C++函数与指针

From C++ Primer Plus: Chapter 7 Function:C++ Programming Modules

1. 如何声明函数指针？

和函数原型类似: 需要声明指针指向函数的返回值和参数列表

double pam(int); //参数为int 类型，返回值为double 类型的函数  double (*pf);(int)  //指向参数为int类型,返回值为double 类型的指针  pf = pam;   //函数名代表了函数的地址    double x = pam(4); //函数名调用  double x = (*pf)(4); //指针调用  double x = pf(4); //C++也允许将指针名当作函数名使用

2. C++ 11 自动类型推断

 const double * f1(const double *, int);   const double * (*p1)(const double *, int); //p1 poitns to f1   auto p2 = f1; //C++11 automatic type deduction,p2 points to f1 as well

3. 将指针名当作函数名使用

//前面函数为double *类型，cout第一部分返回double指针，第二部分返回double指针指向的值  cout<<(*p1)(av,3)<<":"<<*(*p1)(av,3)<<endl;  //和上面的cout一样只不过是使用函数指针名来调用函数  cout<<p2(av,3)<<":"<<*p2(av,3)<<endl;

4. 函数指针数组

const double *(*pa[3]) (const double *,int) = {f1,f2,f3}; //创建函数指针数组  //通过指针调用函数，得到返回的指针  const double *px = pa[0](av,3); //call by pointer as if it were a function name  const double *py = (*pa[0])(av,3); //正常调用    //得到函数返回指针指向的值  double x = *pa[0](av,3);  double x = *(*pa[0])(av,3);

5. 指向指针数组的指针

指针数组和数组指针的区别

*pd[3] //an array of 3 pointers  (*pd)[3] //a pointer to an array of three elements

指向数组的指针

1 auto pc = &pa; //&pa是整个数组的地址, pa是数组第一个元素首地址

2

3 const double * (*(*pd)[3])(const double *, int ) = &pa; //和第一个等价

4

5 **&pa = *pa = pa[0]

代码：

//arfupt.cpp -- an array of function pointers  #include<iostream>  //various notations,same signatures  const double *f1(const double ar[],int n);  const double *f2(const double [],int);  const double *f3(const double *,int);    int main()  {      using namespace std;      double av[3] = {1112.3,1542.6,2227.9};        //pointer to a function        const double *(*p1)(const double *,int) = f1;      auto p2 = f2;//C++ 11 utomatic  type deduction      //pre-C++11 can use the following code instead      //const double *(*p2)(const double *,int) = f2;      cout<<"Using pointers to functions:\n";      cout<<"Address Value\n";      cout<<(*p1)(av,3)<<":"<<*(*p1)(av,3)<<endl;      cout<<p2(av,3)<<":"<<*p2(av,3)<<endl;        //pa an array of pointers      //auto doesn't work with list initialization      const double *(*pa[3])(const double *,int) = {f1,f2,f3};      //pb a pointer to first element of pa      auto pb = pa;      // pre-C++11 can use the following code instead      // const double *(**pb)(const double *, int) = pa;      cout<<"\nUsing an array of pointers to functions:\n";      cout<<"Address Value\n";      for(int i = 0;i < 3; i++)          cout<<pa[i](av,3)<<":"<<*pa[i](av,3)<<endl;      cout<<"\nUsing a pointer to a pointer to a function:\n";      cout<<"Address Value\n";      for(int i = 0;i < 3; i++)          cout<<pb[i](av,3)<<":"<<*pb[i](av,3)<<endl;        //what about a pointer to an array of function pointers      cout<<"\nUsing pointers to an array of pointers:\n";      cout<<"Address Value\n";      //easy way to declare pc      auto pc = &pa;      // pre-C++11 can use the following code instead      // const double *(*(*pc)[3])(const double *, int) = &pa;      cout<<(*pc)[0](av,3)<<":"<<*(*pc)[0](av,3)<<endl;      //hard way to declare pd      const double *(*(*pd)[3])(const double *,int) = &pa;      //store return value in pdb      const double *pdb = (*pd)[1](av,3);      cout<<pdb<<":"<<*pdb<<endl;      //alternative notation      cout<<(*(pd)[2])(av,3)<<":"<<*(*(*pd)[2])(av,3)<<endl;  }    const double * f1(const double * ar, int n)  {  return ar;  }  const double * f2(const double ar[], int n)  {  return ar+1;  }  const double * f3(const double ar[], int n)  {  return ar+2;  }

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