Re: [TUHS] pic anomalies

Re: [TUHS] pic anomalies

[Doug McIlroy]

According to K&R the behavior of % followed by something
unexpected is undefined. So the behavior of Ralph's example
is officially an accident. (It's uncharacteristic of Dennis
to have defined printf so that there was no guaranteed way
to get a literal % into a format.)

Doug

------------------------------------------------

Ralph Corderoy wrote:

    $ printf '%s\n' \
        .PS 'print sprintf("%.17g %.0f% % %%", 3.14, 42, 99)' .PE |
    > pic >/dev/null
    3.1400000000000001 42% % %%

Though that may seem odd to our modern C-standardised eyes, it's
understandable in that if it isn't a valid %f, etc., format specifier
then it's a literal percent sign.

Re: [TUHS] pic anomalies

[Doug McIlroy]

The use of %% to designate a literal % in printf is not
a recent convention. It was defined in K&R, first edition.

Doug

Ralph Cordery wrote:

Though that may seem odd to our modern C-standardised eyes, it's
understandable in that if it isn't a valid %f, etc., format specifier
then it's a literal percent sign.

Re: [TUHS] pic anomalies

[Clem Cole]

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On Mon, Dec 30, 2019 at 11:24 PM Doug McIlroy <doug@cs.dartmouth.edu> wrote:

> The use of %% to designate a literal % in printf is not
> a recent convention. It was defined in K&R, first edition.
>
FWIW, I still have an old (fading) copy of the galley proofs for the first
edition.  Page 147 (*Chapter 7 - Input and Output, Section 7.3 Formatted
Output - Printf*) first full paragraph on the page:

If the character after the % is not a conversion character, that character
is printed: thus % may be printed by %%.



>
> Doug
>
> Ralph Cordery wrote:
>
> Though that may seem odd to our modern C-standardised eyes, it's
> understandable in that if it isn't a valid %f, etc., format specifier
> then it's a literal percent sign.
>
>

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