C/C++的const總介紹

const.c

簡單的介紹C中const的用法  1 int main()  2 {  3   const char ch = 'a';  4   const int a[5] = {1, 2, 3, 4, 5};    5   int b[5] = {6, 7, 8, 9, 10};    6   int c[4][4] = {{11,12,13,14},{15,16,17,18},{19,20,21,22},{23,24,25,26}};  7   const int *p1 = a;                8   int *const p2 = a;                9   const int * const p3 = b; 10   const int ** const p4 = c; 11 12   ch = 'b';//error: ch is const, can't be modified 13   p1 = &a[2]; //ok, *p1 is const, p1 is not 14   *p1 = 5;//error, *p1 is const, a[2] is const 15   *(p1 + 2) = 1; //error, *p1 is const 16   p1 = &b[2];//ok 17   *p1 = 4;//error, *p1 is const 18   p2 = &b[4];//error, p2 is const 19   p2++;//error, p2 is const 20   *p2 = 10;//error, *p2 is not const, p2 is, but a[0] is const 21   p2 = &a[5];//error, p2 is const 22   p3 = &b[1];//error, p3 is const 23   *p3 = 3;//error, *p3 is const 24   p4 = b;//error, p4 is const 25   *(*p4+2) = 10; //error, **p4 is const 26   *p4 = b; 27   printf("%d", **p4); //6, *p4 = b 28   **p4 = 10;//error, **p4 is const 29    30   return 0; 31 } 32 --------------------------------------------------------------------------------------

const.cpp

簡單的介紹C++中const的用法  1 /*  2  * =====================================================================================  3  *  4  *       Filename:  const.cpp  5  *  6  *    Description:    7  *  8  *        Version:  1.0  9  *        Created:  06/04/2009 09:01:15 PM 10  *       Revision:  none 11  *       Compiler:  gcc 12  * 13  *         Author:  YOUR NAME (), 14  *        Company:   15  * 16  * ===================================================================================== 17  */ 18 #include <stdio.h> 19 #include <stdlib.h> 20 class Ball { 21   static const int ID = 100;//initialize only once, can't modify anymore 22   //const int ID2; //can't modify it anymore, and initialize 23   char *name; 24   int money; 25   mutable int bonus; 26   public: 27   Ball(){ 28     name = (char *)malloc(8); 29     name[0] = 'y'; 30     name[1] = 's'; 31   } 32   int setID(int id){ 33     //ID = 200;//error, ID is const 34   } 35   void showID(){ 36     printf("ID:%d\n", ID); 37   } 38   const char* getConstName() { return name; } 39   char* getName() { return name; } 40   int getMoney() const { 41     //money++;//error, function is const, can't modify any its class member 42     bonus++;//ok, it is mutable, can be used in const function 43     return money+bonus; } 44 }; 45 int main() 46 { 47   Ball b = Ball(); 48   b.showID(); 49   printf("name:%s\n", b.getName()); 50   b.getName()[2]='l'; 51   printf("name:%s\n", b.getName()); 52   //b.getConstName()[2]='l';//error, return const can't modify 53   printf("money:%d\n", b.getMoney()); 54 55   return 0; 56 } 57 --------------------------------------------------------------------------------------

const.cpp

簡單的介紹C++中const templates的iterator用法,還有其中content為const時如何去掉const來呼叫  1 #include <iostream>  2 #include <vector>  3 #include <map>  4 #include <string>  5  6 using namespace std;  7  8 class Symbolic{  9     public: 10         Symbolic(int v, string e){ 11             value_ = v; 12             expr_ = e; 13         } 14 15         void Print(){ 16             cout<<"value:"<<value_<<", "<<expr_<<endl; 17         } 18          19         void constPrint() const{ 20             cout<<"value:"<<value_<<", "<<expr_<<endl; 21         } 22     private: 23         int value_; 24         string expr_; 25 }; 26 27 void vectorPrint(const vector<const Symbolic *>& v) 28 { 29     /* const_iterator for const template iteration */ 30     vector<const Symbolic *>::const_iterator v_iter; 31     for(v_iter = v.begin(); v_iter != v.end(); v_iter++){ 32         /* make const member to be normal */ 33         const_cast<Symbolic *>(*v_iter)->Print(); 34         /* const class pointer only can call const function */ 35         (*v_iter)->constPrint(); 36     } 37 38 } 39 40 void mapPrint(const map<int, char>& m) 41 { 42     /* const_iterator for const template iteration */ 43     map<int, char>::const_iterator m_iter; 44     for(m_iter = m.begin(); m_iter != m.end(); m_iter++){ 45         cout<<"index:"<<m_iter->first<<" -> "<<m_iter->second<<endl; 46     } 47 } 48 49 int main() 50 { 51     vector<Symbolic *> constraints; 52 53     constraints.push_back(new Symbolic(1, "x")); 54     constraints.push_back(new Symbolic(2, "y")); 55     constraints.push_back(new Symbolic(3, "z")); 56 57     /* make its member to be const access */ 58     vector<const Symbolic*> cs(constraints.begin(), 59                            constraints.end()); 60     /* print its value and make it const to be sure that we don't modify it */ 61     vectorPrint(cs); 62 63 64     map<int, char> symb; 65 66     symb[1] = 'a'; 67     symb[2] = 'b'; 68     symb[3] = 'c'; 69 70     mapPrint(symb); 71 72     return 0; 73 }