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  1. /*****************************************************************
  2. Name : 重載下標符號 const 函式
  3. Date : 2017/02/20
  4. By   : CharlotteHonG
  5. Final: 2017/02/20
  6. *****************************************************************/
  7. #include <iostream>
  8. #include <vector>
  9. #include <numeric>
  10.  
  11. using namespace std;
  12.  
  13. class Arr{
  14. public:
  15.     // 建構子
  16.     Arr(int len): arr(len){
  17.         iota(arr.begin(),arr.end(),1);
  18.     }
  19.     // 重載下標符號
  20.     int & operator[](size_t idx){
  21.     	cout << "**Non-Const**" << endl;
  22.         return const_cast<int&>(static_cast<const Arr&>(*this)[idx]);
  23.     }
  24.     const int & operator[](size_t idx) const{
  25.         cout << "**Const**" << endl;
  26.         return arr[idx];
  27.     }
  28. private:
  29.     vector<int> arr;
  30. };
  31.  
  32. void pri(const int & num){
  33.     cout << "num=" << num << endl;
  34. }
  35. int main(){
  36.     const Arr ca(5);
  37.     pri(ca[0]);
  38.     Arr a(5);
  39.     pri(a[0]);
  40.     return 0;
  41. }
Success #stdin #stdout 0s 15240KB
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Standard input is empty
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**Const**
num=1
**Non-Const**
**Const**
num=1
https://ideone.com/ZyqPgc
重載下標符號 const 函式
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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