C++ 简单的正则

C++ 简单的正则

本人初学C++ 如有遗漏和错误，望斧正！
本文只是简单的介绍一下C++对txt文件的简单读和写
希望大家喜欢
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C++ 简单的正则

在Windows下读取txt文件时往往需要从中提取一些内容，比如GPS模块返回日志的txt文件中经纬度的提取

$GNRMC,071550.000,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,A*7F

因此为了方便我们可以利用简单的正则将其输出

GPS文件内容名称为GPSTest.txt

$GNRMC,071549.000,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*77
$GNRMC,071549.200,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*75
$GNRMC,071549.400,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*73
$GNRMC,071549.600,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*71
$GNRMC,071549.800,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*7F
$GNRMC,071550.000,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*7F
$GNRMC,071550.200,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*7D
$GNRMC,071550.400,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*7B
$GNRMC,071550.600,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*79
$GNRMC,071550.800,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*77
$GNRMC,071551.000,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*7E
$GNRMC,071551.200,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*7C
$GNRMC,071551.400,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*7A
$GNRMC,071551.600,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*78

相关应用链接->GPS项目

1. 正则库

#include<regex>

​ 其中拥有正则运算相关的函数

2. regex_match 演示

string str = "Hello_2018";
smatch result;//regex专用储存
regex pattern("(.{5})_(\\d{4})");	//匹配5个任意单字符 + 下划线 + 4个数字

if (regex_match(str, result, pattern))
{
	cout << result[0] << endl;		//完整匹配结果，Hello_2018
	cout << result[1] << endl;		//第一组匹配的数据，Hello
	cout << result[2] << endl;		//第二组匹配的数据，2018
	cout<<"结果显示形式2"<<endl;
	cout<< result.str() << endl;	//完整结果，Hello_2018
	cout<< result.str(1) << endl;	//第一组匹配的数据，Hello
	cout << result.str(2) << endl;	//第二组匹配的数据，2018
}

//遍历结果
for (int i = 0; i < result.size(); ++i)
{
	cout << result[i] << endl;
}

2. regex_search 演示

string str = "$GNRMC,071550.000,A,2325.0070,N,11637.7624,E,000.0,000.0,170920,,,A*7F";
smatch result;
regex pattern("\\d{4}.\\d{4}");	//匹配四个数字

//迭代器声明
string::const_iterator iterStart = str.begin();
string::const_iterator iterEnd = str.end();
string temp;
while (regex_search(iterStart, iterEnd, result, pattern))
{
	temp = result[0];
	cout << temp << " ";
	iterStart = result[0].second;	//更新搜索起始位置,搜索剩下的字符串
}

输出结果：2018 2017

其中const_interator是函数迭代器->函数迭代器

3. regex_match 与 regex_search 的差别

cout << regex_match("123", regex("\\d")) << endl;		//结果为0
cout << regex_search("123", regex("\\d")) << endl;		//结果为1

4. match vs search

match()函数只检测RE是不是在string的开始位置匹配，
也就是说match()只有在0位置匹配成功的话才有返回，
如果不是开始位置匹配成功的话，match()就返回none.

search()会扫描整个string查找匹配；
search()可以不从0位置开始匹配，这就是和match()的区别。

5.实践

#include<iostream>
#include<fstream>
#include<cstdlib>
#include<regex>
#include<string>

using namespace std;

int main()
{


	ifstream inFile; // 读写相关可见链接
	inFile.open("GPSTest.txt"); 

	if (!inFile.is_open())
	{
		cout << "Fail to open!"<< endl;
		exit(EXIT_FAILURE);
	}

	string Inf;
	regex pattern1("\\d{4}.\\d{4},\\w");
	regex pattern2("\\d{5}.\\d{4},\\w");
	smatch result1;
	smatch result2;

	while (getline(inFile, Inf))//getline(input,string(content)) 之所以不用 inFile.get(ch) 和 inFile.getline(ch,number)是因为其储存的是char和char数组
	{
		string::const_iterator interStart = Inf.begin();
		string::const_iterator interEnd = Inf.end();
		while (regex_search(interStart, interEnd,result1,pattern1))
		{
			while (regex_search(interStart, interEnd, result2, pattern2))
			{
				cout <<"经度："<< result1[0] << '\t' << "纬度："<< result2[0] << endl; // result为结果其中的编号为优先比配到的
				
				interStart = interEnd; //*******函数迭代的头尾令其头部为空跳出这个while和下一个while循环
			}
		}
	}

	inFile.close();
	system("pause");
	return 0 ;
}

C++文件的简单读取
结果如图所示