Re: [Boost-users] Boost Format: format strings and character types

From: chun ping wang (cablepuff_at_[hidden])
Date: 2008-01-30 12:34:14

I think the first one won't work because %d is for decimal printing , and
char is a character. Format is a typesafe library so the document should say
any type safe format will work in here as in printf. But interesting find.

Instead this would.
 printf( "Using printf: ii=%d, cc=%d\n", ii, cc );
 cout << boost::format( "Using boost::format: ii=%1d%, cc=%2d%" ) %
     ii % cc << endl;

On Jan 30, 2008 4:29 AM, Daniel James <gmane.junk001_at_[hidden]> wrote:

> The documentation states that the same format string used with printf
> and boost::format should result in the same output in "almost all
> cases".
>
> My colleagues and I have found, though, that when a %d descriptor is
> used to print a char variable the result is as though a %c descriptor
> had been used -- printf and boost::format don't produce the same
> result.
>
> That is:
>
>  int ii(42);
>  char cc(42);
>
>  printf( "Using printf: ii=%d, cc=%d\n", ii, cc );
>  cout << boost::format( "Using boost::format: ii=%d, cc=%d" ) %
>      ii % cc << endl;
>
> Produces:
>
> Using printf: ii=42, cc=42
> Using boost::format: ii=42, cc=*
>
> So, it seems that boost::format deduces the format to be used for
> outputting cc from its type and ignores the format explicitly requested
> in the format.
>
> Is this working as intended? If so the documentation seems to me to be
> misleading.
>
> I also note that:
>
>  cout << boost::format( "As chars: ii=%c, cc=%c" ) % ii % cc << endl;
>
> Produces:
>
> As chars: ii=4, cc=*
>
> That is: the %c descriptor causes the value of ii (42) to be truncated
> to a single char. Also something of a surprise.
>
> My tests were carried out using boost 1.34.1 and Visual Studio 2005 on
> Windows.
>
> Cheers,
>  Daniel.
>
>
>
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