CODEWITHSUNDEEP
c++unordered-map
packetie
packetie

Reputation: 5069

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

When using unordered_map to map to a structure, wonder if the object mapped to is initialized by the system. I am using Ubuntu 12.04 64bit with g++ 4.7.3. Thanks. 

#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;
}

Upvotes: 1

Views: 95

Answers (2)

songyuanyao
songyuanyao

Reputation: 172894

If an insertion is performed when using std::unordered_map::operator[], the mapped value is value-initialized.

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.

Upvotes: 1

Steephen
Steephen

Reputation: 15824

You are initializing your std::unordered_map mymap in following lines

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

Upvotes: 0

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