使用C ++访问结构数组的成员

Working through C++ Primer Plus and am trying to cin data to a dynamically allocated array of structures. One of the items is a char array. How do I write to these struct members? Posting code of my wrong attempt so you can see what I'm trying to do.

使用C ++ Primer Plus并尝试将数据cin到动态分配的结构数组。其中一个项目是char数组。我如何写这些结构成员?发布我错误尝试的代码,以便您可以看到我正在尝试做的事情。

    #include <iostream>
using namespace std;

struct contributions
{
    char name[20];
    double dollars;
};

int donors;

int main()
{
    cout << "How many contributors will there be?\n";
    cin >> donors;
    contributions * ptr = new contributions[donors];
    for(int i = 0; i <= donors; i++)
    {
        cout << "Enter donor name #" << i+1 << ": \n";
        cin >> ptr->contributions[i].name;
        cout << "Enter donation amount: \n";
        cin >> ptr->contributions[i].dollars;
    }

Thanks in advance!

提前致谢!

4 个解决方案

#1

Try using std::string instead of char[20] for name and the sample should work just fine.

尝试使用std :: string而不是char [20]作为名称,样本应该可以正常工作。

struct contributions
{
    std::string name;
    double dollars;
};

also change the access to

也改变了访问权限

ptr[i].name

#2

cin >> ptr[i].name;

ptr is the name of the variable, it is of type contributions*. It is an array of contributions, so to access the ith member, use ptr[i]. Then access the name field of that member via ptr[i].name. Also, cin >> char[] may not work (I don't recall for sure), as char[] is more of a C-ish thing, whereas cin is C++. So you might need to change the type of name to std::string.

ptr是变量的名称,它的类型为贡献*。这是一个贡献数组,所以要访问第i个成员,请使用ptr [i]。然后通过ptr [i] .name访问该成员的名称字段。此外,cin >> char []可能不起作用(我不记得肯定),因为char []更像是一个C-ish的东西,而cin是C ++。因此,您可能需要将名称类型更改为std :: string。

As an aside, convention is to name your structs/classes with a singular noun. Thus contribution would be a more correct name; every instance represents a single contribution.

顺便说一下,惯例是用单数名词命名你的结构/类。因此,贡献将是一个更正确的名称;每个实例代表一个贡献。

#3

cin >> ptr[i].name; (the correct form) would stop at the first whitespace character (and risk a buffer overflow if no such character comes before the 20 spaces in the array are exhausted). Use cin.getline(ptr[i].name, 20) instead.

cin >> ptr [i] .name; (正确的形式)将停在第一个空格字符处(如果在数组中的20个空格用尽之前没有这样的字符,则存在缓冲区溢出的风险)。请改用cin.getline(ptr [i] .name,20)。

#4

Also, using a std::vector of contributions w2ill make the code much simpler. as it is, you have a memory leak. If this is direct from C++ Primer Plus I'd seriously suggest changing to a text book that will teach you modern, correct C++, such as Accelerated C++ by Koenig & Moo.

此外,使用std :: vector of w2ill使代码更加简单。事实上,你有内存泄漏。如果这是直接来自C ++ Primer Plus,我会认真地建议改为教你现代正确的C ++的教科书,例如Koenig&Moo的Accelerated C ++。

#1