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  1. // vector::reserve
  2.     #include <iostream>
  3.     #include <vector>
  4.  
  5.     int main ()
  6.     {
  7.         std::vector<int>::size_type sz;
  8.  
  9.         std::vector<int> foo;
  10.         sz = foo.capacity();
  11.         std::cout << "making foo grow:\n";
  12.         for (int i=0; i<100; ++i) {
  13.             foo.push_back(i);
  14.             if (sz!=foo.capacity()) {
  15.                 sz = foo.capacity();
  16.                 std::cout << "capacity changed: " << sz << ", " << i << "\n";
  17.             }
  18.         }
  19.  
  20.         std::vector<int> bar;
  21.         sz = bar.capacity();
  22.         bar.reserve(100);   // this is the only difference with foo above
  23.         std::cout << "making bar grow:\n";
  24.         for (int i=0; i<100; ++i) {
  25.             bar.push_back(i);
  26.             if (sz!=bar.capacity()) {
  27.                 sz = bar.capacity();
  28.                 std::cout << "capacity changed: " << sz << '\n';
  29.             }
  30.         }
  31.  
  32.         return 0;
  33.     }
Success #stdin #stdout 0.01s 2812KB
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stdin
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Standard input is empty
stdout
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making foo grow:
capacity changed: 1, 0
capacity changed: 2, 1
capacity changed: 4, 2
capacity changed: 8, 4
capacity changed: 16, 8
capacity changed: 32, 16
capacity changed: 64, 32
capacity changed: 128, 64
making bar grow:
capacity changed: 100
https://ideone.com/Tl0rZc
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
public

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