vector的size(),capacity(),max_size()的用法和区别

最新推荐文章于 2024-08-16 14:37:02 发布

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本文介绍了C++标准库中Vector容器的几个关键属性：size()用于返回容器的大小；empty()用于判断容器是否为空；max_size()返回容器最大的可存储元素数量；capacity()则返回容器当前能够容纳的元素数量。通过实例演示了这些属性的应用。

在Vector容器中有以下几个关于大小的函数

方法	效果
size()	返回容器的大小
empty()	判断容器是否为空
max_size()	返回容器最大的可以存储的元素
capacity()	返回容器当前能够容纳的元素数量

#include <vector>
#include <string>
#include <iostream>
#include <algorithm>
#include <iterator>
using namespace std;
int main()  
{  
	vector<string> sentence;  
	sentence.reserve(5);  

	//append some elements  
	sentence.push_back("hello");  
	sentence.push_back("how");  
	sentence.push_back("are");  
	sentence.push_back("you");  
	sentence.push_back("?");  
	copy(sentence.begin(), sentence.end(), ostream_iterator<string>(cout, " "));  
	cout << endl;  

	//print "technical data"  
	cout << "max_size():" << sentence.max_size() << endl;  
	cout << "size():" << sentence.size() << endl;  
	cout << "capacity():" << sentence.capacity() << endl;  

	cout << "**************************" << endl;  

	//swap second and fourth element  
	swap(sentence[1], sentence[3]);   
	//insert element "always" before element "?"  
	sentence.insert(find(sentence.begin(), sentence.end(), "?"), "always");  
	//assign "!" to the last element  
	sentence.back() = "!";  
	copy(sentence.begin(), sentence.end(), ostream_iterator<string>(cout, " "));  
	cout << endl;  

	//print "technical data"  
	// return maximum possible length of sequence   
	//回容器的最大可以存储的元素个数，这是个极限，当容器扩展到这个最大值时就不能再自动增大  
	cout << "max_size():" << sentence.max_size() << endl;  
	// return length of sequence  
	cout << "size():" << sentence.size() << endl;  
	// return current length of allocated storage  
	cout << "capacity():" << sentence.capacity() << endl;  
	system("Pause");
	return 0;  
}