C++ 保留 std::vector<> 的前 N 个元素并删除其余元素
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Keeping the first N elements of a std::vector<> and removing the rest
提问by Brett
I have a std::vector<int>variable in my C++application. The size of the vector is determined at runtime, but is typically about 1000.
std::vector<int>我的C++应用程序中有一个变量。向量的大小在运行时确定，但通常约为1000。
I have sorted this vector (which works well), and after sorting, I would like to keep only the first 50elements.
我已经对这个向量进行了排序（效果很好），排序后，我只想保留第一个50元素。
I have tried:
我试过了：
kpts.erase(kpts.begin() + 50, kpts.end());
where kptsis my vector, and the performance is horrible! Presumably because of the way eraseoperates.
kpts我的矢量在哪里，性能太糟糕了！大概是因为erase操作方式。
Is there a way to only keep the first 50elements of a vector?It seems like it should be obvious, but I can't find a way to do this.
有没有办法只保留50向量的第一个元素？看起来应该很明显，但我找不到办法做到这一点。
回答by Moritz
Yes, you can use std::vector::resize, which just truncates if the length of the vector is greater than n.
是的，您可以使用std::vector::resize，如果向量的长度大于 n，它只会截断。
See here: http://www.cplusplus.com/reference/vector/vector/resize/
见这里：http: //www.cplusplus.com/reference/vector/vector/resize/
std::vector<int> myvector;
for (int i=1;i<1000;i++) myvector.push_back(i);
myvector.resize(50);
// myvector will contain values 1..50
