c++函数指针

 

1.声明函数指针

　　声明指向某种数据类型的指针时，必须指定指针指向的类型。同样，声明指向函数的指针时，也必须指定指针指向的函数类型。这意味着声明应指定函数的返回类型一级函数的特征标（参数列表）。也就是说，声明应像函数原型那样指出有关函数的信息。
　　例如：

　　　　

double pam(int); //prototype

　　则正确的指针类型声明如下：

double (*pf) (int);//pf points to a function that takes one int argument and that return type double

　　这与pam()声明类似，这是将pam替换为（*pf）。由于pam是函数，因此（*pf）也是函数。而如果（*pf）是函数，则pf就是函数指针。

　　为了提供正确的运算符优先级，必须在声明中是用括号将*pf括起。括号的优先级比*运算符高，因此*pf(int)意味着pf()是一个返回指针的函数，而（*pf）(int)意味着pf是一个指向函数的指针。

2.使用指针来调用函数

pf = pam;                         //pf指向函数pam()
double x = pam(4);           //用函数名调用函数pam()
double y = (*pf)(4);          //用函数指针pf调用函数pam()

3.函数指针示例1

 

#include <iostream>

double betsy(int);
double pam(int);

void estimate(int lines, double (*pt) (int));


int main()
{
    using namespace std;
    int code;
    cout << "How many lines of code do you need? ";
    cin >> code;
    cout<<"Here's Betsy's estimate\n";
    estimate(code,betsy);
    cout << "Here's Pam's estimate:\n";
    estimate(code, pam);
    cin.get();
    cin.get();
    return 0;
}

double betsy(int lns)
{
    return 0.05 * lns;
}

double pam(int lns)
{
    return 0.03 * lns + 0.0004 * lns * lns;
}

void estimate(int lines, double(*pf)(int))
{
    using namespace std;
    cout << lines<<" lines will take ";
    cout << (*pf)(lines) << " hour(s)\n";
}

执行结果

函数指针实例2

#include <iostream>
double add(double x, double y)
{
    return x + y;
}

double sub(double x, double y)
{
    return x-y;
}

double div(double x, double y)
{
    return x/y;
}
double calculate(double,double,double(*add)(double,double));

int main()
{
    using namespace std;
    double x, y; 
    double(*pf[3])(double,double) = {add, sub, div};
    while(cin>>x>>y)
    {
        cout<<"sum = "<<(*pf[0])(x,y)<<endl;
        cout<<"sub = "<<(*pf[1])(x,y)<<endl;
        cout<<"div = "<<(*pf[2])(x,y)<<endl;
        cout<<"sum = "<<calculate(x,y,pf[0])<<endl;
        cout<<"sub = "<<calculate(x,y,pf[1])<<endl;
        cout<<"div = "<<calculate(x,y,pf[2])<<endl;
    }

    cin.get();
    cin.get();
    return 0;
    
}

double calculate(double x,double y,double(*padd)(double,double))
{
    return (*padd)(x,y);
}

 

深入函数指针示例

#include <iostream>
 
 
 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};
 
     const double * (*p1)(const double *,int) = f1;
     auto p2 = 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;
 
     const double *(*pa[3])(const double *, int) = {f1, f2, f3};
     
     auto pb = 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 << "Using 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;
     }
 
     cout << "Using a pointer to an array of function:\n";
     cout << " Address Value\n";
 
     auto pc = &pa;
 
     cout << (*pc)[0](av, 3) << ": "<< *(*pc)[0](av, 3) <<endl;
     const double *(*(*pd)[3])(const double *, int) = &pa;
     const double *pdb = (*pd)[1](av,3);
     cout<<pdb << ": "<< *pdb << endl;
     cout<< (*(*pd)[2])(av,3) << ": " << *(*(*pd)[2])(av,3)<<endl;
     cin.get();
     cin.get();
     return 0;
 }
 
 const double * f1(const double ar[], int n)
 {
     return ar;
 }
 const double * f2(const double ar[], int)
 {
     return ar + 1;
 }
 const double * f3(const double * ar, int)
 {
     return ar + 2;
 }

 

执行结果