45 lines
1.1 KiB
C++
45 lines
1.1 KiB
C++
//
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// Created by light on 19-12-16.
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//
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#include <iostream>
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#include <queue>
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#include <vector>
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using namespace std;
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class Obj1 {
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public:
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Obj1() { cout << "Obj1()\n"; }
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Obj1(const Obj1 &) { cout << "Obj1(const Obj1&)\n"; }
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Obj1(Obj1 &&) { cout << "Obj1(Obj1&&)\n"; }
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};
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class Obj2 {
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public:
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Obj2() { cout << "Obj2()\n"; }
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Obj2(const Obj2 &) { cout << "Obj2(const Obj2&)\n"; }
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Obj2(Obj2 &&) noexcept { cout << "Obj2(Obj2&&)\n"; }
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};
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int main() {
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vector<int> v;
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int nums = 20;
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for (int i = 0; i < nums; ++i) {
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v.push_back(i + 1);
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cout << "v_size: " << v.size() << "\t v_capacity: " << v.capacity() << endl;
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}
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// 头两个在已有空间上成功构造。第三个时发现空间不足，系统会请求更大的空间，大小由实现决定（比如两倍）。
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// 有了足够的空间后，就会在新空间的第三个的位置构造（第三个obj1），成功之后再把头两个拷贝或移动过来。
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vector<Obj1> v1;
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// v1.reserve(2);
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v1.emplace_back();
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v1.emplace_back();
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v1.emplace_back();
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v1.emplace_back();
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vector<Obj2> v2;
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v2.reserve(2);
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v2.emplace_back();
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v2.emplace_back();
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v2.emplace_back();
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} |