How do you identify the file content as being in ASCII or binary using C++?
If a file contains only the decimal bytes 9–13, 32–126, it's probably a pure ASCII text file. Otherwise, it's not. However, it may still be text in another encoding.
If, in addition to the above bytes, the file contains only the decimal bytes 128–255, it's probably a text file in an 8-bit or variable-length ASCII-based encoding such as ISO-8859-1, UTF-8 or ASCII+Big5. If not, for some purposes you may be able to stop here and consider the file to be binary. However, it may still be text in a 16- or 32-bit encoding.
If a file doesn't meet the above constraints, examine the first 2–4 bytes of the file for a byte-order mark:
FE FF
, the file is tentatively UTF-16 BE.FF FE
, and the following two bytes are not hex 00 00
, the file is tentatively UTF-16 LE.00 00 FE FF
, the file is tentatively UTF-32 BE.FF FE 00 00
, the file is tentatively UTF-32 LE.If, through the above checks, you have determined a tentative encoding, then check only for the corresponding encoding below, to ensure that the file is not a binary file which happens to match a byte-order mark.
If you have not determined a tentative encoding, the file might still be a text file in one of these encodings, since the byte-order mark is not mandatory, so check for all encodings in the following list:
If, after all these checks, you still haven't determined an encoding, the file isn't a text file in any ASCII-based encoding I know about, so for most purposes you can probably consider it to be binary (it might still be a text file in a non-ASCII encoding such as EBCDIC, but I suspect that's well outside the scope of your concern).