Jerry Jerry - 2 months ago 22
C++ Question

Best way to read binary file c++ though input redirection

I am trying to read a large binary file thought input redirection(Stdin) at runtime. Stdin is mandatory.

./a.out < input.bin

So far I have used fgets. But fgets skips blanks and newline. I want to include both.My currentBuffersize could dynamically vary.

FILE * inputFileStream = stdin;
int currentPos = INIT_BUFFER_SIZE;
int currentBufferSize = 24; // opt
unsigned short int count = 0; // As Max number of packets 30,000/65,536
while (!feof(inputFileStream)) {
char buf[INIT_BUFFER_SIZE]; // size of byte
fgets(buf, sizeof(buf), inputFileStream);
cout<<buf;
cout<<endl;
}


Thanks in Advance

Answer

If it were me I would probably do something similar to this:

const std::size_t INIT_BUFFER_SIZE = 1024;

int main()
{
    try
    {
        // on some systems you may need to reopen stdin in binary mode
        // this is supposed to be reasonably portable
        std::freopen(nullptr, "rb", stdin);

        if(std::ferror(stdin))
            throw std::runtime_error(std::strerror(errno));

        std::size_t len;
        std::array<char, INIT_BUFFER_SIZE> buf;

        // somewhere to store the data
        std::vector<char> input;

        // use std::fread and remember to only use as many bytes as are returned
        // according to len
        while((len = std::fread(buf.data(), sizeof(buf[0]), buf.size(), stdin)) > 0)
        {
            // whoopsie
            if(std::ferror(stdin) && !std::feof(stdin))
                throw std::runtime_error(std::strerror(errno));

            // use {buf.data(), buf.data() + len} here
            input.insert(input.end(), buf.data(), buf.data() + len); // append to vector
        }

        // use input vector here
    }
    catch(std::exception const& e)
    {
        std::cerr << e.what() << '\n';
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}

Note you may need to re-open stdin in binary mode not sure how portable that is but various documentation suggests is reasonably well supported across systems.

Comments