C++缺省参数的具体使用

#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;
}

//a.h
void TestFunc(int a = 10);
//a.cpp
void TestFunc(int a = 20)
{}

    void f(bool b=false)
      {
            if (b)
            {
                  file://code of open file
            }
            else
            {
                  file://code of close file
            }
      }

      void Open()
      {
                  file://code of open file
      }
      void Close()
      {
                  file://code of close file
      }

      class CString
      {
      private:
            char * pcData;
      public:
            CString(char * pc=NULL);
      };
      CString::CString(char * pc)
      {
            if (pc==NULL)
            {
                  pcData=new char[1];
                  //...
            }
            else
            {
                  pcData=new char[strlen(pc)+1];
                  //...
            }
      }

      class CString
      {
      private:
            char * pcData;
      public:
            CString();
            CString(char * pc);
      };
      CString::CString()
      {
            pcData=new char[1];
            //...
      }
      CString::CString(char * pc)
      {
            pcData=new char[strlen(pc)+1];
            //...
      }

      class CPoint
      {
      public:
            int x;
            int y;
            CPoint(int x=0,int y=0)
            {
                  this->x=x;
                  this->y=y;
            }
      };

      CPoint pnt1;
      CPoint pnt2(100,100);
      CPoint pnt3(100);      file://[1]

      class CPoint
      {
      public:
            int x;
            int y;
            CPoint()
            {
                  x=0;
                  y=0;
            }
            CPoint(int x,int y)
            {
                  this->x=x;
                  this->y=y;
            }
      };

      void f(int a,int b=0)
      {
      }
      void f(int a)
      {
      }

      class CBase
      {
      public:
            virtual void f(int i=0)
            {
                  cout<<"in CBase "<<i<<endl;
            }
      };
      class CDerive : public CBase
      {
      public:
            virtual void f(int i=100)
            {
                  cout<<"in CDerive "<<i<<endl;
            }
      };
      CDerive d;
      CBase * pb=&d;
      pb->f();      file://[2]