说明

引用

引用不是对象，他只是给已经存在的对象所起的另一个名字，因此你不能引用一个引用，只能引用已存在的对象。 可以把引用看作约束化的指针，它同样可以被传递，间接访问，但是更加安全，因为它只是对象的“小名”，就比如鲁迅和周树人的关系。引用虽然也地址相关，但只是内存块的别名。

指针

指针就很熟悉了，它本身就是一个变量，void*和T*类型的指针可以存储T类型对象的地址。因为是一个变量，可以被赋值。

const引用

const 声明定义的量是只读的常量，因此可以引用，但是引用也不能改变它只读的性质，同样的，不可以用普通引用去引用常量（或者常量的引用，其实也是常量）。

有一种值得讨论的情况： 就是形如：

double i = 1.0; const double &S = 3.14*i*i; //（1）

这时候编译器会有一个暂时变量用于保存3.14*i*i的计算结果 计作tmp那么语句（1）其实等效为：

const double tmp = 3.14*i*i; const double &S = tmp;

并且这里的tmp也是只读的

定义

引用

int val1 = 42, val2 = 666; int &val1_ref = val1, other_val = val2; //val1_ref是ref1的引用，other_val是另一个无关的int型的变量，只是被val2初始化了

指针

int i = 42; int *iptr = &i; // (*iptr)--;

const引用

double i = 1.0; const double &r = i; //r是i的只读引用 const double &C = 2*3.14*r; //C是中间变量的常量引用 const double &S = 3.14*i*i; //同上，即使i变化S、C的值都不会变化

区别

definition

#include<iostream> using namespace std; int main() { int i = 42; //reference int &i_ref = i; //pointer int *iptr = &i; //const reference const int &i_conref = i; cout << "i = " << i << ", i_ref = " << i_ref <<endl; i_ref--; cout << "now i = " << i << ", i_ref = " << i_ref <<endl; (*iptr)--; cout << "now *iptr = " << *iptr << ", i_con-ref = " << i_conref <<endl; return 0; }

compare

#include<iostream> using namespace std; int main() { double i = 1.0; const double &r = i; double &ii = i; const double &C = r*2; const double &S = i*i*2; cout << "r = " <<r<< " rr = " <<ii<<" C = "<<C<<" S = "<<S<< endl; i++;cout << "r = " <<r<< " rr = " <<ii<<" C = "<<C<<" S = "<<S<< endl; i++;cout << "r = " <<r<< " rr = " <<ii<<" C = "<<C<<" S = "<<S<< endl; i++;cout << "r = " <<r<< " rr = " <<ii<<" C = "<<C<<" S = "<<S<< endl; //point of reference double const *tptr = &r; cout << "point of i via reference r "<< (*tptr) << endl; //point of tmpvarible double const *sao = &C; cout << "point of C "<< (*sao) << endl; //(*sao)++; cout << "point of C "<< (*sao) << endl; // read-only //reference of point double *iptr = &i; double *&iref = iptr; (*iref)++; cout << "now *tptr = " << *iptr << " pref = " << *iref << endl; return 0; }

output as fellow:

pi@pi:~/script/cpp$ ./out r = 1 rr = 1 C = 2 S = 2 r = 2 rr = 2 C = 2 S = 2 r = 3 rr = 3 C = 2 S = 2 r = 4 rr = 4 C = 2 S = 2 point of i via reference r 4 point of C 2 now *tptr = 5 pref = 5

参数传递

#include<iostream> using namespace std; void swap1(int *a, int *b) { (*a) = (*a) ^ (*b); (*b) = (*a) ^ (*b); (*a) = (*a) ^ (*b); } void swap2(int &a, int &b) { a = a ^ b; b = a ^ b; a = a ^ b; } int main() { int a = 1 , b = 2; cout << "1 a = " <<a<<" b = "<<b<<endl; swap1(&a,&b); cout << "2 a = " <<a<<" b = "<<b<<endl; swap2(a,b); cout << "3 a = " <<a<<" b = "<<b<<endl; return 0; }

reference

[1] c++ Primer [2] http://www.cnblogs.com/Mr-xu/archive/2012/08/07/2626973.html [3] http://blog.csdn.net/listening_music/article/details/6921608 [4] http://www.cnblogs.com/dolphin0520/archive/2011/04/03/2004869.html