[英]How to initialize a list of std::vector's values in C++11?
I have a problem with the following code: 我有以下代码的问题:
const std::vector < std::string > arr1 = { "a", "b", "c" };
const std::vector < std::string > arr2 = { "e", "f", "g" };
const std::vector < std::string > globaArr = { arr1, arr2 }; // error
I need to initialize globalArr with values: "a", "b", "c", "e", "f", "g" (in one dimension). 我需要用值来初始化globalArr:“a”,“b”,“c”,“e”,“f”,“g”(在一个维度上)。 I don't need to have two-dimensional array. 我不需要二维数组。 What do I do wrong? 我做错了什么?
I can do something like this: 我可以这样做:
globalArr.push_back( arr1 ); // with the for loop inserting each value of arr1
globalArr.push_back( arr2 );
but here the globalArr is not const anymore :) I need the same type for all three vectors. 但是这里的globalArr不再是const :)我需要所有三个向量的相同类型。
You could implement a function that just sums them. 你可以实现一个只对它们求和的函数。 Say, operator+
: 说, operator+
:
template <class T>
std::vector<T> operator+(std::vector<T> const& lhs,
std::vector<T> const& rhs)
{
auto tmp(lhs);
tmp.insert(tmp.end(), rhs.begin(), rhs.end());
return tmp;
}
And then just use that: 然后使用它:
const std::vector<std::string> arr1 = { "a", "b", "c" };
const std::vector<std::string> arr2 = { "e", "f", "g" };
const std::vector<std::string> sum = arr1 + arr2;
The function could be named anything, I just picked +
for simplicity. 该函数可以命名为任何东西,我只是为了简单而选择+
。
In the upcoming Ranges TS , it will be possible to write the solution by @Barry as 在即将推出的Ranges TS中 ,可以用@Barry编写解决方案
#include <range/v3/all.hpp>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
int main()
{
using namespace ranges;
const std::vector<std::string> arr1 = { "a", "b", "c" };
const std::vector<std::string> arr2 = { "e", "f", "g" };
const auto sum = view::concat(arr1, arr2) | to_vector;
std::copy(sum.begin(), sum.end(), std::ostream_iterator<std::string>(std::cout, ","));
}
If all you're trying to do is simply put the elements of arr1
and arr2
into globaArr
, why not use a for loop? 如果你要做的只是简单地将arr1
和arr2
的元素放入globaArr
,为什么不使用for循环呢?
Example: 例:
for ( int i = 0; i < (int)arr1.size(); i++ ) {
globaArr.push_back(arr1.at(i));
}
for ( int i = 0; i < (int)arr2.size(); i++ ) {
globaArr.push_back(arr1.at(i));
}
Better yet, just write a function that takes in globaArr
and a vector that you want to add to globaArr
from. 更好的是,只需编写一个函数,它接受globaArr
和你想要添加到globaArr
的向量。 Put the for loop in the function and call the function twice. 将for循环放在函数中并调用该函数两次。 A little more work, but probably cleaner code. 多一点工作,但可能更清晰的代码。
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