C++ syntax error: The default value of a member variable is syntax incorrect. How to correct it?

In C programming, member variables are one of the important parts of a class. When declaring and defining class member variables, we can specify their default values ​​to avoid additional assignment operations in subsequent code. However, sometimes when specifying default values ​​for member variables, we may make some syntax errors, causing the compiler to fail to parse the code correctly. This article will introduce some common C member variable default value syntax errors and provide some solutions.

1. Syntax of default value of member variables

In C, we can specify their default value through the equal sign when declaring or defining class member variables. For example:

class Person {
public:
    string name = "Tom";
    int age = 18;
    double height = 175.0;
};

In this example, we define a class named Person, which contains three member variables: name, age and height. Each member variable has its default value specified using the equal sign. If we create a Person object but do not initialize any member variables, they will be initialized to "Tom", 18, and 175.0 respectively.

2. Common syntax errors in default value of member variables

Although it is easy to specify the default value of member variables in C, if we accidentally make some syntax errors, the compiler may cause errors. . The following are some common examples of syntax errors in the default value of member variables:

1. The type "string" of the data member "name" appears too early

class Person {
public:
    name = "Tom"; //错误: 数据成员“name”的类型“string”太早出现
    string name;
    int age = 18;
    double height = 175.0;
};

In this example, we are using The name variable is assigned a value before, but the type (string) that defines it appears later. To avoid this error, we should first define the type of the variable and then use the equal sign to specify its default value.

2. Only "=" is allowed for default member initialization

class Person {
public:
    string name("Tom"); //错误：默认成员初始化只允许使用“=”
    int age = 18;
    double height = 175.0;
};

In this example, we use brackets to initialize the default value of the variable name, but this method is wrong. In C, any initialization method other than using the equal sign to specify the default value of a member variable is wrong. Therefore, we should use the equal sign to specify a default value for the variable name.

3. Duplicate member variable default values

class Person {
public:
    string name = "Tom";
    int age = 18;
    double height = 175.0;
    string name = "Jack"; //错误: 重复的成员变量默认值
};

In this example, we define two member variables with the same name and specify different default values ​​for them. This is wrong because C does not allow us to define two variables with the same name in the same class. To avoid this error, we should check carefully and avoid defining variables repeatedly.

3. How to avoid grammatical errors in the default value of member variables

In order to avoid grammatical errors in the default value of member variables, we need to follow the following suggestions:

1. When defining a variable, first specify the variable type, and then use the equal sign to specify the default value.

2. Only use the "=" operator to specify the default value of the member variable.

3. Avoid repeatedly defining member variables with the same name.

4. When defining class member variables, check carefully to make sure there are no syntax errors. If so, fix them promptly.

In short, the default value of member variables in C is very useful, but you need to be careful when using it to avoid making syntax errors. By carefully studying the syntax rules of C and strictly following these rules, we can avoid most common syntax errors when defining class member variables, and bring better readability, maintainability and safety to our programs. stability.

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