fread_charT_fread_charFreadCharFreadChar (Operator)

Name

fread_charT_fread_charFreadCharFreadChar — Read one character from a text file.

Signature

fread_char( : : FileHandle : Char)

Description

The operator fread_charfread_charFreadCharFreadCharFreadChar reads a character from the input file defined by FileHandleFileHandleFileHandleFileHandlefileHandle. The input file must have been opened with open_fileopen_fileOpenFileOpenFileOpenFile in text format.

The read character or the control character sequence 'eof' is returned in parameter CharCharCharCharcharVal. The operator fread_charfread_charFreadCharFreadCharFreadChar respects the encoding of the characters, unless the file was opened with the option 'ignore_encoding'"ignore_encoding""ignore_encoding""ignore_encoding""ignore_encoding" (see open_fileopen_fileOpenFileOpenFileOpenFile). Thus, when opened with the correct encoding the operator fread_charfread_charFreadCharFreadCharFreadChar returns multi-byte characters at once. If necessary, the character is transcoded into the current encoding of the HALCON library (see set_system(::'filename_encoding',<encoding>:)set_system("filename_encoding",<encoding>)SetSystem("filename_encoding",<encoding>)SetSystem("filename_encoding",<encoding>)SetSystem("filename_encoding",<encoding>)).

When the file was opened with encoding mode 'ignore_encoding'"ignore_encoding""ignore_encoding""ignore_encoding""ignore_encoding", CharCharCharCharcharVal always returns one byte without any interpretation or transcoding. This is useful for reading a file with special control bytes in a kind of raw mode. If no character can be read because the end of the file is reached, fread_charfread_charFreadCharFreadCharFreadChar returns the control character sequence 'eof'"eof""eof""eof""eof" in CharCharCharCharcharVal.

The operator fread_charfread_charFreadCharFreadCharFreadChar emits a low-level error message, when the next byte or byte sequence does not represent a valid code point in the specified encoding. Despite of the low-level error message, the operator will not fail and CharCharCharCharcharVal will contain the next byte. Furthermore, the operator also emits a low-level error message, when the read character cannot be transcoded without loss of information into the current encoding of the HALCON library. This can only happen when the file is UTF-8 encoded and the current encoding of the HALCON library is 'locale'"locale""locale""locale""locale" (see set_system(::'filename_encoding','locale':)set_system("filename_encoding","locale")SetSystem("filename_encoding","locale")SetSystem("filename_encoding","locale")SetSystem("filename_encoding","locale")).

Execution Information

Multithreading type: reentrant (runs in parallel with non-exclusive operators).
Multithreading scope: global (may be called from any thread).
Processed without parallelization.

Parameters

FileHandleFileHandleFileHandleFileHandlefileHandle (input_control) file → (handle)

File handle.

CharCharCharCharcharVal (output_control) string → (string)

Read character, which can be multi-byte or the control string 'eof'"eof""eof""eof""eof".

Example (HDevelop)

* Read a text file character by character.
open_file (FileName, 'input', FileHandle)
repeat
    fread_char (FileHandle, Char)
until (Char == 'eof')
close_file (FileHandle)

Result

If an input file is open, the operator fread_char returns 2 (H_MSG_TRUE). Otherwise, an exception is raised. Encoding errors have no influence on the result state.