C++ compilation error: The local type definition is invalid, what should I do?

In the process of C programming, compilation errors are often encountered, and these errors can be very confusing. This article will mainly discuss the C compilation error: "The local type definition is invalid, what should I do?"

In C programs, we often need to define a type within a class, such as a structure. This can be achieved by using the "typedef" keyword. For example:

class MyClass {
public:
    typedef struct {
        int x;
        int y;
    } Point;
    Point getPoint();
};

In the above program, we use "typedef" to define a structure "Point" and use it in the class "MyClass".

However, in some cases, using "typedef" will cause a compilation error: "The local type definition is invalid". This error is usually caused by using incorrect syntax when defining the type. When using "typedef" to define a structure, you should use the "struct" keyword to distinguish it from a class definition. The following is the correct way to write it:

class MyClass {
public:
    typedef struct Point {
        int x;
        int y;
    } Point;
    Point getPoint();
};

In the above program, the "struct" keyword tells the compiler that we want to define a structure, and the "typedef" keyword tells the compiler that we want to name this structure. for "Point". In this way, we can use the "Point" type in the class. In addition, we must place the definition of this structure before the class definition to avoid compilation errors.

Besides this, there are some other causes of "Invalid local type definition" error. Here are some common mistakes:

1. Using an unnamed structure or union within a class.

class MyClass {
public:
    struct {
        int x;
        int y;
    } Point; // 编译错误：本地类型定义无效
    Point getPoint();
};

In the above program, the "Point" structure is not named and cannot be used in the class definition. It should be named as follows:

class MyClass {
public:
    struct Point {
        int x;
        int y;
    } Point;
    Point getPoint();
};

2. A structure or union with the same name is defined within the class.

class MyClass {
public:
    typedef struct {
        int x;
        int y;
    } Point;
    Point Point; // 编译错误：本地类型定义无效
    Point getPoint();
};

In the above program, we have defined the same name for both the structure and the variables, which will cause a compilation error. They should be named separately:

class MyClass {
public:
    typedef struct {
        int x;
        int y;
    } Point;
    Point point;
    Point getPoint();
};

3. When using structures or unions within a class, the "struct" or "union" keywords are not used.

class MyClass {
public:
    typedef Point {
        int x;
        int y;
    } Point;
    Point getPoint(); // 编译错误：本地类型定义无效
};

In the above program, we did not use the "struct" or "union" keyword to define the "Point" structure, which will cause a compilation error. The "typedef" keyword by itself does not let the compiler know that this is a struct and that the correct syntax should be used:

class MyClass {
public:
    typedef struct {
        int x;
        int y;
    } Point;
    Point getPoint();
};

In summary, the C compile error "Invalid local type definition" is usually due to the use of incorrect syntax , or caused by defining an unnamed structure or union within the class. By using the "typedef" and "struct" keywords correctly, we can avoid these errors.

The above is the detailed content of C++ compilation error: The local type definition is invalid, what should I do?. For more information, please follow other related articles on the PHP Chinese website!