Cpp

vector memory layout

Source

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// vector.cpp
#include <vector>
#include <iostream>

void func(std::vector<unsigned long> &datas) {
    for (auto &data : datas) {
        data++;
    }
}

int main() {
    std::vector<unsigned long> v{01,02, 2, 3, 4,5,6};
    func(v);
    v.push_back(16);
    v.push_back(32);
    v.push_back(256);
    func(v);
    size_t size = v.size();
    std::cout << size << std::endl;
    size = v.capacity();
    std::cout << size << std::endl;
    return 0;
}

Debug

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> g++ -O1 vector.cpp -o vector

> gdb vector


(gdb) br func
(gdb) run

(gdb) x /4gx $rdi
0x7fffffffda50: 0x000055555556aeb0      0x000055555556aee8
0x7fffffffda60: 0x000055555556aee8      0x0000555555555499

(gdb) x /8gx 0x000055555556aeb0
0x55555556aeb0: 0x0000000000000001      0x0000000000000002
0x55555556aec0: 0x0000000000000002      0x0000000000000003
0x55555556aed0: 0x0000000000000004      0x0000000000000005
0x55555556aee0: 0x0000000000000006      0x000000000000f121

(gdb) c
(gdb) x /4gx $rdi
0x7fffffffda50: 0x000055555556aef0      0x000055555556af40
0x7fffffffda60: 0x000055555556af60      0x0000555555555499
(gdb) x /12gx 0x000055555556aef0
0x55555556aef0: 0x0000000000000002      0x0000000000000003
0x55555556af00: 0x0000000000000003      0x0000000000000004
0x55555556af10: 0x0000000000000005      0x0000000000000006
0x55555556af20: 0x0000000000000007      0x0000000000000010
0x55555556af30: 0x0000000000000020      0x0000000000000100

Layout

从调试的结果来看, vector 对象中包含三个指针: begin, end, capacity.

begin: 分配内存空间的首地址

end: 有效数据的截止地址

capacity: 分配内存空间的结束地址

  • 当内存空间不足, 会自动分配新的内存空间.
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