I have a hash map defined as
class KeyType {
int key;
mutable bool flag;
KeyType(int key) : key(key), flag(false) {}
void setFlag() const { flag = true; }
};
struct KeyType_hasher {
size_t operator()(const KeyType& s) const {
return static_cast<size_t> key;
}
};
struct KeyType_equal {
size_t operator()(const KeyType& s1, const KeyType& s2) const {
return s1.key == s2.key;
}
};
typedef hash_map<KeyType , ValueType, KeyType_hasher, KeyType_equal > KeyValueMap;
Later on in the code I have a place where I have to loop though the map and apply a function to each value I find. Based on the function's outcome, I have to modify the key at the iterator as well.
KeyValueMap theMap;
// theMap[key1] = value1;
// theMap[key2] = value2;
// theMap[key3] = value3;
for(KeyValueMap::iterator i = theMap.begin(); i != theMap.end(); ++i) {
if(true == ValueFunction(i->second))
i->first.setFlag();
}
My question is, would that be the right way of modifying the key, if I have to? Does it have any bad side effects?
You'd have to remove the element from the container and re-add it with the new key.
None of the C++ associative containers support changing the key in a significant way (where significant means the change alters the results of the hash in a hashed container or the comparrsion in an ordered container).
If you did modify the key (by circumventing the const correctness system in some way) you'd get unpredictable results from lookups.