vector capacity变化规律

是以2的n次方来变化的

#include <vector>
#include <iostream>

int main() {
    std::vector<int> vec;
    std::cout << "Initial capacity: " << vec.capacity() << std::endl;


    for (int i = 0; i < 100; ++i) {
        vec.push_back(i);
        std::cout << vec.size() << " " << vec.capacity() << std::endl;
    }

    return 0;
}

Initial capacity: 0
1 1
2 2
3 4
4 4
5 8
6 8
7 8
8 8
9 16
10 16
11 16
12 16
13 16
14 16
15 16
16 16
17 32
18 32
19 32
20 32
21 32
22 32
23 32
24 32
25 32
26 32
27 32
28 32
29 32
30 32
31 32
32 32
33 64
34 64
35 64
36 64
37 64
38 64
39 64
40 64
41 64
42 64
43 64
44 64
45 64
46 64
47 64
48 64
49 64
50 64
51 64
52 64
53 64
54 64
55 64
56 64
57 64
58 64
59 64
60 64
61 64
62 64
63 64
64 64
65 128
66 128
67 128
68 128
69 128
70 128
71 128
72 128
73 128
74 128
75 128
76 128
77 128
78 128
79 128
80 128
81 128
82 128
83 128
84 128
85 128
86 128
87 128
88 128
89 128
90 128
91 128
92 128
93 128
94 128
95 128
96 128
97 128
98 128
99 128
100 128