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c++streamoperator-overloadingifstreamsyntactic-sugar

Extract from an ifstream without a temporary variable?

ifstream offers an overload of operator>> to extract values from the next line of the stream. However, I tend to find myself doing this often:

int index;
input >> index;
arr[index] = <something>;

Is there any way to get this data into the [index] without having to create this temporary variable?

Solution

  • You can write a function to extract the next value from an istream:

    template <typename T> // T must be DefaultConstructible
T read(std::istream& input) {
    T result;
    input >> result;
    return result;
}

    Then, you could just write:

    arr[read<int>(input)] = <something>;

    Although you should probably write

    arr.at(read<int>(input)) = <something>;

    Because otherwise you open yourself up to a buffer-overflow vulnerability. If the input file had an integer out of range, you'd be writing out of bounds.