创建对象向量时，如何将参数传递给Default或Copy Constructor以初始化值? [英] When creating a vector of objects, how to pass arguments to Default or Copy Constructor to initialize values?

问题描述

对于我要为我的C ++类中的项目编写的程序，要求之一是使用构造函数初始化对象中的数据成员.

For a program I'm writing for a project in my C++ class, one of the requirements is to use constructors to initialize data members in objects.

我们还必须读取二进制文件.

We also have to read from binary files.

我选择完成此操作的方法是:

The method I chose to accomplish this was:

// Loads invmast.dat or creates one if none exists
fstream invFile;
invFile.open("invmast.dat", std::fstream::in);
if (!invFile)
{
    cout << "File invmast.dat not found, creating a new one." << endl;
    invFile.open("invmast.dat", std::fstream::out | std::fstream::app | std::fstream::binary);
    if (!invFile)
    {
        cerr << "Unable to create or open file invmast.dat; exiting." << endl;
        exit (EXIT_FAILURE);
    }
}
cout << "File invmast.dat opened successfully." << endl;

vector <InventoryItem> invMast;
//vector <InventoryItem>::iterator invMastIterator;

InventoryItem invLoader;

while ( invFile && !invFile.eof())
{
    invFile.read(reinterpret_cast<char *>(&invLoader), sizeof(invLoader));
    invMast.insert(invMast.begin(), invLoader);      
}

我更愿意创建一个对象向量，并将参数传递给副本或默认构造函数，但我似乎找不到找到这种方法的方法.

I'd prefer to create a vector of objects and pass the arguments to the copy or default constructor, but I can't seem to find a way to do this.

有没有办法，或者我需要重新考虑我的方法?

Is there a way, or do I need to rethink my approach?

谢谢！

推荐答案

如果您只是在构造元素，则可以使用

If you were simply constructing an element, you could use emplace_back to construct it directly in the vector:

invMast.emplace_back(some, constructor, parameters);

但是在这里，由于要从原始字节初始化 InventoryItem ，因此您可能只想构造一个对象并将其移至向量中:

But here, since you’re initialising the InventoryItem from raw bytes, you probably just want to construct an object and move it into the vector:

invFile.read(reinterpret_cast<char *>(&invMast.back()), sizeof(invLoader));
invMast.push_back(std::move(invLoader));

或者默认构造一个元素，然后填充它:

Or default-construct an element and then fill it:

invMast.emplace_back();
invFile.read(reinterpret_cast<char *>(&invMast.back()), sizeof(InventoryItem));

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