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manual: Document dprintf and vdprintf

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Reviewed-by: Carlos O'Donell <carlos@redhat.com>
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Florian Weimer 2024-08-13 15:52:34 +02:00
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manual/stdio.texi
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@ -2525,6 +2525,26 @@ store the result in which case @code{-1} is returned. This was
changed in order to comply with the @w{ISO C99} standard. changed in order to comply with the @w{ISO C99} standard.
@end deftypefun @end deftypefun
@deftypefun dprintf (int @var{fd}, @var{template}, ...)
@standards{POSIX, stdio.h}
@safety{@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This function formats its arguments according to @var{template} and
writes the result to the file descriptor @var{fd}, using the
@code{write} function. It returns the number of bytes written, or a
negative value if there was an error. In the error case, @code{errno}
is set appropriately. The possible @code{errno} values depend on the
type of the file descriptor @var{fd}, in addition to the general
@code{printf} error codes.
The number of calls to @code{write} is unspecified, and some @code{write}
calls may have happened even if @code{dprintf} returns with an error.
@strong{Portability Note:} POSIX does not require that this function is
async-signal-safe, and @theglibc{} implementation is not. However, some
other systems offer this function as an async-signal-safe alternative to
@code{fprintf}. @xref{POSIX Safety Concepts}.
@end deftypefun
@node Dynamic Output @node Dynamic Output
@subsection Dynamically Allocating Formatted Output @subsection Dynamically Allocating Formatted Output
@ -2738,6 +2758,13 @@ The @code{obstack_vprintf} function is the equivalent of
as for @code{vprintf}. as for @code{vprintf}.
@end deftypefun @end deftypefun
@deftypefun int vdprintf (int @var{fd}, const char *@var{template}, va_list @var{ap})
@standards{POSIX, stdio.h}
@safety{@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The @code{vdprintf} is the equivalent of @code{dprintf}, but processes
an argument list.
@end deftypefun
Here's an example showing how you might use @code{vfprintf}. This is a Here's an example showing how you might use @code{vfprintf}. This is a
function that prints error messages to the stream @code{stderr}, along function that prints error messages to the stream @code{stderr}, along
with a prefix indicating the name of the program with a prefix indicating the name of the program