CODEWITHSUNDEEP
c++dictionary
Ryeanney
Ryeanney

Reputation: 1

map find() function if the wanted key is in the last position

I am a C++ beginner. I know that find() is used to search for a certain key. This function returns an iterator to the element if the element is found, else it returns an iterator pointing to the last position of the. map i.e map.end(). I read from websites that

if(it == mp.end())
    cout << "Key-value pair not present in map" ;
else
    cout << "Key-value pair present : "

What if the found key is in the end postition? How can it still work? Key is sorted in a certain order and I think the iterator traverses the sorted key to find the one we want. (is it correct?)

Upvotes: 0

Views: 76

Answers (2)

Kerch
Kerch

Reputation: 25

According to cplusplus.com , .end() Returns an iterator pointing to the past-the-end element in the sequence:

It does not point to an element in the container ( the map in your case ), rather points outside of it.

Upvotes: 1

mksteve
mksteve

Reputation: 13073

The result of all .end() in the stl is beyond the valid values. So end() will never be valid.

int arr[10];
// arr has valid indices 0,1,2,3,...,7,8,9
// arr[10] is not valid.
for( auto i = 0; i < 10; i++ ){
}

std::vector vec;
vec.resize( 10 );
// vec.end() is equivalent to arr[10] - not part of the vector
for( auto it = vec.begin(); vec != vec.end(); vec++ ) {
}

So lets re-write the array in the vector idiom

for( auto i = 0; &arr[i] != &arr[10]; i++ ){
}

Maps are more complicated, they have a different guard mechanism, but an iterator == end() never is valid.

Upvotes: 1

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