ifstream and oftream issue - c++

Question

Just this:
int size = getFileSize(path); //Listed below
ifstream fs(path, ios::in);
ofstream os(path2, ios::out);
//Check - both streams are valid
char buff[CHUNK_SIZE]; //512
while (size > CHUNK_SIZE)
{
fs >> buff;
os << buff;
size -= CHUNK_SIZE;
}
char* dataLast = new char[size];
fs>>dataLast;
os<<dataLast;
fs.close();
os.close();
//Found on SO, works fine
int getFileSize(string path)
{
FILE *pFile = NULL;
if (fopen_s( &pFile, path.c_str(), "rb" ))
{
return 0;
}
fseek( pFile, 0, SEEK_END );
int Size = ftell( pFile );
fclose( pFile );
return Size;
}
File at path2 is corrupted and less then 1 Kb. (initial file is 30Kb);
I don't need advices how to copy file, I am curios what is wrong about this example.

Answer 1

First an important warning: Never (as in really never) use the formatted input operator for char* without setting the width()! You open yourself up to a buffer overrun. This is basically the C++ version of writing gets() which was bad enough to be removed (not just deprecated) from the C standard! If you insist in using formatted input with char* (normally you are much better off using std::string), set the width, e.g.:
char buffer[512];
in >> std::setw(sizeof(buffer) >> buffer;
OK, with this out of the way: it seems you actually want to change two important things:
You probably don't want to use formatted input, i.e., operator>>(): the formatted input operators start off with skipping whitespace. When reading into char* it also stops when reaching a whitespace (or when the width() is non-zero when having read a much characters and still space to store a terminating zero; note that the set width() will be reset to 0 after each of these reads). That is you probably want to use unformatted input, e.g., in.read(buffer, sizeof(buffer)) which sets in.gcount() to the number of characters actually read which may be less then size parameter, e.g., at the end of the stream.
You probably should open the file in std::ios_base::binary mode. Although it doesn't matter on some systems (e.g., POSIX systems) on some systems reading in text mode merges a line end sequence, e.g. \r\n on Windows, into the line end character \n. Likewise, when writing a \n in text mode, it will be replaced by a line end sequence on some system, i.e., you probably also want to open the output stream in text mode.

Answer 2

Th input and output operators, when used with strings (like buff is from the libraries point of view), reads space-delimited words, only.
If you want to read chunks, then use std::istream::read, and use std::istream::gcount to get the number of bytes actually read. Then write with std::ostream::write.
And if the data in the file is binary, you should use the binary open mode.