CODEWITHSUNDEEP
c++stringfilesstream
Henrik Hillestad Løvold
Henrik Hillestad Løvold

Reputation: 1281

Splitting a compact string into individual ints

I am attempting to write a program that reads a file line by line, and storing the contents of each line as individual integer values. A typical line might look like this:

7190007400050083

The following snippet from my code reads a single line from the file with numbers in it:

std::ifstream file;
file.open("my_file_with_numbers");
std::string line;
file >> line;

I want the string to be split up into separate values and store them as integers in a vector. I have looked across the internet, but found no solutions. Help is much appreciated.

Upvotes: -2

Views: 81

Answers (1)

Some programmer dude
Some programmer dude

Reputation: 409176

Assuming you want one value per digit, you can do e.g.

std::vector<int> vec(line.length());
std::transform(begin(line), end(line), begin(vec),
               [](char const& ch)
               {
                   return ch - '0';
               });

For the input string "7190007400050083" you will get the vector { 7, 1, 9, 0, 0, 0, 7, 4, 0, 0, 0, 5, 0, 0, 8, 3 }.

Otherwise, how large can the numbers be? Can they be negative? Why not read it directly into integers to begin with, why use a string?

For this, and again with an assumption that the values will all fit in a 64-bit unsigned integer type:

std::vector<unsigned long long> vec;
unsigned long long value;
while (file >> value)
{
    vec.push_back(value);
}

The above is the naive and beginner solution, but there are other ways:

std::vector<unsigned long long> vec(
        std::istream_iterator<unsigned long long>(file),
        std::istream_iterator<unsigned long long>());

For arbitrary length integer values, you need a "bignum" library like GMP.

Upvotes: 4

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