C++ 使用 boost 分配初始化具有固定大小的向量的向量
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Initializing a vector of vectors having a fixed size with boost assign
提问by saloua
Having a vector of vector with a fixed size,
具有固定大小的向量向量，
vector<vector<int> > v(10);
I would like to initialize it so that it has in all elements a one dimensional vector with initialized value (for example 1).
我想初始化它，以便它在所有元素中都有一个带有初始化值的一维向量（例如 1）。
I have used Boost Assign as follows
我使用 Boost Assign 如下
v= repeat(10,list_of(list_of(1)));
and I've got a compilation error
我有一个编译错误
error: no matching function for call to ‘repeat(boost::assign_detail::generic_list<int>)'
Could you please tell me how to do that. Thanks in advance
你能告诉我怎么做吗。提前致谢
回答by juanchopanza
This doesn't use boost::assignbut does what you need:
这不使用，boost::assign但做你需要的：
vector<vector<int>> v(10, vector<int>(10,1));
This creates a vector containing 10 vectors of int, each containing 10 ints.
这将创建一个包含 10 个向量的向量int，每个向量包含 10个ints。
回答by hmjd
You don't need to use boostfor the required behaviour. The following creates a vectorof 10vector<int>s, with each vector<int>containing 10ints with a value of 1:
您不需要boost用于所需的行为。下面创建一个vector的10vector<int>S，其中每个vector<int>含有10int具有的值s 1：
std::vector<std::vector<int>> v(10, std::vector<int>(10, 1));
回答by moldovean
I will just try to explain it to those new to C++. A vector of verctors mathas the advantage that you can access its elements directly at almost no cost using the []operator..
我将尝试向那些刚接触 C++ 的人解释它。向量向量mat的优点是您可以使用[]运算符直接访问其元素，几乎没有成本。
int n(5), m(8);
vector<vector<int> > mat(n, vector<int>(m));
mat[0][0] =4; //direct assignment OR
for (int i=0;i<n;++i)
for(int j=0;j<m;++j){
mat[i][j] = rand() % 10;
}
Of course this is not the only way. And if you do not add or remove elements, one can also use the native containers mat[]which are nothing more than pointers. Here's my fav way, using C++:
当然，这不是唯一的方法。如果您不添加或删除元素，也可以使用mat[]仅是指针的本机容器。这是我最喜欢的方式，使用 C++：
int n(5), m(8);
int *matrix[n];
for(int i=0;i<n;++i){
matrix[i] = new int[m]; //allocating m elements of memory
for(int j=0;j<m;++j) matrix[i][j]= rand()%10;
}
This way, you don't have to use #include <vector>. Hopefully, it's clearer!
这样，您就不必使用#include <vector>. 希望它更清楚！
回答by Frank Hou
#include <vector>
#include <iostream>
using namespace std;
int main(){
int n; cin >> n;
vector<vector<int>> v(n);
//populate
for(int i=0; i<n; i++){
for(int j=0; j<n; j++){
int number; cin >> number;
v[i].push_back(number);
}
}
// display
for(int i=0; i<n; i++){
for(int j=0; j<n; j++){
cout << v[i][j] << " ";
}
cout << endl;
}
}
Input:
输入：
4
11 12 13 14
21 22 23 24
31 32 33 34
41 42 43 44
Output:
输出：
11 12 13 14
21 22 23 24
31 32 33 34
41 42 43 44
