Detailed explanation of C++ member functions: underlying implementation and compilation process of object methods

Member functions in C are object methods attached to the class and are used to operate data members in the object. The compilation process includes: instantiation: creating a function pointer for each member function and storing it in the object; calling mechanism: the compiler automatically inserts code similar to result = ((_this)->*MemberFunction())(Arguments); ;Compilation process: preprocessing, compilation, assembly and linking to form an executable file.

Detailed explanation of C member functions: the underlying implementation and compilation process of object methods

Introduction

Member functions in C are methods attached to objects of a class and are used to operate the data members of the object. Understanding the underlying implementation of member functions and the compilation process is critical to a deep understanding of C programming.

Instantiation

When the compiler instantiates a class, it creates a function pointer for each member function that points to the function implementation in the class. Each object's function pointer is stored in that object's memory space.

Code Example

class MyClass {
public:
    int add(int a, int b) { return a + b; }
};

int main() {
    MyClass object;
    int result = object.add(10, 20); // 调用成员函数
    return 0;
}

After compiling this code, the compiler will create a function pointer for the add() member function and store it In object object. When the add() method is called, it calls the function indirectly using a function pointer.

Calling mechanism

When an object calls a member function, the compiler automatically inserts code similar to the following:

result = ((_this)->*MemberFunction())(Arguments);

Among them:

• _this refers to the current object.
• MemberFunction is the member function to be called.
• Arguments are the parameters of the member function.

Compilation process

1. Preprocessing: The compiler parses macros and preprocessor directives into the code.
2. Compilation: The compiler parses the code into assembler.
3. Assembly: The assembler converts assembler into machine code.
4. Linking: The linker links the machine code together with any required libraries to form the final executable file.

Practical case

Consider the following class for calculating the area of ​​a circle:

class Circle {
public:
    double radius;
    
    double getArea() {
        return radius * radius * 3.14159;
    }
};

In the main() function , we can call the getArea() member function for the object:

int main() {
    Circle circle;
    circle.radius = 5;
    double area = circle.getArea(); // 调用成员函数
    return 0;
}

After compilation, the compiler will create a function pointer for getArea() and store it in the circle object. When circle.getArea() is called, the function will be called indirectly using a function pointer to calculate and return the area of ​​the circle.

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