c++11 share_ptr as value a map key - pointers

Question

I just insert pValue to map next i get it from map ,and its value should be 20 ,but not, why?
typedef shared_ptr<BaseObject> PtrValue;
class CodeExecuteContext{
public:
map<string,PtrValue> varIdentPool;
};
class BaseInteger :public BaseObject{
public:
int value;
BaseInteger(int val):value(val){
enumObjType = INT;
};
};
...
PtrValue pValue = rightNode->executeCode(context);
context.varIdentPool.insert(make_pair(leftNode.idName,pValue));
BaseInteger * baseInteger = (BaseInteger *) pValue.get();
cout << "==AssignmentASTFork== insert [ " << leftNode.idName << " , " << baseInteger->value << " ]" <<endl;
map<string,PtrValue>::iterator it;
for (it = context.varIdentPool.begin() ; it!=context.varIdentPool.end();it++) {
BaseInteger * baseInteger = (BaseInteger *) it->second.get();
cout << "[key : " << it->first << ", value : " << baseInteger->value << endl;
}
result:
==AssignmentASTFork== insert [ arg , 20 ]
[key : arg, value : 32742]

Answer 1

The map::insert function returns "pair", where the boolean from the pair indicates whether the element has been inserted or not. If the boolean is true, it has been inserted. If the key already existed, the boolean will be false and the key-value pair has not been inserted.
Try "auto insertResult = context.varIdentPool.insert(make_pair(leftNode.idName,pValue));"
If insertResult.second == false, the key already existed.
The iterator (insertResult.first) will always point to the item from the map.
With that iterator you can alter the value from the map by "insertResult.first->second = newValue"