C++ 学习笔记（9） RAII 在文件中的简单应用

出发点：及时释放文件资源

例子：ofstream 文件输出流 和 RAII 的结合

#include <bits/stdc++.h>
#define rep( i , j , n ) for ( int i = int(j) ; i < int(n) ; ++i )
#define dew( i , j , n ) for ( int i = int(n-1) ; i > int(j) ; --i )
#define _PATH __FILE__ , __LINE__
typedef std::pair < int , int > P ;
using std::cin ;
using std::cout ;
using std::endl ;
using std::string ;
static std::atomic_int cnt{ 0 } ;

namespace YHL {
	// 模拟  boost::nocopyable 不可复制
	class Noncopyable {
	public:
		Noncopyable() = default ;
		~Noncopyable() = default ;
	private:
		Noncopyable(const Noncopyable&) = delete ;
		Noncopyable& operator=(const Noncopyable&) = delete ;
	} ;
}

class myFile : private YHL::Noncopyable {
private:
	// 文件输出流
	std::ofstream fileHandle ;
	myFile(const myFile&) = delete ;
	myFile& operator=(const myFile&) = delete ;
public:
	myFile() = default ;
	explicit myFile(const char* fileName) {
			fileHandle.open(fileName, std::ios::app) ;
			if ( !fileHandle.good() )
				throw std::runtime_error("文件打开失败");
		}
	~myFile() { 
		// RAII 局部对象自动调用析构函数关闭文件输出流
		if( fileHandle.is_open() ) {
			fileHandle.close() ; 
			cout << "析构函数关闭文件输出流" << endl ;
		}
	}

	bool writeFile(const char *str) {
		try {
			if ( !fileHandle.is_open() )
				throw std::runtime_error("文件尚未打开") ;
		} catch ( std::exception &e ) {
			cout << e.what() << endl ; 
			cout << "fileName  :  " ;
		    string fileName ;
		    cin >> fileName ;
		    fileHandle.open(fileName, std::ios::app) ;
		}
		try {
			if ( !fileHandle.is_open() )
				throw std::runtime_error("文件写入失败") ;
		} catch ( std::exception &e ) {
			cout << e.what() << endl ; return false ;
		}
		fileHandle << str ;
		return true ;
	}

	bool writeFile(const char *fileName, const char *str) {
		if( fileHandle.is_open() ) 
			fileHandle.close() ;
		fileHandle.open(fileName, std::ios::app) ;
		try {
			if ( !fileHandle.is_open() )
				throw std::runtime_error("文件写入失败") ;
		} catch ( std::exception &e ) {
			cout << e.what() << endl ; return false ;
		}
		fileHandle << str ;
		return true ;
	}
} ;


int main () {
	myFile example("RAII(1).txt") ;
	example.writeFile("I love You forever") ;	

	example.writeFile("RAII(2).txt", "In the rest of my life") ;

	myFile example2 ;
	example2.writeFile("if you would like to") ;
	return 0 ;
}