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  1. #include <cstring>
  2. #include <iostream>
  3.  
  4. using namespace std;
  5.  
  6. // Test for copy-ellision
  7.  
  8. // A is old school class with pass-by-const-ref operator=
  9. class A
  10. {
  11.   public:
  12.  
  13.   static int n,d,c;
  14.  
  15.   A() : ptr(0),size(0) {}
  16.   A(size_t sz) : size(sz)
  17.   {
  18.     n++;
  19.     ptr = new float[sz];
  20.   }
  21.  
  22.   A(A const& src)
  23.   {
  24.     size = src.size;
  25.     n++;
  26.     ptr = new float[size];
  27.     c++;
  28.     memcpy(ptr,src.ptr,sizeof(float)*size);
  29.   }
  30.  
  31.   A& operator=(A const& src)
  32.   {
  33.     if(this != &src)
  34.     {
  35.       size = src.size;
  36.       d++;
  37.       if(ptr) delete[] ptr;
  38.       n++;
  39.       ptr = new float[size];
  40.       c++;
  41.       memcpy(ptr,src.ptr,sizeof(float)*size);
  42.     }
  43.  
  44.     return *this;
  45.   }
  46.  
  47.   void operator()() { cout << "non-const call" << endl; }
  48.  
  49.   ~A()
  50.   {
  51.     d++;
  52.     if(ptr) delete[] ptr;
  53.     ptr = 0;
  54.   }
  55.  
  56.   private:
  57.   float*  ptr;
  58.   int     size;
  59. };
  60.  
  61. int A::n = 0;
  62. int A::d = 0;
  63. int A::c = 0;
  64.  
  65. // B is new school class with pass-by-value operator=
  66. class B
  67. {
  68.   public:
  69.  
  70.   static int n,d,c;
  71.  
  72.   B() : ptr(0),size(0) {}
  73.   B(size_t sz) : size(sz)
  74.   {
  75.     n++;
  76.     ptr = new float[sz];
  77.   }
  78.  
  79.   B(B const& src)
  80.   {
  81.     size = src.size;
  82.     n++;
  83.     ptr = new float[size];
  84.     c++;
  85.     memcpy(ptr,src.ptr,sizeof(float)*size);
  86.   }
  87.  
  88.   B& operator=(B src)
  89.   {
  90.     swap(src);
  91.     return *this;
  92.   }
  93.  
  94.   void swap(B& src)
  95.   {
  96.     std::swap(size,src.size);
  97.     std::swap(ptr,src.ptr);
  98.   }
  99.  
  100.   void operator()() { cout << "non-const call" << endl; }
  101.  
  102.   ~B()
  103.   {
  104.     d++;
  105.     if(ptr) delete[] ptr;
  106.     ptr = 0;
  107.   }
  108.  
  109.   private:
  110.   float*  ptr;
  111.   int     size;
  112. };
  113.  
  114. int B::n = 0;
  115. int B::d = 0;
  116. int B::c = 0;
  117.  
  118. A sort( A const& names)
  119. {
  120.   A ret = names;
  121.   ret();
  122.   return ret;
  123. }
  124.  
  125. B sort( B names)
  126. {
  127.   names();
  128.   return names;
  129. }
  130.  
  131. int main()
  132. {
  133.   cout << "gcc " << __GNUC__  <<  "." <<      __GNUC_MINOR__<< endl;
  134.   {
  135.     A a;
  136.  
  137.     a = A(5);
  138.  
  139.     A c;
  140.     c = sort(A(7));
  141.   }
  142.  
  143.   cout << "A new : " << A::n << endl;
  144.   cout << "A delete : " << A::d << endl;
  145.   cout << "A copy : " << A::c << endl;
  146.   cout << endl;
  147.  
  148.   {
  149.     B a;
  150.  
  151.     a = B(8);
  152.  
  153.     B c;
  154.     c = sort(B(9));
  155.   }
  156.  
  157.   cout << "B new : " << B::n << endl;
  158.   cout << "B delete : " << B::d << endl;
  159.   cout << "B copy : " << B::c << endl;
  160.   cout << endl;
  161.  
  162. }
  163.  
Success #stdin #stdout 0.02s 2816KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
gcc 4.3
non-const call
A new : 5
A delete : 7
A copy : 3

non-const call
B new : 3
B delete : 5
B copy : 1
https://ideone.com/QYYZKl
language:
C++ (gcc 8.3)
created:
13 years ago
visibility:
public

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