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69 lines
2.2 KiB
C++
69 lines
2.2 KiB
C++
//
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// 4.1.linear.container.cpp
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// modern c++ tutorial
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//
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// created by changkun at changkun.de
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// https://github.com/changkun/modern-cpp-tutorial
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//
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#include <iostream>
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#include <array>
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#include <vector>
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void foo(int *p, int len) {
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for (int i = 0; i != len; ++i) {
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std::cout << p[i] << std::endl;
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}
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}
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int main() {
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std::vector<int> v;
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std::cout << "size:" << v.size() << std::endl; // output 0
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std::cout << "capacity:" << v.capacity() << std::endl; // output 0
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// As you can see, the storage of std::vector is automatically managed and
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// automatically expanded as needed.
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// But if there is not enough space, you need to redistribute more memory,
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// and reallocating memory is usually a performance-intensive operation.
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v.push_back(1);
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v.push_back(2);
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v.push_back(3);
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std::cout << "size:" << v.size() << std::endl; // output 3
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std::cout << "capacity:" << v.capacity() << std::endl; // output 4
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// The auto-expansion logic here is very similar to Golang's slice.
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v.push_back(4);
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v.push_back(5);
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std::cout << "size:" << v.size() << std::endl; // output 5
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std::cout << "capacity:" << v.capacity() << std::endl; // output 8
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// As can be seen below, although the container empties the element,
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// the memory of the emptied element is not returned.
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v.clear();
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std::cout << "size:" << v.size() << std::endl; // output 0
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std::cout << "capacity:" << v.capacity() << std::endl; // output 8
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// Additional memory can be returned to the system via the shrink_to_fit() call
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v.shrink_to_fit();
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std::cout << "size:" << v.size() << std::endl; // output 0
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std::cout << "capacity:" << v.capacity() << std::endl; // output 0
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std::array<int, 4> arr= {1,4,3,2};
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//int len = 4;
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//std::array<int, len> arr = {1,2,3,4}; // illegal, size of array must be constexpr
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// C style parameter passing
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// foo(arr, arr.size()); // illegal, cannot convert implicitly
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foo(&arr[0], arr.size());
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foo(arr.data(), arr.size());
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// more usage
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std::sort(arr.begin(), arr.end());
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for(auto &i : arr)
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std::cout << i << std::endl;
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return 0;
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}
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