C++获取数组的长度（用模板可以实现）

#include<iostream>
using namespace  std;

int getArrLen1(int *&a){//error

	return sizeof(a)/sizeof(a[0]);

}
int getArrLen2(int *a){

	return sizeof(a)/sizeof(a[0]);

}
template<typename T>
int getArrayLength1(T a){
	return sizeof(a)/sizeof(a[0]);
}
/**
正确的获取数组长度的函数（虽然是模板）
*/
template<typename T>
int getArrayLength2(T &a){
	return sizeof(a)/sizeof(a[0]);
}

int main(){
	int *p = new int[200];
	int size = *(p-4);
	cout << size << endl;
	size = *(p-3);
	cout << size << endl;
	size = *(p-2);
	cout << size << endl;
	size = *(p-1);
	cout << size << endl;
	

	int a[100];
	cout << "a address:" << a << endl;
	cout << "&a address:" << &a << endl;
	/*
	C:UsersjackzDesktopcodescpp>g++ getArrayLength.cpp
	getArrayLength.cpp: In function "int main()":
	getArrayLength.cpp:39:22: error: invalid initialization of non-const reference o
	f type "int*&" from an rvalue of type "int*"
	 cout << getArrLen1(a) << endl;
                      ^
	getArrayLength.cpp:4:5: note:   initializing argument 1 of "int getArrLen1(int*&
	)"
	int getArrLen1(int *&a){
		^

	*/	
	//cout << getArrLen1(a) << endl;//error
	//cout << "&&a address:" << &&a << endl;//error
	cout << getArrLen2(a) << endl;
	cout << getArrayLength1(a) << endl;//1
	cout << getArrayLength2(a) << endl;//100
	return 0;
	
}

C:UsersjackzDesktopcodescpp>g++ getArrayLength.cpp

C:UsersjackzDesktopcodescpp>a
0
0
1633043277
134352027
a address:0x28fd78
&a address:0x28fd78
1
1
100