Re: Reading Large file

Hi!

I wonder, why there is no answer in the last weeks. I just stumbled over
this thread.

smilesonisamal@gmail.com schrieb:


Instead of reading one character at a time, you can use the "read"
procedure to read any number of characters at a time. Since you have a a
fixed record length, this length is a good candidate for the reading length.

Reading a file using the C++ standard iostreams:

#include <vector>
#include <istream> //for reading
#include <iostream> //console streams, cout
#include <fstream> //for files
#include <stdexcept> //some exceptions, runtime_error

static const size_t RECORD_SIZE = 100; //fixed size record length

typedef std::vector<char> RecordBuffer; //array of char

void handleRecord(RecordBuffer const& buffer)
{
    // .. whatever ..
    // access to chars via buffer.at(index)
    std::cout << "read one record\n";
}

void readRecord(std::istream& stream, RecordBuffer& buffer)
{
    buffer.resize(RECORD_SIZE);
    stream.read(&buffer.front(), RECORD_SIZE);
}

void readAndHandleFile(const char* const filename)
{
    std::ifstream file(filename);
    if( ! file)
        throw std::runtime_error("could not open file");

    while(true)
    {
        RecordBuffer buffer;
        readRecord(file, buffer);
        if( ! file)
            break;
        handleRecord(buffer);
    }
    file.close();
}

int main(int argc, char* argv[])
{
    try
    {
        if(argc>1)
            readAndHandleFile(argv[1]);

        return 0; //0 means successful execution
    }
    catch(std::exception const& e)
    {
        std::cout << "ERROR: " << e.what() << '\n';
    }
    catch(...)
    {
        std::cout << "UNKNOWN ERROR\n";
    }
    return -1; //signal error
}

HTH,
Frank

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