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c++11 stl 学习之 shared_ptr

2024-08-07 15:07:43   222人阅读

shared_ptr
智能指针 shared_ptr 的声明初始化方式
由于指针指针使用explicit参数 必须显示声明初始化
shared_ptr<string> pNico = new string("nico"); // ERROR
shared_ptr<string> pNico{new string("nico")}; // OK

也可以使用make_shared()
shared_ptr<string> pNico = make_shared<string>("nico");
shared_ptr<string> pJutta = make_shared<string>("jutta");

智能指针一旦声明
就不能再次分配 除非使用reset()
shared_ptr<string> pNico4;
pNico4 = new string("nico");
//ERROR: no assignment for ordinary pointers
pNico4.reset(new string("nico")); // OK

shared_ptr的使用方式与实际指针使用类似 基本没什么区别

示例 sharedPtrTest1()

//=======================================
对于shared_ptr中的参数 可以指定 删除器 Deleter
示例 sharedPtrTest2()

#include <iostream>#include <string>#include <vector>#include <memory>#include <fstream> //for ofstream#include <cstdio> //for remove()using namespace std;void sharedPtrTest1(){	shared_ptr<string> pNico(new string("nico"));	shared_ptr<string> pJutta(new string("jutta"));	(*pNico)[0] = ‘N‘;	pJutta->replace(0, 1, "J");	vector<shared_ptr<string>> whoMadeCoffee;	whoMadeCoffee.push_back(pJutta);	whoMadeCoffee.push_back(pJutta);	whoMadeCoffee.push_back(pNico);	whoMadeCoffee.push_back(pJutta);	whoMadeCoffee.push_back(pNico);	for (auto ptr : whoMadeCoffee) {		cout << *ptr << " ";	}	cout << endl;	// overwrite a name again	*pNico = "Nicolai";	// print all elements again	for (auto ptr : whoMadeCoffee) {		cout << *ptr << " ";	}	cout << endl;	// print some internal data	cout << "use_count: " << whoMadeCoffee[0].use_count() << endl;}class FileDeleter{private:	std::string filename;public:	FileDeleter(const std::string& fn)		: filename(fn) {	}	void operator () (std::ofstream* fp) {		fp->close(); //close.file		std::remove(filename.c_str()); //delete file		cout << "delete file finish" << endl;	}};void sharedPtrTest2(){	shared_ptr<std::ofstream> fp(new std::ofstream("tmpfile.txt"),		FileDeleter("tmpfile.txt"));}int _tmain(int argc, _TCHAR* argv[]){	sharedPtrTest1();	sharedPtrTest2();	return 0;}

　　

 

c++11 stl 学习之 shared_ptr


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