Lesson 23 Temporary objects

One 、 Example

class test{
	private:
	int i;
	public:
	test(int j)
	{
		i = j;
	}
	test()
	{
		test(0); //  Here a temporary object is generated 
	}
	void printfi(void)
	{
		printf("%d", i);	
	};
}
int main(char* argc, char** argv)
{
	test t;
	t.printfi();
	return 0;
}

The output value of the above function is not 0, Why is that ？

A constructor is a special function , Calling the constructor directly will produce a temporary object , The declaration cycle of a temporary object is only the time of one statement , The scope of a temporary object is intended to be in a statement . The temporary object is C++ Notable gray areas in

The reason for the above phenomenon is the introduction of temporary objects .

• modern C++ The compiler does not affect the final execution result , We will try our best to reduce the generation of temporary objects

Two 、 Summary

• Calling the constructor directly will produce a temporary object

• Temporary objects are the bottleneck of performance , It's also bug One of the sources of

• modern C++ The compiler will try to avoid temporary objects

  The premise of avoiding is that it does not affect the execution result

• In the process of actual project development, it is necessary to avoid temporary objects