STL中vector的assign()函数用法

参考：

1. https://blog.csdn.net/qq_45893475/article/details/120250105
2. https://blog.csdn.net/doubleintfloat/article/details/52280481?spm=1001.2101.3001.6650.1&utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-1.no_search_link&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-1.no_search_link

一、assign函数原型：

void assign(const_iterator first,const_iterator last);
void assign(size_type n,const T& x = T());

功能：

1. 第一个相当于拷贝函数，把first到last的值赋值给调用者，注意区间的闭合，即：将区间 [first,last) 的元素赋值到当前的 vector 容器中；
2. 第二个是把n个x赋值给调用者，即：赋 n 个值为 x 的元素到 vector 容器中，并且清除掉 vector 容器中以前的内容。

二、示例：

#include <vector>
#include <iostream>
using namespace std;

int main() {
 	vector<int> v1, v2, v3;
 	vector<int>::iterator iter;
 	v1.push_back(10);
 	v1.push_back(20);
 	v1.push_back(30);
 	v2.push_back(1);
 	v2.push_back(2);
    
 	cout << "v1 = " ;
 	for (iter = v1.begin(); iter != v1.end(); iter++)
  		cout << *iter << " ";
 	cout << endl;
    
	cout << "v2 = ";
 	for (iter = v2.begin(); iter != v2.end(); iter++)
  		cout << *iter << " ";
 	cout << endl;
	
    /*v2 = v1;
 	cout << "v2 = ";
 	for (iter = v2.begin(); iter != v2.end(); iter++)
  		cout << *iter << " ";
 	cout << endl;*/
 	
    v2.assign(v1.begin(), v1.end());
    cout << "v2 = ";
 	for (iter = v2.begin(); iter != v2.end(); iter++)
  		cout << *iter << " ";
 	cout << endl;
 	
    v3.assign(7, 3) ;
 	cout << "v3 = ";
 	for (iter = v3.begin(); iter != v3.end(); iter++)
  		cout << *iter << " ";
 	cout << endl;
    
 	return 0;
}

#include<iostream>
#include<vector>
using namespace std;

int main()
{
	vector<int>ls;
	vector<int>ls1;

	for(int i=0; i<20; ++i)
	{
		ls.push_back(i);
	}
	vector<int>::iterator lr = ls.begin();
	for(; lr != ls.end(); ++lr)
	{
		cout<<*lr<<" ";
	}
	cout<<endl;
	ls1.assign(ls.begin(),ls.begin()+9);

	for(lr = ls1.begin(); lr !=ls1.end(); ++lr)
	{
		cout<<*lr<<" ";
	}
	cout<<endl;
	
	ls.assign(10,7);
	for(lr = ls.begin(); lr !=ls.end(); ++lr)
	{
		cout<<*lr<<" ";
	}
	cout<<endl;
	return 0;
}

输出结果：
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
0 1 2 3 4 5 6 7 8
7 7 7 7 7 7 7 7 7 7