到目前为止,我对命名空间完全没问题,但是当涉及到头文件时
在完全合格的课程方面,事情变得低效
名称,使用指令和使用声明.

关于这个问题的一个很好的描述是Herb Sutter的this文章.

据我所知,这一切归结为：如果你总是写一个头文件
使用完全限定类型名称来引用其他名称空间中的类型.

这几乎是不可接受的.由于C头通常提供声明
在一个类中,最大可读性具有最高优先级.完全符合条件
最后,来自不同命名空间的类型会产生很多视觉噪音
将标题的可读性降低到提出问题的程度
是否要使用名称空间.

不过我想利用C命名空间,所以考虑一下
问题：如何克服C头文件的命名空间邪恶？后
一些研究我认为typedef可能是解决这个问题的有效方法.

下面你将找到一个C示例程序,它演示了我的意思
喜欢使用公共类作用域typedef从其他名称空间导入类型.
该程序在语法上是正确的,并在MinGW W64上编译良好.到目前为止
很好,但我不确定这种方法是否会愉快地删除using关键字
从标题但引入另一个我根本不知道的问题.
就像Herb Sutter描述的东西一样棘手.

那是我恳请所有对C有透彻了解的人
检查下面的代码,让我知道这是否有效.谢谢
为了你的想法.

MyFirstClass.hpp

#ifndef MYFIRSTCLASS_HPP_
#define MYFIRSTCLASS_HPP_
 
namespace com {
namespace company {
namespace package1 {
 
class MyFirstClass
{
public:
    MyFirstClass();
    ~MyFirstClass();
 
private:
 
};
 
} // namespace package1
} // namespace company
} // namespace com
 
#endif /* MYFIRSTCLASS_HPP_ */

MyFirstClass.cpp

#include "MyFirstClass.hpp"
 
using com::company::package1::MyFirstClass;
 
MyFirstClass::MyFirstClass()
{
}
 
MyFirstClass::~MyFirstClass()
{
}

MySecondClass.hpp

#ifndef MYSECONDCLASS_HPP_
#define MYSECONDCLASS_HPP_
 
#include <string>
#include "MyFirstClass.hpp"
 
namespace com {
namespace company {
namespace package2 {
 
    /*
     * Do not write using-declarations in header files according to
     * Herb Sutter's Namespace Rule #2.
     *
     * using std::string; // bad
     * using com::company::package1::MyFirstClass; // bad
     */
 
class MySecondClass{
 
public:
    /*
     * Public class-scoped typedefs instead of using-declarations in
     * namespace package2. Consequently we can avoid fully qualified
     * type names in the remainder of the class declaration. This
     * yields maximum readability and shows cleanly the types imported
     * from other namespaces.
     */
    typedef std::string String;
    typedef com::company::package1::MyFirstClass MyFirstClass;
 
    MySecondClass();
    ~MySecondClass();
 
    String getText() const; // no std::string required
    void setText(String as_text); // no std::string required
 
    void setMyFirstInstance(MyFirstClass anv_instance); // no com::company:: ...
    MyFirstClass getMyFirstInstance() const; // no com::company:: ...
 
private:
    String is_text; // no std::string required
    MyFirstClass inv_myFirstInstance; // no com::company:: ...
};
 
} // namespace package2
} // namespace company
} // namespace com
 
#endif /* MYSECONDCLASS_HPP_ */

MySecondClass.cpp

#include "MySecondClass.hpp"
 
/*
 * According to Herb Sutter's "A Good Long-Term Solution" it is fine
 * to write using declarations in a translation unit,as long as they
 * appear after all #includes.
 */
using com::company::package2::MySecondClass; // OK because in cpp file and
                                             // no more #includes following
MySecondClass::MySecondClass()
{
}
 
MySecondClass::~MySecondClass()
{
}
 
/*
 * As we have already imported all types through the class scoped typedefs
 * in our header file,we are now able to simply reuse the typedef types
 * in the translation unit as well. This pattern shortens all type names
 * down to a maximum of "ClassName::TypedefTypeName" in the translation unit -
 * e.g. below we can simply write "MySecondClass::String". At the same time the
 * class declaration in the header file now governs all type imports from other
 * namespaces which again enforces the DRY - Don't Repeat Yourself - principle.
 */
 
// Simply reuse typedefs from MySecondClass
MySecondClass::String MySecondClass::getText() const
{
    return this->is_text;
}
 
// Simply reuse typedefs from MySecondClass
void MySecondClass::setText(String as_text)
{
    this->is_text = as_text;
}
 
// Simply reuse typedefs from MySecondClass
void MySecondClass::setMyFirstInstance(MyFirstClass anv_instance)
{
    this->inv_myFirstInstance = anv_instance;
}
 
// Simply reuse typedefs from MySecondClass
MySecondClass::MyFirstClass MySecondClass::getMyFirstInstance() const
{
    return this->inv_myFirstInstance;
}

Main.cpp的

#include <cstdio>
#include "MySecondClass.hpp"
 
using com::company::package2::MySecondClass; // OK because in cpp file and
                                             // no more #includes following
int main()
{
    // Again MySecondClass provides all types which are imported from
    // other namespaces and are part of its interface through public
    // class scoped typedefs
    MySecondClass *lpnv_mySecCls = new MySecondClass();
 
    // Again simply reuse typedefs from MySecondClass
    MySecondClass::String ls_text = "Hello World!";
    MySecondClass::MyFirstClass *lpnv_myFirClsf =
            new MySecondClass::MyFirstClass();
 
    lpnv_mySecCls->setMyFirstInstance(*lpnv_myFirClsf);
 
    lpnv_mySecCls->setText(ls_text);
    printf("Greetings: %s\n",lpnv_mySecCls->getText().c_str());
 
    lpnv_mySecCls->setText("Goodbye World!");
    printf("Greetings: %s\n",lpnv_mySecCls->getText().c_str());
 
    getchar();
 
    delete lpnv_myFirClsf;
    delete lpnv_mySecCls;
 
    return 0;
}