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  1. /*****************************************************************
  2. Name : 陣列長度的外置(集中定義)
  3. Date : 2017/04/27
  4. By   : CharlotteHonG
  5. Final: 2017/04/27
  6. *****************************************************************/
  7. #include <iostream>
  8. using namespace std;
  9.  
  10. // const可以直接初始化
  11. class const_init{
  12. public:
  13.     const_init(int len=10):len(len){
  14.         cout << "len=" << len << endl;
  15.     }
  16. private:
  17.     const int len;
  18. };
  19.  
  20. // C11 支持類內定義
  21. // 委託結構定義
  22. struct Array_size{
  23.     static const int len = 10;
  24. };
  25. class defstru{
  26. public:
  27.     defstru(){
  28.         cout << "len=" << sizeof(arr)/sizeof(arr[0]) << endl;
  29.     }
  30. private:
  31.     int arr[Array_size::len];
  32. };
  33. // 直接定義在類別內也可
  34. class defin{
  35. public:
  36.     defin(){
  37.         cout << "len=" << sizeof(arr)/sizeof(arr[0]) << endl;
  38.     }
  39. private:
  40.     static const int len = 10;
  41.     int arr[Array_size::len];
  42. };
  43.  
  44.  
  45. // 不支持類內定義可以拉出來定義
  46. struct Array_size2{
  47.     static const int len;
  48. };
  49. const int Array_size2::len=10;
  50.  
  51.  
  52. // 拉出來定義要是再不行還可以用 enmu
  53. class defenmu{
  54. public:
  55.     defenmu(){
  56.         cout << "len=" << sizeof(arr)/sizeof(arr[0]) << endl;
  57.     }
  58. private:
  59.     enum{Array_size=10};
  60.     int arr[Array_size];
  61. };
  62.  
  63.  
  64. // 還有一個手段 constexpr
  65. struct Array_size4{
  66.     static constexpr size_t len1(){
  67.         return 10;
  68.     }
  69. } size;
  70. class deffunc{
  71. public:
  72.     deffunc(){
  73.         cout << "len=" << sizeof(arr)/sizeof(arr[0]) << endl;
  74.     }
  75. private:
  76.     int arr[Array_size4::len1()];
  77.     int arr2[size.len1()];
  78. };
  79. //================================================================
  80. int main(int argc, char const *argv[]){
  81.     defstru a;
  82.     defin b;
  83.     defenmu c;
  84.     const_init d;
  85.     deffunc e;
  86.     return 0;
  87. }
  88. //================================================================
  89.  
Success #stdin #stdout 0s 15240KB
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Standard input is empty
stdout
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len=10
len=10
len=10
len=10
len=10
https://ideone.com/QC4nfM
陣列長度的外置(集中定義)
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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