C++ 如何推回向量的向量？
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how to pushback on a vector of vectors?
提问by Masterminder
I am taking 20 lines of input. I want to separate the contents of each line by a space and put it into a vector of vectors. How do I make a vector of vectors? I am having have struggles pushing it back...
我正在输入 20 行。我想用空格分隔每一行的内容并将其放入向量的向量中。如何制作向量的向量？我很难把它推回去......
My input file:
我的输入文件：
Mary had a little lamb
lalala up the hill
the sun is up
The vector should look like something like this.
矢量应该看起来像这样。
ROW 0: {"Mary","had", "a","little","lamb"}
ROW 1: {"lalala","up","the","hill"}
This is my code....
这是我的代码....
string line;
vector <vector<string> > big;
string buf;
for (int i = 0; i < 20; i++){
getline(cin, line);
stringstream ss(line);
while (ss >> buf){
(big[i]).push_back(buf);
}
}
回答by paddy
The code is right, but your vector has zero elements in it so you cannot access big[i].
代码是正确的，但是您的向量中包含零个元素，因此您无法访问big[i].
Set the vector size before the loop, either in the constructor or like this:
在循环之前设置向量大小，在构造函数中或像这样：
big.resize(ruleNum);
Alternatively you can push an empty vector in each loop step:
或者，您可以在每个循环步骤中推送一个空向量：
big.push_back( vector<string>() );
You don't need the parentheses around big[i]either.
你也不需要括号big[i]。
回答by juanchopanza
Yo could start with a vector of size ruleNum
你可以从一个大小的向量开始 ruleNum
vector <vector<string> > big(ruleNum);
This will hold ruleNumempty vector<string>elements. You can then push back elements into each one, as you are currently doing in the example you posted.
这将保存ruleNum空vector<string>元素。然后，您可以将元素推回每个元素，就像您目前在发布的示例中所做的那样。
回答by taocp
You can do the following:
您可以执行以下操作：
string line;
vector <vector<string> > big; //BTW:In C++11, you can skip the space between > and >
string currStr;
for (int i = 0; i < ruleNum; i++){
getline(cin, line);
stringstream ss(line);
vector<string> buf;
while (ss >> currStr){
buf.push_back(buf);
}
big.push_back(buf);
}
回答by moovon
vector<vector<string> > v;
to push_back into vectors of vectors, we will push_back strings in the internal vector and push_back the internal vector in to the external vector.
要将push_back 推入向量的向量中，我们将push_back 内部向量中的字符串并将内部向量push_back 推入外部向量。
Simple code to show its implementation:
显示其实现的简单代码：
vector<vector<string> > v;
vector<string> s;
s.push_back("Stack");
s.push_back("oveflow");`
s.push_back("c++");
// now push_back the entire vector "s" into "v"
v.push_back(s);
