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Document interaction with GCC built-ins in the Customizing Printf

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section of the manual.
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Martin Sebor 2018-06-29 10:45:19 -06:00
parent bac15a72fc
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@ -1,3 +1,8 @@
2018-06-29 Martin Sebor <msebor@redhat.com>
* manual/stdio.texi (Customizing Printf): Mention interaction
with GCC built-ins.
2018-06-29 Maciej W. Rozycki <macro@mips.com>
[BZ #23307]

16
manual/stdio.texi
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@ -2962,7 +2962,11 @@ The facilities of this section are declared in the header file
@strong{Portability Note:} The ability to extend the syntax of
@code{printf} template strings is a GNU extension. ISO standard C has
nothing similar.
nothing similar. When using the GNU C compiler or any other compiler
that interprets calls to standard I/O functions according to the rules
of the language standard it is necessary to disable such handling by
the appropriate compiler option. Otherwise the behavior of a program
that relies on the extension is undefined.
@node Registering New Conversions
@subsection Registering New Conversions
@ -3016,9 +3020,13 @@ function when this format specifier appears in the format string.
The return value is @code{0} on success, and @code{-1} on failure
(which occurs if @var{spec} is out of range).
You can redefine the standard output conversions, but this is probably
not a good idea because of the potential for confusion. Library routines
written by other people could break if you do this.
@strong{Portability Note:} It is possible to redefine the standard output
conversions but doing so is strongly discouraged because it may interfere
with the behavior of programs and compiler implementations that assume
the effects of the conversions conform to the relevant language standards.
In addition, conforming compilers need not guarantee that the function
registered for a standard conversion will be called for each such
conversion in every format string in a program.
@end deftypefun
@node Conversion Specifier Options