QHash<key, value> hash;
if (hash.insert(Key, Value) == hash.end())
{
  // failed
}
else
{
  // succeeded
}

Well, thanks for the workaround.

@jsulm
Hello,
I've looked source code.

1. QHash::insert() just return result of called QHash::insertMulti() (line 1011).
2. QHash::insertMulti(), in turn, returns an iterator, in the constructor of which the result of calling function createNode() is passed (line 781).
3. createNode() returns a pointer to the Node created by the new operator (lines 548, 551).

As you can see there is no check for successful memory allocation. Maybe throws an exception?

Based on QHash size you can know value is inserted or not.
if inserted size becomes +1 to previous size if not size remains same as previous size.

int mapSize;
QHash<key,value> hash;
mapSize = hash.size();

hash.insert(key,Value);
if(hash.size()==mapSize+1)
{
//inserted succeeded
mapSize = hash.size();

}else{
//insertFailed
}