Operator Reference
fread_char (Operator)
fread_char — Read one character from a text file.
Signature
fread_char( : : FileHandle : Char)
Description
The operator fread_char reads a character from the input
file defined by FileHandle.
The input file must have been opened with open_file in text format.
The read character or the control character sequence 'eof' is returned in
parameter Char.
The operator fread_char respects the encoding of the characters,
unless the file was opened with the option 'ignore_encoding'
(see open_file).
Thus, when opened with the correct encoding the operator fread_char
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>:)).
When the file was opened with encoding mode 'ignore_encoding',
Char 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_char returns the control character sequence 'eof' in
Char.
The operator fread_char 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 Char 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'
(see set_system(::'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
FileHandle (input_control) file → (handle)
File handle.
Char (output_control) string → (string)
Read character, which can be multi-byte or the control string '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.
Possible Predecessors
Possible Successors
Alternatives
fread_string,
read_string,
fread_line
See also
open_file,
close_file,
fread_string,
fread_line
Module
Foundation