CODEWITHSUNDEEP
c++unicodeasciiiostreamifstream
Malkavian
Malkavian

Reputation: 372

Reading From A File Which Contains Unicode Characters

I have this huge file which contains unicode strings at the beginning (first ~10,000 character or so) I don't care about the unicode part, parts I'm interested aren't unicode but whenever I try to read those parts I get '=', and if I were to load the entire file to char array and write to to some temporary file (without altering the data) with ofstream I get incorrect data actually all I get is a text file filled with Í If I were to remove the unicode part manually everything works fine, So it seems ifstream cannot deal with streams which contains unicode data, but if this assumption is true, is there any way to work on this file introducing a new library to my project?

Thanks,

EDIT: Here's a sample code, program reads from this file which contains characters (some, not all) that can't be represented in ASCII.

ifstream inFile("somefile");
inFile.seekg(0,ios_base::end);
size_t size = inFile.tellg();
inFile.seekg(0,ios_base::beg);
char *book = new  char[size];
inFile.read(book,size);
for (int i = 0; i < size; i++) {
  cout << book[i] << " " << i << endl; //book[i] will always be '='
}
ofstream outFile("TEST.txt");
outFile.write(book,size);
outFile.close();

Upvotes: 2

Views: 1195

Answers (2)

nanda
nanda

Reputation: 804

A text file is generally in just one encoding utf-8, utf-16 (big or little endian) or utf-32 (big or little) or ASCII or other ANSI code pages. Mixing of encoding is only possible in some custom ways.

That said, you will have to read both the data that you need and that you don't in the same encoding. If you know the format is utf-8 you could, depending on what you are going to do with the data, read the file as a binary file into char buffer piece by piece. Then you could API(s) like strnextc (on windows. equivalent API must be available on other platforms) to move character by character on the buffer. Once you reach the end - you could move the balance to the front of the buffer and load the rest of the buffer from the file.

In fact you could use the above approach in general for any encoding. But for utf-16, you could try using wifstream - provided the endianess of the file and the platform you would be running on is the same. And you need to check if the implementation of wifstream is good at handling change in endiness and is able to take care of BOM (byte order mark) - 2 byte sequence ("FE FF" or "FF FE") that is generally present at the beginning of a file - leave alone surrogate pairs.

Upvotes: 0

dda
dda

Reputation: 6203

Keith Thompson's question is very important. Depending on which Unicode encoding, writing a small C routine that reads (and discards) the Unicode characters can be trivial, or slightly more complex.

Supposing the encoding is UTF-8, you will have a problem determining when to stop discarding because ASCII is a subset of UTF-8, so any time you encounter an ASCII char, you might be tempted to say "this is it, we're back in ASCII land" and the next char still might be still outside the ASCII range.

So you need to read the file and determine where the last character>127 is. Anything after that is plain ASCII -- hopefully.

Upvotes: 4

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