向量：：在C++ STL中的赋值（）-yiteyi-C++库

向量：：赋值（） 是一个C++中的STL，它通过替换旧元素来给向量元素赋值。如有必要，它还可以修改向量的大小。

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分配常量值的语法：

vectorname.assign(int size, int value)Parameters: size - number of values to be assignedvalue - value to be assigned to the vectorname

程序1：下面的程序展示了如何给向量赋值

CPP

                         // CPP program to demonstrate                       
                         // how to assign constant values to a vector                       
           
                         #include <bits/stdc++.h>                       
                         using                                     namespace                                     std;                       
           
                         int                                     main()                       
                         {                       
                                                 vector<                                     int                                     > v;                       
                                                 v.assign(7, 100);                       
           
                                                 cout <<                                     "Size of first: "                       
                                                 <<                                     int                                     (v.size()) <<                                     ''                                     ;                       
           
                                                 cout <<                                     "Elements are"                                     ;                       
                                                 for                                     (                                     int                                     i = 0; i < v.size(); i++)                       
                                                 cout << v[i] << endl;                       
                                                 return                                     0;                       
                         }                       

输出

Size of first: 7Elements are100100100100100100100

从数组或列表中赋值的语法：

vectorname.assign(arr, arr + size)Parameters: arr - the array which is to be assigned to a vectorsize - number of elements from the beginning which has to be assigned.

程序2：下面的程序展示了如何从数组或列表中赋值

CPP

                         // CPP program to demonstrate                       
                         // how to assign values to a vector                       
                         // from a list                       
           
                         #include <bits/stdc++.h>                       
                         using                                     namespace                                     std;                       
           
                         int                                     main()                       
                         {                       
                                                 vector<                                     int                                     > v1;                       
                                                 int                                     a[] = { 1, 2, 3 };                       
           
                                                 // assign first 2 values                       
                                                 v1.assign(a, a + 2);                       
           
                                                 cout <<                                     "Elements of vector1 are"                                     ;                       
                                                 for                                     (                                     int                                     i = 0; i < v1.size(); i++)                       
                                                 cout << v1[i] <<                                     " "                                     ;                       
           
                                                 vector<                                     int                                     > v2;                       
                                                 // assign first 3 values                       
                                                 v2.assign(a, a + 3);                       
           
                                                 cout <<                                     "Elements of vector2 are"                                     ;                       
                                                 for                                     (                                     int                                     i = 0; i < v2.size(); i++)                       
                                                 cout << v2[i] <<                                     " "                                     ;                       
           
                                                 return                                     0;                       
                         }                       

输出

Elements of vector1 are1 2 Elements of vector2 are1 2 3

用于修改向量值的语法

vectorname.assign(InputIterator first, InputIterator last) Parameters: first - Input iterator to the initial position range.last - Input iterator to the final position range.

程序3：下面的程序显示了如何修改向量

CPP

                         // CPP program to demonstrate                       
                         // how to modify vector size                       
           
                         #include <bits/stdc++.h>                       
                         using                                     namespace                                     std;                       
           
                         int                                     main()                       
                         {                       
                                                 vector<                                     int                                     > v;                       
                                                 v.assign(7, 100);                       
           
                                                 cout <<                                     "Size of first: "                                     <<                                     int                                     (v.size()) <<                                     ''                                     ;                       
           
                                                 cout <<                                     "Elements are"                                     ;                       
                                                 for                                     (                                     int                                     i = 0; i < v.size(); i++)                       
                                                 cout << v[i] << endl;                       
           
                                                 // modify the elements                       
                                                 v.assign(v.begin(), v.begin() + 3);                       
           
                                                 cout <<                                     "Modified VectorElements are"                                     ;                       
                                                 for                                     (                                     int                                     i = 0; i < v.size(); i++)                       
                                                 cout << v[i] << endl;                       
                                                 return                                     0;                       
                         }                       

输出

Size of first: 7Elements are100100100100100100100Modified VectorElements are100100100

使用初始值设定项列表赋值的语法：

vectorname.assign((initializer_list)Parameter: initializer_list

程序4：下面的程序显示了如何使用初始值设定项列表分配向量。

C++

                         #include <iostream>                       
                         #include <vector>                       
                         using                                     namespace                                     std;                       
                         int                                     main()                       
                         {                       
                                                 vector<                                     int                                     > v;                       
                                   
                                                 // Initialize v with an initialization list                       
                                                 v.assign({ 1, 2, 3 });                       
                                                 cout <<                                     "The list is:"                                     << endl;                       
                                                 for                                     (                                     auto                                     i = v.begin(); i != v.end(); i++)                       
                                                 {                       
                                                 // Printing 1 2 3 as output                       
                                                 cout << *i <<                                     " "                                     ;                       
                                                 }                       
                                                 return                                     0;                       
                         }                       

输出

The list is:1 2 3

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