C/C++项目中.h和.inc文件区别

原问题：Difference between .h files and .inc files in c

C/C++的标准惯例是将class、function的声明信息写在.h文件中。.c文件写class实现、function实现、变量定义等等。然而对于template来说，它既不是class也不是function，而是可以生成一组class或function的东西。编译器（compiler）为了给template生成代码，他需要看到声明（declaration ）和定义（definition ），因此他们必须不被包含在.h里面。

为了使声明、定义分隔开，定义泻在自己文件内部，即.inc文件，然后在.h文件的末尾包含进来。当然除了.inc的形式，还可能有许多其他的写法.inc, .imp, .impl, .tpp, etc.

英文原版回答

.inc files are often associated with templated classes and functions.

Standard classes and functions are declared with a .h file and then defined with a .cpp file. However, a template is neither a class nor a function but a pattern that is used to generate a family of classes or functions. In order for the compiler to generate the code for the template, it needs to see both the declaration and definition and therefore they both must be included in the .h file.

To keep the declaration and definition separate, the definition is placed in its own file and included at the end of the .h file. This file will have one of many possible file extensions .inc, .imp, .impl, .tpp, etc.

Declaration example: 

// Foo.h
#ifndef FOO_H
#define FOO_H
 
template<typename T>
class Foo {
public:
    Foo();
    void DoSomething(T x);
private:
    T x;
};
 
#include "Foo.inc"
#endif // FOO_H

Definition example:

// Foo.inc
#include "Foo.h"
 
template<typename T>
Foo<T>::Foo() {
    // ...
}
 
template<typename T>
void Foo<T>::DoSomething(T x) {
    // ...
}

from：C/C++项目中.h和.inc文件区别