I like to put all my #includes in my header file then only include my header for that source file in my source file. What is the industry standard? Are there any draw backs to my method?
Definition of include transitive verb. 1 : to take in or comprise as a part of a whole or group. 2 : to contain between or within two sides and the included angle.
Including is defined as containing. If you invite the whole class, even the kid you do not like, this is an example of when you invite the class including the kid you don't like. Such as, among which; introducing one or more parts of the group or topic just mentioned.
You use including to introduce examples of people or things that are part of the group of people or things that you are talking about. Stars including Joan Collins are expected to attend. ... many conditions, including allergies, hyperactivity and tooth decay.
Generally, you only want to put the minimum necessary includes into a class header file, as anyone else who uses that header will be forced to #include
all of them too. In larger projects, this leads towards slower builds, dependency issues, and all sorts of other nastiness.
Think of a header file as the public interface to your class. You don't want to saddle everyone who uses it with extra dependencies, unless they're necessary to be able to use the class.
Move anything that's only needed in the class implementation down into the source file. For other classes used in a header, only #include
their headers if you actually need to know their size or contents in the header - anything else and a forward declaration is sufficient. Most cases, you only need to #include
classes you're inheriting from, and classes whose objects are value members of your class.
This page has a good summary. (Replicated below for reference)
Large software projects require a careful header file management even when programming in C. When developers move to C++, header file management becomes even more complex and time consuming. Here we present a few header file inclusion patterns that will simplify this chore.
Here, we discuss the basic rules of C++ header file inclusion needed to simplify header file management.
A header file should be included only when a forward declaration would not do the job. The header file should be so designed that the order of header file inclusion is not important. This is achieved by making sure that x.h
is the first header file in x.cpp
The header file inclusion mechanism should be tolerant to duplicate header file inclusions. The following sections will explain these rules with the help of an example.
The following example illustrates different types of dependencies. Assume a class A with code stored in a.cpp
and a.h
.
a.h
#ifndef _a_h_included_ #define _a_h_included_ #include "abase.h" #include "b.h" // Forward Declarations class C; class D; class A : public ABase { B m_b; C *m_c; D *m_d; public: void SetC(C *c); C *GetC() const; void ModifyD(D *d); }; #endif
a.cpp
#include "a.h" #include "d.h" void A::SetC(C* c) { m_c = c; } C* A::GetC() const { return m_c; } void A::ModifyD(D* d) { d->SetX(0); d->SetY(0); m_d = d; }
Lets analyze the header file inclusions, from the point of view of classes involved in this example, i.e. ABase
, A
, B
, C
and D
.
ABase
is the base class, so the class declaration is required to complete the class declaration. The compiler needs to know the size of ABase
to determine the total size of A
. In this case abase.h
should be included explicitly in a.h
.A
contains Class B
by value , so the class declaration is required to complete the class declaration. The compiler needs to know the size of B to determine the total size of A
. In this case b.h
should be included explicitly in a.h
.Class C
is included only as a pointer reference. The size or actual content of C
are not important to a.h
or a.cpp
. Thus only a forward declaration has been included in a.h
. Notice that c.h
has not been included in either a.h
or a.cpp
.D
is just used as a pointer reference in a.h
. Thus a forward declaration is sufficient. But a.cpp
uses class D
in substance so it explicitly includes d.h
.Header files should be included only when a forward declaration will not do the job. By not including c.h
and d.h
other clients of class A
never have to worry about c.h
and d.h
unless they use class C and D by value. a.h
has been included as the first header file in a.cpp
This will make sure that a.h
does not expect a certain header files to be included before a.h
. As a.h
has been included as the first file, successful compilation of a.cpp
will ensure that a.h
does not expect any other header file to be included before a.h
. If this is followed for all classes, (i.e. x.cpp
always includes x.h
as the first header) there will be no dependency on header file inclusion. a.h
includes the check on preprocessor definition of symbol _a_h_included_
. This makes it tolerant to duplicate inclusions of a.h
.
Cyclic dependency exists between class X
and Y
in the following example. This dependency is handled by using forward declarations.
#x.h and y.h
#
/* ====== x.h ====== */ // Forward declaration of Y for cyclic dependency class Y; class X { Y *m_y; ... }; /* ====== y.h ====== */ // Forward declaration of X for cyclic dependency class X; class Y { X *m_x; ... };
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