A preprocessor statement to add a header file (.h or .hpp) or other files to your program.
There are three different header file #includes:
- include <iostream> // 1: STL
- include <assert.hpp> // 2: The standard header file directory
- include "Unit1.h" // 3: Local
The first, without the .h extension, means that this header file is from the Standard Template Library.
The second #include means that the header is not from the STL but in the standard header file directory.
The third #include means that the file is local, i.e. in the same directory as the program. If the local #include fails, the standard header file directory is checked for this header file.
The C style include on ?CppStl STL headers
For backwards compatibility with C one can [[CppInclude
- include]] C++ header files with the .h extension.
- include <stdio.h> //C-stle #include !!!
This header file is a wrapper: all it does is call the C++ header file cstdio and then adds a 'using namespace std', as C does not have namespaces.
This has the unfortunate side-effect that after calling such a header file all functions and classes in namespace std will be in the global namespace.
As it pollutes the global namespace, avoid using namespace std [4,5].
An example from :
vector v1; //Error: no 'vector' in global namespace
- include <vector> //Carefully avoids polluting the global namespace
vector v2; //Oops: this now works
- include <stdio.h> //Contains a 'using namespace std'.
Implementation (.c or .cpp) files
These normally are not #included. Instead, these are added to your project. For example, in C++ Builder, select 'Project | Add to Project'.
Forgetting to add an implementation file to you project results in a linking error.
last edited (December 3, 2006) by bilderbikkel
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