objected映射到unordered_map，是系统初始化的吗？

Question

使用unordered_map映射到结构时，想知道映射到的对象是否被系统初始化。我在 g++ 4.7.3 中使用 Ubuntu 12.04 64 位。谢谢。

#include <iostream>
#include <unordered_map>

struct strDum {
    uint a[3];
    int id;
};

int main (int argc, char *argv[])
{
    int i;
    char cmd[100];
    std::unordered_map<std::string,strDum> mymap;
    mymap["john"].a[0] = 10;
    mymap["john"].a[1] = 20;
    mymap["john"].a[2] = 30;
    printf("%d\n", mymap[argv[1]].a[1]);
    return 0;
}

Answer 1

您正在以下几行std::unordered_map mymap 中初始化

mymap["john"].a[0] = 10;
mymap["john"].a[1] = 20;
mymap["john"].a[2] = 30;

Answer 2

如果在使用std::unordered_map::operator[], the mapped value is value-initialized时执行插入。

Returns a reference to the value that is mapped to a key equivalent to key, performing an insertion if such key does not already exist.

If an insertion is performed, the mapped value is value-initialized (default-constructed for class types, zero-initialized otherwise) and a reference to it is returned.

objected映射到unordered_map，是系统初始化的吗？

objected mapped to in unordered_map, is it initialized by the system?

c++

unordered-map