Comprehensive analysis of parameter passing methods of C++ functions

C is an excellent programming language with powerful functions and flexible syntax. In C programming, we often need to pass parameters to functions. When passing parameters, the parameter passing method becomes a very important issue. This article will comprehensively analyze the differences in parameter passing methods of C functions, including passing by value, passing by reference, and passing by pointer.

1. Parameter passing by value method

In C, when we pass parameters to a function, parameter passing by value is the most common method. Parameter passing by value means that when calling a function, the value of the actual parameter is copied to the variable of the corresponding formal parameter in the function definition. Operations on formal parameters in a function do not affect actual parameters.

Below we use a piece of code to show the characteristics of the value parameter passing method:

#include<iostream>
using namespace std;

void changeValue(int x){
    x = 10;
}

int main() {
    int num = 5;
    cout << "Before calling the function: " << num << endl;
    changeValue(num);
    cout << "After calling the function: " << num << endl;
    system("pause");
    return 0;
}

After running the program, the output is as follows:

Before calling the function: 5
After calling the function: 5

As can be seen from the output result, in The function changeValue() internally sets the value of the x variable to 10, but after the function is executed, the value of the num variable is still 5. This shows that in the pass-by-value parameter passing method, modifications to the formal parameters will not affect the actual parameters. .

2. Parameter passing method by reference

Reference is an important data type in C. A reference variable can be regarded as an alias of another existing variable. They share the same address. , changes made to one variable will also have an impact on the other variable. Parameter passing by reference refers to passing the reference of the actual parameter to the corresponding formal parameter to call the function. When the function is executed, the parameter passed is actually a reference to the memory address where the actual parameter is located. At this time, the actual parameter and the formal parameter point to the value of the same address.

Below we use a piece of code to show the characteristics of the parameter passing method:

#include<iostream>
using namespace std;

void changeValue(int &x){
    x = 10;
}

int main() {
    int num = 5;
    cout << "Before calling the function: " << num << endl;
    changeValue(num);
    cout << "After calling the function: " << num << endl;
    system("pause");
    return 0;
}

After running the program, the output is as follows:

Before calling the function: 5
After calling the function: 10

As can be seen from the output result, through In the parameter passing method, the function modifies the value of the actual parameter to 10 and also modifies the value of num. This shows that when passing parameters by reference, modifications to the formal parameters will affect the actual parameters.

3. Pointer parameter passing method

Pointer is also a very important data type in C. It can store a memory address and access the data in the memory address through a pointer. The pointer parameter passing method means that in a function call, the address of the actual parameter variable is passed to the formal parameter pointer variable in the function, and the function accesses the actual parameter variable through the pointer.

Below we use a piece of code to show the characteristics of the pointer parameter passing method:

#include<iostream>
using namespace std;

void changeValue(int *x){
    *x = 10;
}

int main() {
    int num = 5;
    cout << "Before calling the function: " << num << endl;
    changeValue(&num);
    cout << "After calling the function: " << num << endl;
    system("pause");
    return 0;
}

After running the program, the output is as follows:

Before calling the function: 5
After calling the function: 10

As can be seen from the output result, through In the pointer parameter passing method, the function modifies the value of the actual parameter to 10 and also modifies the value of num. This shows that in the pointer parameter passing mode, modifications to the formal parameters will affect the actual parameters.

4. Passing constant values, constant references and constant pointers

Passing constant values, constant references and constant pointers are also several ways to pass C function parameters. Their characteristics are in the first three ways. On the basis of this, the data protection function is added. Passed constant values, constant references, and constant pointers cannot be modified. They prevent functions from modifying the values ​​or addresses of actual parameters.

Below we use a piece of code to show the characteristics of passing constant values, constant references and constant pointers:

#include<iostream>
using namespace std;

//传常量值
void getValue(const int x){
    //x = 10;   //报错，无法改变常量值
    cout << "The value of x is: " << x << endl;
}

//传常量引用
void getNum(const int &x){
    //x = 10;   //报错，无法改变常量引用
    cout << "The value of x is: " << x << endl;
}

//传常量指针
void setNum(const int *x){
    //*x = 10;   //报错，无法改变常量指针
    cout << "The value of x is: " << *x << endl;
}

int main() {
    int num = 5;

    //传常量值
    getValue(num);

    //传常量引用
    getNum(num);

    //传常量指针
    const int *ptr = &num;
    setNum(ptr);

    system("pause");
    return 0;
}

After running the program, the output is as follows:

The value of x is: 5
The value of x is: 5
The value of x is: 5

From the output results, you can You can see that no matter whether you pass a constant value, a constant reference or a constant pointer, you cannot change the value of the actual parameter.

To sum up, the parameter passing methods of C function include passing by value, passing by reference and passing by pointer. Different methods have different characteristics and application scenarios. In the actual programming process, it needs to be based on Choose the appropriate parameter transfer method according to the actual situation. At the same time, passing constant values, constant references and constant pointers are also commonly used in C function programming. They can protect the data from being modified and improve the reliability and stability of the program.

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