1.detach使用时分析

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使用detach时，子线程一定不要传入指针

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#include<iostream>
#include<thread>
using namespace std;

void my_print(const int& num1,const char* str) {
	cout << num1 << " " << str << endl;
}
//主进程结束后，才开始对子进程中的值进行拷贝。但是主进程释放了str1，子进程接收时会出现问题。
int main() {
	int num1 = 1;
	char str1[] = "hello,world!";
	thread obj1(my_print,num1,str1);
	obj1.detach();
	cout << "主进程结束运行" << endl;
	return 0;
}

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如果采用临时类对象作为参数，传入到thread中，thread会调用拷贝构造函数，对传入变量进行拷贝，然后再为自线程所使用。

下面的代码采用引用来接收类对象，如果不采用引用的话，系统还会再构造一次对象，这样会出现3次构造，浪费时间。

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#include<iostream>
#include<thread>
using namespace std;

class son_thread {
public:
	int m_a;
	son_thread(int a):m_a(a) {
		cout << "构造函数的调用" << endl;
	}
	~son_thread() {
		cout << "析构函数的调用" << endl;
	}
};

void my_print(const int a,const son_thread& st) {
	cout << a << " " << st.m_a << endl;
}
int main() {
	int num1 = 1;
	int num2 = 10;
	thread obj1(my_print, num1,son_thread(num2));
	obj1.detach();
	cout << "主进程结束运行" << endl;
	return 0;
}

2. 临时对象

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1.如果对象采用隐式转换，将会在子线程中进行构造对象；

2.如果对象采用显示转换，将会在主线程中进行构造对象，并会调用拷贝构造函数。

this_thread::get_id()---->显示线程的id号

注意：

当采用隐式传递时，是在子线程进行类对象构造，但是此时主线程已经销毁，主线程内的局部变量已经释放，此时操作会有危险。

当采用显式构造是，首先会在主线程构造出一个临时对象，然后在主线程中进行复制拷贝构造，随后在主线程内将临时对象进行释放。

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#include<iostream>
#include<thread>
using namespace std;
class son_thread {
public:
	int m_a;
	son_thread(int a) :m_a(a) {
		cout << "son_thread构造函数调用" << this_thread::get_id() << endl;
	}
	son_thread(const son_thread& base):m_a(base.m_a) {
		cout << "son_thread拷贝构造函数的调用" << this_thread::get_id()<< endl;
	}
	~son_thread() {
		cout << "son_thread析构函数调用" << this_thread::get_id()<< endl;
	}
};
void my_print(const son_thread& base) {
	cout << base.m_a << " my_print调用" << this_thread::get_id()<< endl;
}
int main() {
	int temp_a = 1;
	cout << "主线程的id:" << this_thread::get_id() << endl;
	//thread obj1(my_print, temp_a);
	thread obj1(my_print, son_thread(temp_a));
	obj1.join();
	cout << "主线程调用完毕:" << this_thread::get_id() << endl;

	return 0;
}

 3.传递智能指针、类对象

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因为在传递类对象是，子线程会调用拷贝构造函数，因此子线程修改类对象成员变量时，并不会修改主线程内的对象成员变量。

此时我们可以用：std::ref（）函数

在传入unique_ptr智能指针时，可以使用std::move()对智能指针进行更改。

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#include<iostream>
#include<thread>
using namespace std;
class son_thread {
public:
	int m_a;
	son_thread(int a) :m_a(a) {
		cout << "son_thread构造函数调用" << this_thread::get_id() << endl;
	}
	son_thread(const son_thread& base) :m_a(base.m_a) {
		cout << "son_thread拷贝构造函数的调用" << this_thread::get_id() << endl;
	}
	~son_thread() {
		cout << "son_thread析构函数调用" << this_thread::get_id() << endl;
	}
};
void my_print(unique_ptr<int>temp_pt) {
	cout << *temp_pt << " my_print调用" << this_thread::get_id() << endl;
}
int main() {
	int temp_a = 1;
	cout << "主线程的id:" << this_thread::get_id() << endl;
	unique_ptr<int>u_pt(new int (100));
	thread obj1(my_print, std::move(u_pt));
	obj1.join();
	cout << "主线程调用完毕:" << this_thread::get_id() << endl;

	return 0;
}

4.将类函数的函数作为入口函数 

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#include<iostream>
#include<thread>

using namespace std;
class son_thread {
public:
	int m_a;
	son_thread(int a) :m_a(a) {
		cout << "son_thread构造函数调用" << this_thread::get_id() << endl;
	}
	son_thread(const son_thread& base) :m_a(base.m_a) {
		cout << "son_thread拷贝构造函数的调用" << this_thread::get_id() << endl;
	}
	~son_thread() {
		cout << "son_thread析构函数调用" << this_thread::get_id() << endl;
	}
	void my_print(const int a ) {
		cout << a << " 类内函数的调用" << endl;
	}
};

int main() {
	cout << "主线程的id:" << this_thread::get_id() << endl;
	son_thread s1(10);
	thread obj1(&son_thread::my_print, s1, 100);
	obj1.join();
	cout << "主线程调用完毕:" << this_thread::get_id() << endl;
	return 0;
}