char array in C++

Question

In C++ can I read from file which contains integers and store it in a char array[] ?

Answer 1

Yes, it is possible to store numbers from a file in a char array:

#include <fstream>
#include <iterator>
#include <algorithm>

int main(int argc, char* argv[])
{
    std::ifstream in("input.txt");
    char arr[100];
    char* end = std::copy(std::istream_iterator<int>(in),
                          std::istream_iterator<int>(),
                          arr);
    return 0;
}

There are two issues here. One, you must know at compile time the size of your array. Two, each of the input numbers must fit into a char. Note that this is formatted input, so the valid range is not 0-255 or even 0-127. It's a valid character, so '0', '2', 'a', 'C' and so on are valid inputs for each character.

Maybe what you want is to read your file into a std::vector<std::string>?

#include <fstream>
#include <iterator>
#include <algorithm>
#include <vector>
#include <string>

int main(int argc, char* argv[])
{
    std::ifstream in("input.txt");
    std::vector<std::string> vec;
    std::copy(std::istream_iterator<int>(in),
              std::istream_iterator<int>(),
              std::back_inserter(vec));
    std::transfrom(vec.begin(), vec.end(),
                   vec.begin(),
                   my_transform());
    return 0;
}

Here we read the numbers into std::vector<std::string>. Then, we manipulate each string representation of a number through the my_transform functor. You define the functor as a simple struct that defines std::string operator()(const std::string&). The function-call operator takes a number and is expected to return the manipulation of the number, however you wish to change the number.

Answer 2

Yes. As long as your integers are small enough to be represented as a byte. If not, they higher order bytes will likely be lost.