Question

我想创建一个动态指针数组，每个指针指向一个结构。在程序中有一个添加结构的选项，如果计数器到达数组的最后一个值，则数组会扩展。

struct student
{
    string id;
    string name;
};

int N=5;
int counter=0;
student **big=new student *[N]; //a ptr to an array of ptr's.

void add_student (int &counter,student **big)
{
    int i;

    if (counter==0)
    {
        for (i=0; i<N; i++)
        {
            big[i]=new student; 
        }
    }

    if (counter==N)
    {
        N+=5;
        student **temp=new student *[N];
        for (i=counter-1; i<N; i++)
        {
            temp[i]=new student;
        }

        for (i=0; i<counter; i++)
        {
            temp[i]=big[i];
        }

        delete [] big;
        big=temp;
    }

    cout<<"Enter student ID: "<<endl;
    cin>>(*big)[counter].id;

    cout<<"Enter student name: "<<endl;
    cin>>(*big)[counter].name;

    counter++;
}

当我运行该程序时，在我尝试添加多个学生后它崩溃了。谢谢！

Answer 1

试试这段代码。主要问题是你写(*big)[counter].id而没有这个有效的记忆。在下面的函数中，首先创建一个student对象，然后写入。

PS：我没有测试过代码，请告诉我它是否有问题。

struct student {
  string id;
  string name;
};

int N=5;
int counter=0;
student **big = new student *[N]; //a ptr to an array of ptr's.

// Variable big and counter is global, no need to pass as argument.
void add_student (student *new_student) {
    // Resize if needed
    if (counter==N) {
        int i;

        student **temp=new student *[N+5];

        // Copy from the old array to the new
        for (i=0; i<N; i++) {
            temp[i]=big[i];
        }

        // Increase maximum size
        N+=5;

        // Delete the old
        delete [] big;
        big=temp;
    }

    // Add the new student
    big[counter] = new_student; 

    counter++;
}

// Function called when we should read a student
void read_student() {
    student *new_student = new student;

    cout<<"Enter student ID: "<<endl;
    cin>>new_student->id;

    cout<<"Enter student name: "<<endl;
    cin>>new_student->name;

    // Call the add function
    add_student (new_student);
}

Answer 2

我刚试过。错误是因为您没有正确处理指向结构的指针。传递一个指向某事物的指针意味着该函数可以改变指针地址，而不仅仅是它指向的东西。所以在函数中声明一个指向指针的指针是可以的，但是声明p到p的全局p没有多大意义。使用＆amp; ptr可以达到相同的效果。对于p到p到s，即将指针的地址传递给函数。我做了一些改变，但我不确定它是否有效。我会在4/5小时后再试一次，并会详细检查问题。暂时请满足于以下内容。（可能是下面的一些错误所以要小心）

    struct student
    {
      string id;
      string name;
    };

    int N=5;
    int counter=0;
    student *big=new student[N]; //a ptr to an array of ptr's.

    void add_student (int &counter,student **ppBig)
    {
     int i;

    if (counter==0)
    {
     for (i=0; i<N; i++)
        *ppBig[i]=new student; 
    }

if (counter==N)
{
    N+=5;
    student *temp=new student [N];
    for (i=counter-1; i<N; i++)
        temp[i]=new student;

    for (i=0; i<counter; i++)
        temp[i]=*ppBig[i];

    delete[] *ppBig;
    ppBig=temp;
}


cout<<"Enter student ID: "<<endl;
cin>>(*big)[counter].id;

cout<<"Enter student name: "<<endl;
cin>>(*big)[counter].name;

counter++;

}

如何创建指向struct的指针数组的指针？

2 个答案: