.NET (Core and Framework)

30-Jan-09 23:33

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The need to optimize rises from a bad design.My articles[^]

Number formats

PIEBALDconsult30-Jan-09 16:16

30-Jan-09 16:16

I'm working on a utility that will allow the user to query some data from a database and output it.
I would like to support allowing the user to provide a format for the numbers, particularly if hexadecimal representation is desired.
Ideally I could simply do ((System.IFormattable) datarow [ columnname ]).ToString ( format , null ), but when hexadecimal is requested the user may (should) want to tack on a leading "0x" and I've been unable to form a format that will do that.

What should work is "'0x'X4", the '0x' should be copied to the output and then the value should be formatted with X4.

From the documentation:
"
'ABC' "ABC"
Literal string
Characters enclosed in single or double quotes are copied to the result string, and do not affect formatting.
"

Bull-pucky; they do affect formatting, they screw it up!

The closest I've gotten is string.Format ( format , datarow [ columnname ] ) with a format of "0x{0:X4}", but the user shouldn't need to specify the braces and such.

I'm considering using a Regular Expression and pre-processing the format to remove literal text before passing it to ToString, and concatenating the thing back together afterward.

I'm hoping someone here has a better solution.

Wendelius30-Jan-09 23:56

30-Jan-09 23:56

The format characters you use should be enclosed with {}. I think there's nothing you can do about it.

I think the main question is what kind of options do you want to offer to the user? For example if you want to use syntax like:

"Hex, 4"

That would be converted using something like the following (with proper checks for the syntax):

If (format.StartsWith("hex", StringComparison.InvariantCultureIgnoreCase)) {
   formatString = string.Format("0x{{0:X{0}}}", 
                                int.Parse(format.Substring(format.IndexOf(',') + 1)))
}

The need to optimize rises from a bad design.My articles[^]

PIEBALDconsult31-Jan-09 3:48

31-Jan-09 3:48

Mika Wendelius wrote:
enclosed with {}.

That's only with string.Format and its ilk. Which, as I said, works, but isn't ideal; the user would need to know too much about the internal workings of the program.

I could also just not support hex; after all, the database won't display the values that way.
I could also not allow a width specifier.
I could have hex and width specified separately.

On the other hand, this is just one simple utility; in the future I may have a project that really requires this.

I'd much prefer to use ToString and allow the user to specify "any valid Custom Numeric Format String[^]"

That should offer the greatest flexibility with the least intervention on my part. And it should work, according to the documentation.

I'll investigate my RegularExpression idea some time today. Thanks for your response.

Wendelius31-Jan-09 4:05

31-Jan-09 4:05

PIEBALDconsult wrote:
And it should work, according to the documentation

I'm pretty sure it works. Although I haven't used it so that the user gives the format, I read the format typically from database and it works fine.

PIEBALDconsult wrote:
I'll investigate my RegularExpression idea some time today

Possibly the best way to go.

PIEBALDconsult wrote:
Thanks for your response

No problem.

The need to optimize rises from a bad design.My articles[^]

PIEBALDconsult31-Jan-09 5:33

31-Jan-09 5:33

Mika Wendelius wrote:
I read the format typically from database

For this utility I'll get it via XML file, but the user who creates the file should be able to specify what he wants without knowing much about the internal plumbing.

An added bonus to how I envision ~~working around this problem~~ responding pro-actively to this opportunity is that I can allow multiple sub-formats in the format.
With string.Format I can use "{0:X4}={0}" to format the same value into the output twice, but ToString doesn't seem to support that on its own: 20.ToString ( "X4'='0" ) results in X4=20.
But if I pre-process the format, I can add support that I feel ToString should have; split the format into { "X4" , "'='" , "0" }, then iterate and if the sub-format is literal text, output it (Append to a StringBuilder), otherwise pass the sub-format to ToString and output the result.

The resultant process should then better match how I understand ToString should work with custom numeric formats.

Wendelius31-Jan-09 6:01

31-Jan-09 6:01

That sounds really good!

The need to optimize rises from a bad design.My articles[^]

PIEBALDconsult31-Jan-09 11:18

31-Jan-09 11:18

Well, that, was easy. I just don't think it's enough to form its own article.

20.ApplyFormat ( "'0x'X\"=\"0d" ) yields "0x14=20d"

Wendelius31-Jan-09 11:26

31-Jan-09 11:26

Seems easy, but a stupid question: What's ApplyFormat? It doesn't seem to be any .Net method for int.

The need to optimize rises from a bad design.My articles[^]

PIEBALDconsult31-Jan-09 11:28

31-Jan-09 11:28

Ah, see? Obfuscation. That's the Extension Method I just wrote.

Wendelius31-Jan-09 11:31

31-Jan-09 11:31

That's what I thought Smile | :)

Well, if the implementation is more than one line perhaps you should still consider the article Smile | :)

The need to optimize rises from a bad design.My articles[^]

PIEBALDconsult31-Jan-09 15:50

31-Jan-09 15:50

Yeah, I think I will.

But I've also been directed to Customizing Format Strings[^], so I'll look through that to see if it may be a better or complementary technique.

PIEBALDconsult1-Feb-09 16:39