Reading a file in chunks

Question

char x[5];

ifstream i("test.txt", std::ifstream::binary);

while (i.read(x, sizeof(x))) { 
    ...
    bzero(x, sizeof(x));
}

If the file byte size is not a multiple of 5, the program fails to read the last chunk. How do I make sure to read that as well?

If end of file condition occurs on the input sequence (in which case, setstate(failbit|eofbit) is called). The number of successfully extracted characters can be queried using gcount(). http://en.cppreference.com/w/cpp/io/basic_istream/read — Richard Critten, Mar 10 '16 at 00:23
How do I incorporate that in here? Do I call i.gcount() inside the while block? — ExtremistEnigma, Mar 10 '16 at 00:34

score 0 · Answer 1 · answered Mar 10 '16 at 00:42

0

what about this:

std::ifstream fin("test.txt", std::ifstream::binary);
std::vector<char> x(5, 0);

while (fin.read(x.data(), x.size())) 
{
    std::streamsize s = fin.gcount();

    // do something with x's data
}

answered Mar 10 '16 at 00:42

Zoltán

678
4
15

Does not seem to work for some reason. Am I using a regular char array, would that make a difference? – ExtremistEnigma Mar 10 '16 at 02:58
this one won't work with regular char array, since `data()` is a built in function of a c++ container. – Zoltán Mar 10 '16 at 09:27
`fin.read(...)` evaluates to false on the last partial block (or eof). You need to process partial reads outside of the while loop `gcount()!=0` . – Richard Critten Mar 10 '16 at 11:06

Reading a file in chunks

1 Answers1