writefln of strings array with size formatting

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bearophile_hugs reported this on 2012-01-21T15:28:00Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=7341

CC List

• andrei (@andralex)
• hsteoh
• lovelydear
• smjg

Description

D2 code:

import std.stdio;
void main() {
    int[] a1 = [1, 10, 5];
    writefln("%12d", a1);
    string[] a2 = ["red", "yellow", "ya"];
    writefln("%12s", a2);
}



Output:
[           1,           10,            5]
["red", "yellow", "ya"]



But I expect an output more like:
[           1,           10,            5]
[       "red",     "yellow",         "ya"]

[dlangBugzillaToGithub]

lovelydear commented on 2012-04-21T05:12:33Z

Was writefln supposed to work or arrays ? Here is what I get on 2.059:

PS E:\DigitalMars\dmd2\samples> rdmd bug.d
object.Exception@E:\DigitalMars\dmd2\windows\bin\..\..\src\phobos\std\format.d(1886): Incorrect format specifier for range: %d

[dlangBugzillaToGithub]

k.hara.pg commented on 2012-04-21T06:26:55Z

(In reply to comment #0)
> D2 code:
> 
> import std.stdio;
> void main() {
>     int[] a1 = [1, 10, 5];
>     writefln("%12d", a1);
>     string[] a2 = ["red", "yellow", "ya"];
>     writefln("%12s", a2);
> }
> 
> Output:
> [           1,           10,            5]
> ["red", "yellow", "ya"]
> 
> But I expect an output more like:
> [           1,           10,            5]
> [       "red",     "yellow",         "ya"]

If you want to give format specifier for elements explicitly, you should use compound format specifier (It is %( and %).)

    writefln("[%(%12d, %)]", [1, 10, 5]);
    writefln("[%(%12s, %)]", ["red", "yellow", "ya"]);

But, this code output:
[           1,           10,            5]
["red", "yellow", "ya"]

Because, string elements and character elements are treated specially. They are quoted, and other specifications are ignored.

https://github.com/D-Programming-Language/phobos/blob/master/std/format.d#L1930

But, I agree it is debatable thing.

[dlangBugzillaToGithub]

smjg commented on 2012-04-21T08:48:54Z

The reason for the original behaviour seems to be that the width specified for %s is taken to be the width to which the whole argument is formatted, not the width to which each element of the array is formatted.

But I'm getting the same error as SomeDude (DMD 2.059, Win32).  Kenji - what setup do you have that's giving a different result?

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lovelydear commented on 2012-04-21T12:07:22Z

(In reply to comment #3)
> But I'm getting the same error as SomeDude (DMD 2.059, Win32).  Kenji - what
> setup do you have that's giving a different result?

He wrote it. The code that's supposed to work is:

import std.stdio;
void main() {
    writefln("[%(%12d, %)]", [1, 10, 5]);
    writefln("[%(%12s, %)]", ["red", "yellow", "ya"]);
}

Not the original test example.

[dlangBugzillaToGithub]

bugzilla (@WalterBright) commented on 2019-12-12T12:06:48Z

*** Issue 9592 has been marked as a duplicate of this issue. ***