• deprecated ungetc at the beginning of a binary file

    From Vincent Lefevre@21:1/5 to All on Tue Sep 14 13:44:29 2021
    I can see since C99 (at least):

    deprecate ungetc at the beginning of a binary file

    [Future library directions]
    The use of ungetc on a binary stream where the file position
    indicator is zero prior to the call is an obsolescent feature.

    Dropping this feature is a bad idea and is likely to introduce
    subtle bugs (possibly security issues) in software, which includes
    GNU MPFR in mpfr_inp_str, for instance if some binary stream is
    redirected to /dev/null (most streams are probably text streams,
    but this is not controlled by libraries like MPFR).

    Indeed, in practice, one may wish to handle EOF and other error
    conditions after calling ungetc, which is currently safe, since
    the standard says for EOF:

    If the value of c equals that of the macro EOF, the operation fails
    and the input stream is unchanged.

    Code could easily be fixed by changing

    ungetc (c, stream);


    if (c != EOF)
    ungetc (c, stream);

    But why changing something that makes sense to undefined behavior,
    probably without any benefit (no performance issues...)?

    Shouldn't the C language tend to more safety?

    Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
    100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
    Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)