Different compilers treat the two types of includes:
#include "filename" and #include <filename>
Differently in the details, but if you are programming for portability there is a simple rule of thumb to keep in mind: use the <> version to reference installed files, not local files. We will illustrate the reasoning for using the #include "" format in your library’s header files below.
myproject
src
project.cpp
include
myproject
project.hpp project_core.hpp
project.cpp source:
//project.cpp
//We need to include our local project.hpp file, which is not yet installed
//the compiler will use a command line similar to the following:
//gcc src/project.cpp -I include/
#include "myproject/project.hpp"
// do stuff`
project.hpp source:
#ifndef __PROJECT_HPP__
#define __PROJECT_HPP__
//project.hpp
//We need to include project_base.hpp, and we have 3 options:
// #include <project_base.hpp>
// This version would require that include/myproject be in the compiler's include path
// this is a bit annoying because it would require the user of your installed package to find
// the exact path the includes were installed in
// #include <myproject/project_base.hpp>
// This version requires that the project includes *always* be installed in a folder
// named "myproject"
// This requirement may make testing and test-installs harder.
// #include "project_base.hpp"
// This is the version we will choose because (at least on some compilers)
// the "" version of the include uses relative path lookups.
// this means that we can install our project's .hpp files anywhere we like and the
// project.hpp file will always be able to find its include for project_base.hpp
// _as long as they are installed in the same folder_ #include "project_base.hpp"
//do stuff #endif`
project_base.hpp source:
```cpp
#ifndef __PROJECT_BASE_HPP__
#define __PROJECT_BASE_HPP__
//project_base.hpp
//Not much to see here
//do stuff
#endif
When you go to actually use your installed library you will want to use the <> format: testmyproject.cpp source:
#include <myproject/project.hpp>
//Use the library
If we define the project as shown above and install in a standard location, compiling our testmyproject.cpp file is simple: ` gcc -I/usr/local testmyproject.cpp`
If, however, we use a different method of including project_base.hpp from project.hpp, our compilation is complicated: The additional include directory is necessary if we fail to follow the suggestions above because we have to help the compiler find all of the include paths we used. gcc -I/usr/local -I/usr/local/myproject testmyproject.cpp