C++ 将元素替换为向量的特定位置
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Replace an element into a specific position of a vector
提问by daiyue
I want to replace an element into a specific position of a vector, can I just use an assignment:
我想将一个元素替换到一个向量的特定位置，我可以只使用一个赋值：
// vec1 and 2 have the same length & filled in somehow
vec1;
vec2;
vec1[i] = vec2[i] // insert vec2[i] at position i of vec1
or I have to use insert():
或者我必须使用插入（）：
vector<sometype>::iterator iterator = vec1.begin();
vec1.insert(iterator+(i+1), vec2[i]);
回答by Armen Tsirunyan
vec1[i] = vec2[i]
will set the value of vec1[i]to the value of vec2[i]. Nothing is inserted. Your second approach is almost correct. Instead of +i+1you need just +i
将 的值设置vec1[i]为 的值vec2[i]。没有插入任何内容。你的第二种方法几乎是正确的。而不是+i+1你只需要+i
v1.insert(v1.begin()+i, v2[i])
回答by Pantelis Sopasakis
You can do that using at. You can try out the following simple example:
您可以使用at做到这一点。您可以尝试以下简单示例：
const size_t N = 20;
std::vector<int> vec(N);
try {
vec.at(N - 1) = 7;
} catch (std::out_of_range ex) {
std::cout << ex.what() << std::endl;
}
assert(vec.at(N - 1) == 7);
Notice that method atreturns an allocator_type::reference, which is that case is a int&. Using atis equivalent to assigning values like vec[i]=....
请注意，该方法at返回 an allocator_type::reference，即情况为 a int&。使用at等效于分配像vec[i]=....
There is a difference between atand insertas it can be understood with the following example:
at和insert之间有区别，可以通过以下示例来理解：
const size_t N = 8;
std::vector<int> vec(N);
for (size_t i = 0; i<5; i++){
vec[i] = i + 1;
}
vec.insert(vec.begin()+2, 10);
If we now print out vecwe will get:
如果我们现在打印出来，vec我们将得到：
1 2 10 3 4 5 0 0 0
If, instead, we did vec.at(2) = 10, or vec[2]=10, we would get
相反，如果我们做了vec.at(2) = 10，或者vec[2]=10，我们会得到
1 2 10 4 5 0 0 0
回答by virlan2004
See an example here: http://www.cplusplus.com/reference/stl/vector/insert/eg.:
在此处查看示例：http: //www.cplusplus.com/reference/stl/vector/insert/例如：
...
vector::iterator iterator1;
iterator1= vec1.begin();
vec1.insert ( iterator1+i , vec2[i] );
// This means that at position "i" from the beginning it will insert the value from vec2 from position i
Your first approach was replacing the values from vec1[i] with the values from vec2[i]
您的第一种方法是将 vec1[i] 中的值替换为 vec2[i] 中的值
