The C++ structure pointer is used as a function parameter, and the value of the actual parameter will not be modified?
foreword
I recently learned C++ pointers and structures. I remember that when a function passes parameters, if the formal parameters pass pointers, the value of the actual parameter can be modified.
But today I saw an array of structures passed into a function as a formal parameter, but the value of the actual parameter was successfully modified. I feel very doubtful?
example
#include<iostream>
using namespace std;
//英雄结构体
struct hero
{
string name;
int age;
string sex;
};
void changeArray(hero arr[])
{
arr[0].name = "猪猪侠";
}
//打印数组
void printHeros(hero arr[], int len)
{
for (int i = 0; i < len; i++)
{
cout << "姓名： " << arr[i].name << " 性别： " << arr[i].sex << " 年龄： " << arr[i].age << endl;
}
}
int main() {
struct hero arr[5] =
{
{
"刘备",23,"男"},
{
"关羽",22,"男"},
{
"张飞",20,"男"},
{
"赵云",21,"男"},
{
"貂蝉",19,"女"},
};
//获取数组元素个数
int len = sizeof(arr) / sizeof(hero);
printHeros(arr, len);
changeArray(arr);
cout << "=============" << endl;
printHeros(arr, len);
system("pause");
return 0;
}
姓名： 刘备 性别： 男 年龄： 23
姓名： 关羽 性别： 男 年龄： 22
姓名： 张飞 性别： 男 年龄： 20
姓名： 赵云 性别： 男 年龄： 21
姓名： 貂蝉 性别： 女 年龄： 19
=============
姓名： 猪猪侠 性别： 男 年龄： 23
姓名： 关羽 性别： 男 年龄： 22
姓名： 张飞 性别： 男 年龄： 20
姓名： 赵云 性别： 男 年龄： 21
姓名： 貂蝉 性别： 女 年龄： 19
reason
When writing C++, when an array is passed in as a function parameter, the array is automatically converted into a pointer variable.
#include<iostream>
using namespace std;
void printArr(int arr[])
{
cout << *arr << endl;
arr++; // 正确
cout << *arr << endl;
cout << arr[1] << endl;
arr[1] = 0;
cout << arr[1] << endl;
};
int main() {
int arr[] = {
1,2,3}; // arr++; 这里错误
printArr(arr);
system("pause");
return 0;
}
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Therefore, when the formal parameter group is modified inside the function, the actual parameters will also change.
yet another
I recently learned C++ pointers and structures. I remember that when a function passes parameters, if the formal parameters pass pointers, the value of the actual parameter can be modified.
But today I saw a question about passing a structure into a function as a pointer, but failed to modify the value of the actual parameter.
#include<iostream>
using namespace std;
//英雄结构体
struct hero
{
string name;
int age;
string sex;
};
void printArr(int arr[])
{
cout << *arr << endl;
arr++; // 正确
cout << *arr << endl;
cout << arr[1] << endl;
arr[1] = 0;
cout << arr[1] << endl;
};
void show(hero p) {
cout << "结构体形参传递:" << endl;
cout << p.name << endl;
p.name = "猪猪侠";
cout << p.name << endl;
}
void show2(hero * p) {
cout << "结构体指针传递:" << endl;
cout << p->name << endl;
p->name = "猪猪侠";
cout << p->name << endl;
}
int main() {
int arr[] = {
1,2,3}; // arr++; 这里错误
printArr(arr);
struct hero p = {
"刘备",23,"男"};
show(p); // 刘备
cout << "结构体实参:" << endl;
cout << p.name << endl; // 实参未变
// 报错
show2(&p); // 刘备
cout << "结构体实参:" << endl;
cout << p.name << endl; // 实参未变
system("pause");
return 0;
}
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结构体形参传递:
刘备
猪猪侠
结构体实参:
刘备
结构体指针传递:
刘备
猪猪侠
结构体实参:
猪猪侠
But this article does not understand the problem that the structure pointer in C++ is used as a function parameter and will not modify the value of the actual parameter ! My test should be able to modify the value of the actual parameter.
To be studied!
Reference : Link
come on!
grateful!
effort!