Re: Documenting sscanf()'s and fscanf's underflow

On Sunday 24 May 2026 22:38:16 (+02:00), mickmackusa wrote:

Hi all, may I request that the documentation pages for sscanf() and fscanf() be reviewed?

Thank you for the detailed documentation on SO and invoking some initiative here on the list.

I have been doing a fair amount of Google searching, but either my keywords

are not ideal or there really is no mention of this floating around (even

the C++ pages that I read don't mention it).

C++ might be a red herring, sscanf is more ANSI C and for PHP the original code from TCL8.3.0: <https://www.tcl-lang.org/software/tcltk/relnotes/tcl8.3.0.txt> "The main site for Tcl/Tk source distributions is SourceForge" [1], that version's sources and manual: * tcl8.3.0.tar.gz -- 2001-07-30 2.5 MB * tcl8.3.0.html.tar.gz -- 2001-07-30 582.1 kB <https://sourceforge.net/projects/tcl/files/Tcl/8.3.0/*> For sscanf ANSI C I have found

    The Unix Heritage Society <https://www.tuhs.org>

an invaluable resource to learn about ANSI draft interpretations as they have archives of Usenet comp.std.c in indexable hypertext documents as well as gzipped tarballs: <https://www.tuhs.org/Usenet/comp.std.c/> I found it helpful in context of PHP to understand the communication in the user's network (Usenet/USENIX network) with the Unix-to-Unix Copy Protocol (UUCP) and also the nomenclature of C and other computer lanugages standardization processes. To give an example for questions like why the PHP implementation of fscanf() might be reading one line at a time as you briefly mentioned off-list IIRC, I found a message 'Hints for using "scanf"' [2] that helped me to reflect such kind of thoughts. Let me illustrate with an excerpt of the exemplary message written by Martin Weitzel in January 1990:

If you want to analyze interactive (or unpredictable) input, my advice is to read a complete line with "fgets" (avoid "gets"!!) or read up to some other significant token with "gets/fgets". After that, use "sscanf" on the buffer you just read.

In our sources we can find the following lines:

    	buf = php_stream_get_line((php_stream *) what, NULL, 0, &len);
    	if (buf == NULL) {
    		RETURN_FALSE;
    	}
        	result = php_sscanf_internal(buf, format, argc, args, 0, return_value);

This is PHP's way of fgets() followed by sscanf() on the buffer, as illustrated by M. Weitzel back in 1990. As you requested, I illustrative now "reviewed" the manual page for the fscanf() function [3] in this regard:

Each call to fscanf() reads one line from the file.

Find out more about networked computing not only in comp.infosystems.www.authoring.cgi (check June 8 '95) but also in the comp.* hierarchy when you want to research in the archives. best -- hakre p.s. I took some time yesterday to document an example listing of how to make use of the "underflow behavior", e.g. for testing in GH-19088 [4] in case of interest. [1]: https://www.tcl-lang.org/software/tcltk/download.html [2]: https://www.tuhs.org/Usenet/comp.std.c/1990-January/000290.html [3]: https://web.archive.org/web/20170812235246/http://php.net/fscanf [4]: https://github.com/php/php-src/issues/19088#issuecomment-4534153067