C++ 添加到对的向量

Adding to a vector of pair

提问by Richard

I have a vectorof pairlike such:

我有一个vector的pair像这样的：

vector<pair<string,double>> revenue;

I want to add a string and a double from a map like this:

我想从这样的地图中添加一个字符串和一个双精度值：

revenue[i].first = "string";
revenue[i].second = map[i].second;

But since revenue isn't initialized, it comes up with an out of bounds error. So I tried using vector::push_backlike this:

但由于收入未初始化，因此会出现越界错误。所以我尝试这样使用vector::push_back：

revenue.push_back("string",map[i].second);

But that says cannot take two arguments. So how can I add to this vectorof pair?

但这说不能有两个论点。那么，如何可以添加到这个vector的pair？

回答by avakar

Use std::make_pair:

使用std::make_pair：

revenue.push_back(std::make_pair("string",map[i].second));

回答by m47h

IMHO, a very nice solution is to use c++11 emplace_backfunction:

恕我直言，一个非常好的解决方案是使用 c++11 emplace_back函数：

revenue.emplace_back("string", map[i].second);

It just creates a new element in place.

它只是在适当的位置创建了一个新元素。

回答by Ed S.

revenue.pushback("string",map[i].second);

But that says cannot take two arguments. So how can I add to this vector pair?

但这说不能有两个论点。那么我怎样才能添加到这个向量对中呢？

You're on the right path, but think about it; what does your vector hold? It certainly doesn't hold a string and an int in one position, it holds a Pair. So...

你走在正确的道路上，但想想看；你的向量是什么？它当然不会在一个位置保存一个字符串和一个 int，它保存一个Pair. 所以...

revenue.push_back( std::make_pair( "string", map[i].second ) );     

回答by Hsu Hau

Or you can use initialize list:

或者您可以使用初始化列表：

revenue.push_back({"string", map[i].second});

回答by hochl

Read the following documentation:

阅读以下文档：

http://cplusplus.com/reference/std/utility/make_pair/

http://cplusplus.com/reference/std/utility/make_pair/

or

或者

http://en.cppreference.com/w/cpp/utility/pair/make_pair

http://en.cppreference.com/w/cpp/utility/pair/make_pair

I think that will help. Those sites are good resources for C++, though the latter seems to be the preferred reference these days.

我认为这会有所帮助。这些站点是C++ 的好资源，尽管后者似乎是最近的首选参考。

回答by Caner SAYGIN

revenue.push_back(pair<string,double> ("String",map[i].second));

this will work.

这会起作用。

回答by Sardeep Lakhera

You can use std::make_pair

您可以使用 std::make_pair

revenue.push_back(std::make_pair("string",map[i].second));

回答by Ritankar Paul

Using emplace_backfunction is way better than any other method since it creates an object in-place of type Twhere vector<T>, whereas push_backexpects an actual value from you.

使用emplace_backfunction 比任何其他方法都要好得多，因为它在Twhere类型的地方创建了一个对象vector<T>，而push_back期望来自您的实际值。

vector<pair<string,double>> revenue;

// make_pair function constructs a pair objects which is expected by push_back
revenue.push_back(make_pair("cash", 12.32));

// emplace_back passes the arguments to the constructor
// function and gets the constructed object to the referenced space
revenue.emplace_back("cash", 12.32);

回答by sarthak bansal

As many people suggested, you could use std::make_pair.

正如许多人建议的那样，您可以使用std::make_pair.

But I would like to point out another method of doing the same:

但我想指出另一种方法：

revenue.push_back({"string",map[i].second});

push_back() accepts a single parameter, so you could use "{}" to achieve this!

push_back() 接受单个参数，因此您可以使用“{}”来实现这一点！

回答by Dheeraj Kumar

Try using another temporary pair:

尝试使用另一个临时对：

pair<string,double> temp;
vector<pair<string,double>> revenue;

// Inside the loop
temp.first = "string";
temp.second = map[i].second;
revenue.push_back(temp);