C++ 如何在循环中向空向量添加元素？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/17984268/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
how do i add elements to an empty vector in a loop?
提问by Amber Roxanna
I am trying to create an empty vector inside a loop and want to add an element to the vector each time something is read in to that loop.
我正在尝试在循环内创建一个空向量，并希望在每次将某些内容读入该循环时向该向量添加一个元素。
#include <iostream>
#include <vector>
using namespace std;
int main()
{
std::vector<float> myVector();
float x;
while(cin >> x)
myVector.insert(x);
return 0;
}
but this is giving me error messages.
但这给了我错误信息。
回答by Mark Garcia
You need to use std::vector::push_back()instead:
您需要std::vector::push_back()改用：
while(cin >> x)
myVector.push_back(x);
// ^^^^^^^^^
and not std::vector::insert(), which, as you can see in the link, needs an iterator to indicate the position where you want to insert the element.
而 not std::vector::insert()，正如您在链接中看到的那样，它需要一个迭代器来指示要插入元素的位置。
Also, as what @Joel has commented, you should remove the parentheses in your vector variable's definition.
此外，正如@Joel 所评论的那样，您应该删除向量变量定义中的括号。
std::vector<float> myVector;
and not
而不是
std::vector<float> myVector();
By doing the latter, you run into C++'s Most Vexing Parseproblem.
通过执行后者，您会遇到 C++最烦人的解析问题。
回答by Yang
Use push_back:
使用push_back：
while(cin >> x)
myVector.push_back(x);
The insertfunction takes an iterator as the first argument, indicating the position to insert.
该insert函数将迭代器作为第一个参数，指示要插入的位置。
Also, you need to get rid of the parentheses in the declaration of myVector:
此外，您需要去掉以下声明中的括号myVector：
std::vector<float> myVector;
回答by Nikunj
If you want to use myVector.insert(),
use it like myVector.insert(myVector.end(), x). This will append x at the end of myVector.
You can insert x in the beginning by myVector.insert(myVector.begin(), x).
如果你想使用myVector.insert()，就像使用它一样myVector.insert(myVector.end(), x)。这将在 myVector 的末尾附加 x。您可以在开头插入 x myVector.insert(myVector.begin(), x)。
回答by J-Alex
Another option is to use std::vector::emplace_back()instead of std::vector::push_back(). The makes some optimizations and doesn't take an argument of type vector::value_type, it takes variadic arguments that are forwarded to the constructor of the appended item, while push_backcan make unnecessary copies or movements.
另一种选择是使用std::vector::emplace_back()而不是std::vector::push_back(). 进行了一些优化并且不接受 type 参数vector::value_type，它接受传递给附加项的构造函数的可变参数，同时push_back可以进行不必要的复制或移动。
This is demonstrated in the std::vector::emplace_backdocumentation and hereis a related question.
这在std::vector::emplace_back文档中得到了证明，这里有一个相关的问题。
Usage example:
用法示例：
std::vector<int> myVector;
while (cin >> x) {
myVector.emplace_back(x);
}
