How to read a file in multiple chunks until EOF (C++)

Question

So, here\'s my problem: I want to make a program that reads chunks of data from a file. Let\'s say, 1024 bytes per chunk. So I read the first 1024 bytes, perform various operati

Answer 1

Accepted answer doesn't work for me - it doesn't read last partial chunk. This does:

void readFile(std::istream &input, UncompressedHandler &handler) {
    std::vector<char> buffer (1024,0); //reads only 1024 bytes at a time
    while (!input.eof()) {
        input.read(buffer.data(), buffer.size());
        std::streamsize dataSize = input.gcount();
        handler({buffer.begin(), buffer.begin() + dataSize});
    }
}

Here UncompressedHandler accepts std::string, so I use constructor from two iterators.

Answer 2

I think you missed up that there is a pointer points to the last place you've visit in the file , so that when you read for the second time you will not start from the first , but from the last point you've visit . Have a look to this code

std::ifstream fin("C:\\file.txt");
char buffer[1024]; //I prefer array more than vector for such implementation

fin.read(buffer,sizeof(buffer));//first read get the first 1024 byte

fin.read(buffer,sizeof(buffer));//second read get the second 1024 byte

so that how you may think about this concept .

Answer 3

You can do this with a loop:

std::ifstream fin("C:\\file.txt", std::ifstream::binary);
std::vector<char> buffer (1024,0); //reads only the first 1024 bytes

while(!fin.eof()) {
    fin.read(buffer.data(), buffer.size())
    std::streamsize s=fin.gcount();
    ///do with buffer
}

##EDITED

http://en.cppreference.com/w/cpp/io/basic_istream/read