C++/二维向量的大小
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C++/Size of a 2d vector
提问by pandoragami
How do I find the size of a 2 dimensional vector? So far I have the following code which doesn't compile.
如何找到二维向量的大小？到目前为止，我有以下无法编译的代码。
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector < vector <int> > v2d;
for (int x = 0; x < 3; x++)
{
for (int y = 0; y < 5; y++)
{
v2d.push_back(vector <int> ());
v2d[x].push_back(y);
}
}
cout<<v2d[0].size()<<endl;
cout<<v2d[0][0].size()<<endl;
return 0;
}
回答by Shamim Hafiz
To get the size of v2d, simply use v2d.size(). For size of each vector inside v2d, use v2d[k].size().
要获得v2d的大小，只需使用v2d.size()。对于v2d中每个向量的大小，请使用v2d[k].size()。
Note: for getting the whole sizeof v2d, sum up the size of each individual vector, as each vector has its own size.
注：为获得全尺寸的v2d，总结每个个体向量的大小，因为每个矢量都有自己的大小。
回答by moinudin
You had some errors in your code, which I've fixed and commented on below.
您的代码中有一些错误，我已修复并在下面进行了评论。
vector < vector <int> > v2d;
for (int x = 0; x < 3; x++)
{
// Move push_back() into the outer loop so it's called once per
// iteration of the x-loop
v2d.push_back(vector <int> ());
for (int y = 0; y < 5; y++)
{
v2d[x].push_back(y);
}
}
cout<<v2d.size()<<endl; // Remove the [0]
cout<<v2d[0].size()<<endl; // Remove one [0]
v2d.size()returns the number of vectors in the 2D vector. v2d[x].size()returns the number of vectors in "row" x. If you know the vector is rectangular (all "rows" are of the same size), you can get the total size with v2d.size() * v2d[0].size(). Otherwise you need to loop through the "rows":
v2d.size()返回二维向量中的向量数。v2d[x].size()返回 "row" 中的向量数x。如果您知道向量是矩形的（所有“行”的大小相同），则可以使用v2d.size() * v2d[0].size(). 否则，您需要遍历“行”：
int size = 0;
for (int i = 0; i < v2d.size(); i++)
size += v2d[i].size();
As a change, you can also use iterators:
作为更改，您还可以使用迭代器：
int size = 0;
for (vector<vector<int> >::const_iterator it = v2d.begin(); it != v2d.end(); ++it)
size += it->size();
回答by Puppy
The vector<vector<int>>does not have a whole size, because each vector within it has an independent size. You need to sum the size of all contained vectors.
在vector<vector<int>>没有一个全尺寸的，因为在它的每个向量具有独立的尺寸。您需要对所有包含的向量的大小求和。
int size = 0;
for(int i = 0; i < v2d.size(); i++)
size += v2d[i].size();
回答by yanshengjia
int size_row = v2d.size();
int size_col = v2d[0].size();
