【C++】函数和指针

最近在看C++ primer plus，感觉函数与指针这一章难点比较多，记写笔记，加强理解.

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(); //函数名调用
double x = (*pf)(); //指针调用
double x = pf(); //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,)<<":"<<*(*p1)(av,)<<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,)<<":"<<*p2(av,)<<endl;

4.  函数指针数组

const double *(*pa[]) (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[](av,); //call by pointer as if it were a function name
const double *py = (*pa[])(av,); //正常调用

//得到函数返回指针指向的值
double x = *pa[](av,);
double x = *(*pa[])(av,);

5. 指向指针数组的指针

指针数组和数组指针的区别

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

指向数组的指针

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

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

 **&pa = *pa = pa[]

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[] = {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,)<<":"<<*(*p1)(av,)<<endl;
     cout<<p2(av,)<<":"<<*p2(av,)<<endl;

     //pa an array of pointers
     //auto doesn't work with list initialization
     const double *(*pa[])(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 = ;i < ; i++)
         cout<<pa[i](av,)<<":"<<*pa[i](av,)<<endl;
     cout<<"\nUsing a pointer to a pointer to a function:\n";
     cout<<"Address Value\n";
     for(int i = ;i < ; i++)
         cout<<pb[i](av,)<<":"<<*pb[i](av,)<<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)[](av,)<<":"<<*(*pc)[](av,)<<endl;
     //hard way to declare pd
     const double *(*(*pd)[])(const double *,int) = &pa;
     //store return value in pdb
     const double *pdb = (*pd)[](av,);
     cout<<pdb<<":"<<*pdb<<endl;
     //alternative notation
     cout<<(*(pd)[])(av,)<<":"<<*(*(*pd)[])(av,)<<endl;
 }

 const double * f1(const double * ar, int n)
 {
 return ar;
 }
 const double * f2(const double ar[], int n)
 {
 return ar+;
 }
 const double * f3(const double ar[], int n)
 {
 return ar+;
 }