C++的缺省参数你了解嘛

#include<iOStream>
using namespace std;
void TestFunc(int a = 0)//参数缺省值
{
	cout << a << endl;
}
int main()
{
	TestFunc();//没有指定实参，使用缺省值
	TestFunc(10);//指定实参，使用实参
	return 0;
}

#include<iostream>
using namespace std;
namespace WD
{
	struct Stack
	{
		int* a;
		int size;
		int capacity;	
	};
}
using namespace WD;
void StackInit(struct Stack* ps)
{
	ps->a = NULL; 
	ps->capacity = 0;
	ps->size = 0;
}
void StackPush(struct Stack* ps, int x)
{
	if(ps->size == ps->capacity)
	{
		//ps->capacity *= 2;//err
		ps->capacity == 0 ? 4 : ps->capacity * 2;//这里就必须写一个三目
	}
}
void StackInitcpp1(struct Stack* ps, int defaultCP)
{
	ps->a = (int*)malloc(sizeof(int) * defaultCP);
	ps->capacity = 0;
	ps->size = defaultCP;
}
void StackInitCpp2(struct Stack* ps, int defaultCP = 4)//ok
{
	ps->a = (int*)malloc(sizeof(int) * defaultCP);
	ps->capacity = 0;
	ps->size = defaultCP;
}
int main()
{
	//假设明确知道这里至少需要100个数据到st1
	struct Stack st1; 
	StackInitCpp1(&st1, 100);
	//假设不知道st2里需要多少个数据 ———— 希望开小点
	struct Stack st2;  
	StackInitCpp2(&st1);//缺省
	return 0;
}

void TestFunc(int a = 10, int b = 20, int c = 30)
{
	cout << "a = " << a << endl;
	cout << "b = " << b << endl;
	cout << "c = " << c << endl;
	cout << endl;
}
int main()
{
	//非常灵活，
	TestFunc();
	TestFunc(1);
	TestFunc(1, 2);
	TestFunc(1, 2, 3);	
	//TestFunc(1, , 3);//err，注意它没办法实现b不传，只传a和b，也就是说编译器只能按照顺序传
	return 0;
}

//void TestFunc(int a, int b = 10,  int c = 20);//err，void TestFunc(int a, int b = 10,  int c = 20){cout << "a = " << a << endl;cout << "b = " << b << endl;cout << "c = " << c << endl;cout << endl;}int main(){//TestFunc();//err，至少得传一个，这是根据形参有几个非半缺省参数确定的TestFunc(1);TestFunc(1, 2);TestFunc(1, 2, 3);return 0;}//void TestFunc(int a, int b = 10,  int c = 20);//err，
void TestFunc(int a, int b = 10,  int c = 20)
{
	cout << "a = " << a << endl;
	cout << "b = " << b << endl;
	cout << "c = " << c << endl;
	cout << endl;
}
int main()
{
	//TestFunc();//err，至少得传一个，这是根据形参有几个非半缺省参数确定的
	TestFunc(1);
	TestFunc(1, 2);
	TestFunc(1, 2, 3);	
	return 0;
}

//a.hvoid TestFunc(int a = 10);//a.cppvoid TestFunc(int a = 20){}