CPP File Handling & Standard Template Library (STL) 2

Question 1

Which STL container provides O(1) average-case insertion, deletion, and lookup?

Accepted Answer

std::unordered_map

Answer

std::unordered_map uses a hash table internally, giving O(1) average-case for these operations.

Question 2

What does std::ifstream::seekg() do?

Accepted Answer

Sets the get pointer position

Answer

seekg() repositions the get (read) pointer within an input stream.

Question 3

Which STL algorithm removes duplicate consecutive elements from a range?

Accepted Answer

std::unique

Answer

std::unique collapses consecutive duplicates to single elements and returns an iterator to the new end.

Question 4

What is the return type of std::vector::emplace_back() in C++17?

Accepted Answer

reference

Answer

In C++17, emplace_back() was changed to return a reference to the inserted element.

Question 5

Which file open mode flag creates a new file and truncates it if it already exists?

Accepted Answer

std::ios::trunc

Answer

std::ios::trunc discards any existing content when the file is opened.

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