages, what is the difference between using angle brackets and using quotes in an include statement, as follows?

  1. #include <filename>
  2. #include "filename"

Answer

quest49 picture quest49 · Aug 22, 2008

In practice, the difference is in the location where the preprocessor searches for the included file.

For #include <filename> the preprocessor searches in an implementation dependent manner, normally in search directories pre-designated by the compiler/IDE. This method is normally used to include standard library header files.

For #include "filename" the preprocessor searches first in the same directory as the file containing the directive, and then follows the search path used for the #include <filename> form. This method is normally used to include programmer-defined header files.

A more complete description is available in the GCC documentation on search paths.

Related questions

Is the backslash acceptable in C and C++ #include directives?

There are two path separators in common use: the Unix forward-slash and the DOS backslash. Rest in peace, Classic Mac colon. If used in an #include directive, are they equal under the rules of the C++11, C++03, and C99 standards?

Read More
Detecting superfluous #includes in C/C++?

I often find that the headers section of a file get larger and larger all the time but it never gets smaller. Throughout the life of a source file classes may have moved and been refactored and it's very possible …

Read More
How to tell where a header file is included from?

How can I tell where g++ was able to find an include file? Basically if I #include <foo.h> g++ will scan the search path, using any include options to add or alter the path. But, at the …

Read More