[Qt-interest] Problems With tr and operator <<

[Thiago Macieira]

Em Segunda-feira 15. Março 2010, às 05.04.17, Aaron Lewis escreveu:
> Sorry for sending this mail to all these address. ;-)
> 
> Hi , I was reading your book , Qt/C++ Advance Programming.
> Part 12.5 , you write a image converter
> 
> I rewrited this program , and add some new functions
> 
> -snip-
> 
>         if(ui->colorBox->isChecked())
>           //  arg << tr("-depth
> %1").arg(ui->colorComboBox->currentText());   //fails  , convert doesn't
> recognize '-depth 32'
>             arg << "-depth" << ui->colorComboBox->currentText();   //
> works , don't know why
> 
> -snip-
> 
> Fist method doesn't work , while the second works , convert program
> tells me '-depth 32' is not recognized.
> Is there any differences between `tr' and operator `<<' ?

Yes, they are not at all the same thing.

For those of us without the book, we are without context. We don't know what 
arg is, so we don't know what operator<< you're talking about.

I am going to guess it's a QStringList, used to hold the arguments to 
QProcess. If I am guessing right, then operator<< is the same as 
QList::append. So note the difference:

Case 1:
	arg.append("-depth 32");
Case 2:
	arg.append("-depth");
	arg.append("32");

One creates one argument that includes a space. The other creates two 
arguments.

Also note how it makes no sense to translate "-depth" to another language, 
since convert cannot understand anything other than "-depth".

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Senior Product Manager - Nokia, Qt Development Frameworks
      PGP/GPG: 0x6EF45358; fingerprint:
      E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4 5358
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