C++ 如何获取字符串向量中某个元素的位置，将其用作整数向量中的索引？
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How to get position of a certain element in strings vector, to use it as an index in ints vector?
提问by Nour
I am trying to get the index of an element in a vector of strings, to use it as an index in another vector of inttype, is this possible ?
我正在尝试获取向量中元素的索引strings，以将其用作另一个int类型向量中的索引，这可能吗？
Example:
例子：
vector <string> Names;
vector <int> Numbers;
...
// condition to check whether the name exists or not
if((find(Names.begin(), Names.end(), old_name_)) != Names.end())
{ // if yes
cout <<"Enter the new name."<< endl;
cin >> name;
replace(Names.begin(), Names.end(), old_name_, name);
}
Now I want to get the position of old_namein the Namesvector, to use it in accessing certain element in Numbersvector. So that I can say:
现在，我想要得到的位置old_name的Names矢量，在访问某些元素使用它Numbers载体。这样我就可以说：
Numbers[position] = 3 ; // or whatever value assigned here.
I tried using:
我尝试使用：
vector <string> :: const_iterator pos;
pos = (find(Names.begin(), Names.end(), old_name_))
Numbers[pos] = 3;
but obviously this doesn't work since posis of type string !
但显然这不起作用，因为它pos是字符串类型！
回答by dasblinkenlight
To get a position of an element in a vector knowing an iterator pointing to the element, simply subtract v.begin()from the iterator:
要在知道指向元素的迭代器的情况下获取元素在向量中的位置，只需v.begin()从迭代器中减去：
ptrdiff_t pos = find(Names.begin(), Names.end(), old_name_) - Names.begin();
Now you need to check posagainst Names.size()to see if it is out of bounds or not:
现在，你需要检查pos对Names.size()，看它是否是界限或不出来：
if(pos >= Names.size()) {
//old_name_ not found
}
vector iterators behave in ways similar to array pointers; most of what you know about pointer arithmetic can be applied to vector iterators as well.
向量迭代器的行为方式类似于数组指针；您对指针算术的了解大部分也可以应用于向量迭代器。
Starting with C++11 you can use std::distancein place of subtraction for both iterators and pointers:
从 C++11 开始，您可以使用std::distance迭代器和指针代替减法：
ptrdiff_t pos = distance(Names.begin(), find(Names.begin(), Names.end(), old_name_));
回答by juanchopanza
If you want an index, you can use std::findin combination with std::distance.
如果需要索引，可以std::find与std::distance.
auto it = std::find(Names.begin(), Names.end(), old_name_);
if (it == Names.end())
{
// name not in vector
} else
{
auto index = std::distance(Names.begin(), it);
}
回答by javer
I am a beginner so here is a beginners answer. The if in the for loop gives i which can then be used however needed such as Numbers[i] in another vector. Most is fluff for examples sake, the for/if really says it all.
我是初学者，所以这里是初学者的答案。for 循环中的 if 给出了 i ，然后可以使用它，但需要使用另一个向量中的 Numbers[i] 。例如，大多数都是绒毛，for/if 真的说明了一切。
int main(){
vector<string>names{"Sara", "Harold", "Frank", "Taylor", "Sasha", "Seymore"};
string req_name;
cout<<"Enter search name: "<<'\n';
cin>>req_name;
for(int i=0; i<=names.size()-1; ++i) {
if(names[i]==req_name){
cout<<"The index number for "<<req_name<<" is "<<i<<'\n';
return 0;
}
else if(names[i]!=req_name && i==names.size()-1) {
cout<<"That name is not an element in this vector"<<'\n';
} else {
continue;
}
}
