1. C++常用的遍历方法

1. C++常用的遍历方法

遍历：指的是集合中每个元素只访问一次。常见的方法有一下六种。

下面以字符串遍历与数组（向量）遍历为例

【字符串遍历】

string str("XDU");
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1. 传统Cfor写法

   for(size_t i = 0; i < str.size(); i++){
   	cout << str[i] << endl;
   }
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   size_t:

   ​ 一个基本的无符号整型的C/C++类型，它是sizeof操作返回的结果，该类型的大小可选择。因此，它可以存储在理论上可能的任何类型的数组的大小。

   size_t相当于unsigned int 是无符号整型

   typedef unsigned int size_t

2. 迭代器for写法

   for(string::iterator it = str.begin(); it!=str.end(); it++){
   	cout << *it << endl;
   }
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3. STLfor_each写法

   for(char c : str){
       cout << c <<endl;
   }
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4. C++11迭代器写法

   for(string::iterator it = begin(str); it != end(str); it++){
       cout << *it << endl;
   }
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   或者

   for(auto it = begin(str); it != end(str); it++){
       cout<< *it << endl;
   }
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5. C++11 for loop scope 写法

   for(char c : str){
       cout << c << endl;
   }
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   或者

   for(auto c : str){
       cout << c <<endl;
   }
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6. C++11 STL for_each与lamdba表达式

   //使用for_each遍历需要引用头文件#include<algorithm>
   for_each(begin(str),end(str),[](char c){cout << c << endl;});
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【C++代码】

#include<algorithm>
int main() {
	string str = "XDU";
	//遍历1
	for (size_t i = 0; i < str.size(); i++) {
		cout << str[i] << endl;
	}
	cout << "--------------------------------" << endl;
	//遍历2
	for (string::iterator it = str.begin(); it != str.end(); it++) {
		cout << *it << endl;
	}
	cout << "--------------------------------" << endl;
	//遍历3
	for (char c : str)
	{
		cout << c << endl;
	}
	cout << "--------------------------------" << endl;
	//遍历4：写法一
	for (string :: iterator it = begin(str); it != end(str); it++) {
		cout << *it << endl;
	}
	cout << "--------------------------------" << endl;
	//遍历4：写法二：用auto代替string::iterator 类型
	for (auto it = begin(str); it != end(str); it++) {
		cout << *it << endl;
	}
	cout << "--------------------------------" << endl;
	//遍历5：写法一
	for (char c : str) {
		cout << c << endl;
	}
	cout << "--------------------------------" << endl;
	//遍历5：写法二用auto代替char类型
	for (auto c : str) {
		cout << c << endl;
	}
	cout << "--------------------------------" << endl;
	//遍历6:for_each
	for_each(begin(str), end(str), [](char c) { cout << c << endl; });
	system("pause");
	return 0;
}
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【结果】

【向量遍历】

vector<char> vec;
vec.push_back('X');
vec.push_back('D');
vec.push_back('U');
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1. C语言写法

   for(size_t i = 0; i < vec.size(); i++){
       cout << vec[i] << endl;
   }
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2. 迭代器

   for(vector<char>::iterator it = vec.begin(); it != vec.end(); it++){
   	cout << *it << endl;
   }
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3. STL for_each写法

   void print(char n){
       cout << n <<endl; 
   }
   for_each(vec.begin(), vec.end(), print);
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4. C++11迭代器写法

   for(vector<int>::iterator it = begin(vec); it != end(vec); it++){
   	cout << *it << endl;
   }
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   或者

   for(auto it = begin(vec); it != end(vec); it++){
       cout << *it << endl;
   }
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5. C++11 for新语法写法

   for(int n : vec){
       cout << n << endl;
   }
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   或者

   for(auto n : vec){
       cout << n << endl;
   }
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6. C++11STL for_each与lamdba表达式

   for_each(begin(vec),end(vec),[](int n){cout << n << endl;});
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【c++代码】

int main(){
	Scout << "向量遍历" << endl;
	vector<char> vec;
	vec.push_back('M');
	vec.push_back('B');
	vec.push_back('Y');
	//向量遍历1：
	for (size_t i = 0; i < vec.size(); i++) {
		cout << vec[i] << endl;
	}
	cout << "--------------------------------" << endl;
	//向量遍历2：迭代法写法一
	for (vector<char>::iterator it = vec.begin(); it != vec.end(); it++) {
		cout << *it << endl;
	}
	cout << "--------------------------------" << endl;
	//向量遍历2：迭代法写法二
	for (auto it = vec.begin(); it != vec.end(); it++) {
		cout << *it << endl;
	}
	cout << "--------------------------------" << endl;
	//向量遍历3：STL for_each
	for_each(vec.begin(), vec.end(),print);
	cout << "--------------------------------" << endl;
	//向量遍历4：C++迭代器写法
	for (vector<char>::iterator it = begin(vec); it != end(vec); it++) {
		cout << *it << endl;
	}
	//或
	for (auto it = begin(vec); it != end(vec); it++) {
		cout << *it << endl;
	}
	cout << "--------------------------------" << endl;
	//向量遍历 forC++新语法
	for (auto n : vec) {
		cout << n << endl;
	}
	cout << "--------------------------------" << endl;
	//C++11STLfor_each与lamdba表达式
	for_each(begin(vec), end(vec), [](char n) {cout << n << endl; });
	cout << "--------------------------------" << endl;
	system("pause");
	return 0;
	return 0;
}
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【结果】