[patch] printf.3: correctly describe the meaning of a negative precision

[patch] printf.3: correctly describe the meaning of a negative precision

[Christopher Hall]

The printf(3) manpage says that a negative precision is taken to be
zero, whereas printf(3p) says that a negative precision is taken as if
the precision were omitted.  glibc agrees with the latter (posix)
specification.

Test code:

    printf("%f\n",42.0);      // "42.000000"
    printf("%.*f\n",0,42.0);  // "42"
    printf("%.*f\n",-1,42.0); // "42.000000"

This patch corrects the explanation to match what actually happens.

diff --git i/man3/printf.3 w/man3/printf.3
index f5e96d3..2c86bf1 100644
--- i/man3/printf.3
+++ w/man3/printf.3
@@ -409,8 +409,9 @@ Instead of a decimal digit string one may write
"*" or "*mquot;
 is given in the next argument, or in the m-th argument, respectively,
 which must be of type
 .IR int .
-If the precision is given as just \(aq.\(aq, or the precision is negative,
-the precision is taken to be zero.
+If the precision is given as just \(aq.\(aq, the precision is taken to
+be zero.  A negative precision is taken as if the precision were
+omitted.
 This gives the minimum number of digits to appear for
 .BR d ,
 .BR i ,


--
Chris Hall
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Re: [patch] printf.3: correctly describe the meaning of a negative precision

[Michael Kerrisk (man-pages)]

On 09/02/13 16:41, Christopher Hall wrote:
> The printf(3) manpage says that a negative precision is taken to be
> zero, whereas printf(3p) says that a negative precision is taken as if
> the precision were omitted.  glibc agrees with the latter (posix)
> specification.
> 
> Test code:
> 
>     printf("%f\n",42.0);      // "42.000000"
>     printf("%.*f\n",0,42.0);  // "42"
>     printf("%.*f\n",-1,42.0); // "42.000000"
> 
> This patch corrects the explanation to match what actually happens.

Thanks for the thorough and clear report, Chris. Patch applied.

Cheers,

Michael


> diff --git i/man3/printf.3 w/man3/printf.3
> index f5e96d3..2c86bf1 100644
> --- i/man3/printf.3
> +++ w/man3/printf.3
> @@ -409,8 +409,9 @@ Instead of a decimal digit string one may write
> "*" or "*mquot;
>  is given in the next argument, or in the m-th argument, respectively,
>  which must be of type
>  .IR int .
> -If the precision is given as just \(aq.\(aq, or the precision is negative,
> -the precision is taken to be zero.
> +If the precision is given as just \(aq.\(aq, the precision is taken to
> +be zero.  A negative precision is taken as if the precision were
> +omitted.
>  This gives the minimum number of digits to appear for
>  .BR d ,
>  .BR i ,
> 
> 
> --
> Chris Hall
> 

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