Text_IO files consist of a stream of characters containing the following special control characters:
LF (line feed, 16#0A#) Line Mark FF (form feed, 16#0C#) Page Mark
A canonical Text_IO file is defined as one in which the following conditions are met:
LFis used only as a line mark, i.e. to mark the end of the line.
FFis used only as a page mark, i.e. to mark the end of a page and consequently can appear only immediately following a
LF(line mark) character.
LF(line mark) or
FF(line mark, page mark). In the former case, the page mark is implicitly assumed to be present.
A file written using Text_IO will be in canonical form provided that no
FF characters are written using
Put_Line. There will be no
FF character at the end of
the file unless an explicit
New_Page operation was performed
before closing the file.
A canonical Text_IO file that is a regular file (i.e., not a device or a pipe) can be read using any of the routines in Text_IO. The semantics in this case will be exactly as defined in the Ada Reference Manual, and all the routines in Text_IO are fully implemented.
A text file that does not meet the requirements for a canonical Text_IO file has one of the following:
FFcharacters not immediately following a
FFcharacters written by
Put_Line, which are not logically considered to be line marks or page marks.
FF, i.e. there is no explicit line mark or page mark at the end of the file.
Text_IO can be used to read such non-standard text files but subprograms
to do with line or page numbers do not have defined meanings. In
FF character that does not follow a
character may or may not be treated as a page mark from the point of
view of page and line numbering. Every
LF character is considered
to end a line, and there is an implied
LF character at the end of