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How to analyze the C++ keyword in C++, I believe that many inexperienced people are at a loss about it. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

In C++ language, then summed up many C++ keywords, if you do not use frequent references, pointers, you must use const_cast to turn, the constant pointer to the character char is often used to express strings, such as LPCSTR in windows is const char *.

1. Modifier constant

The most basic usage is to modify a variable with const to indicate that it is a constant, which can be used instead of a macro definition in C language. Note that it is initialized at declaration time, or in the initialization list of the constructor if it is a data member of the class.

Const int astat999; / / defines the constant an instead of the macro definition / / const int b; / / error. When defining a constant, you don't have to initialize extern const int c; / / externally defined constants without initializing int const diter0; / / is equivalent to const int, but the writing habit is different, but the writing habit is different. / / similarly, replace int with char, long, and the class is the same class Cls {public: Cls (int a _ int b): _ a (a) / / constant member initializes {_ binitib in the initialization list;} private: const int _ a; int _ b;}

two。 Modifier reference, pointer

Use a constant pointer to a reference or pointer to a C++ keyword, that is, you cannot modify the variable referenced or pointed to. If you do not use frequent references and pointers, you must convert them with const_cast. A constant pointer to the character char is often used to represent a string, such as LPCSTR in windows is const char *.

The content of const int & const int; / / a cannot be changed, so g (reference to a) is also const / / int & i=const_cast; / / error int & i=const_cast (a); / / use const_cast () to convert a constant to a non-constant int const & const int; / / equivalent to const int &, but with different writing habits. / / the content of / a cannot be changed, so k (pointer of a) is also const int const * string2; / / equivalent to const int *, but with different writing habits; / / error const char * n = "string"; / / string "string" internal characters cannot be changed char * o = "string2"; / / string "string2" can be modified

3. Decorated object

If you are decorating an object, it means that the data members of the object are constants and can only call the object's constant member functions, as explained later. Combining articles 1, 2, and 3, the const modifier indicates that the modified area of memory is locked and cannot be modified.

A common reference to an object is often used to pass parameters to a function. When the parameter of a function is an object, passing the parameter directly by value will call the object copy constructor and copy the object, which affects the efficiency of the program. Therefore, parameters are generally passed by reference. In order not to change the passed parameters, const is added to indicate that it is a frequent reference.

The content of const int & const int; / / a cannot be changed, so g (reference to a) is also const / / int & i=const_cast; / / error int & i=const_cast (a); / / use const_cast () to convert a constant to a non-constant int const & const int; / / equivalent to const int &, but with different writing habits. / / the content of / a cannot be changed, so k (pointer of a) is also const int const * string2; / / equivalent to const int *, but with different writing habits; / / error const char * n = "string"; / / string "string" internal characters cannot be changed char * o = "string2"; / / string "string2" can be modified

4. Another way for const to modify pointers

That is, the difference between the famous const char * and char * const. As const char* said earlier, it means constant pointer, and the area of memory referred to by char* cannot be modified to represent a string. And char * const means that the position pointed by the pointer cannot be modified, and the C++ keyword means that the pointer cannot point to other memory regions, which is very similar to references, char * const is equivalent to char &, so often reference const char & equivalent to const char * const, that is, who the pointer points to is immutable, and the content that the pointer points to is immutable. Notice whether const is written before or after *. This is the difference between * *. Char const * means the same as const char *.

After reading the above, have you mastered the method of how to analyze the C++ keyword in C++? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

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