[Solved] sprintf in qt

[prabhuraj]

Hi all,
I have been working on a code whare in I have use sprintf in Qt. When use the sprintf function in the following way

@
QString ::sprintf(wr_buff, "%s",tr_buff); //tr_buff contains a string and I want to put it into wr_buff
@

I get following error

@
error: no matching function for call to ‘QString::sprintf(QString&, const char [42], QString&).
@

The requirement of application is such that I have to use sprint and nothing else.

Please help me rectify this problem.

Thanks

[andre]

According to the documentation, QString::sprintf has the format as the first argument, not as the second one.

[Alicemirror]

Hi,

I think that you should see on the Qt documentation for the api that create formatted strings. There are specific and complete functions / options for any kind of formatting reflecting the same options of sprintf.

[Franzk]

QString::sprintf is not a static function. It alters the QString object. The correct way of using it is therefore:

@QString str;
// ...
str.sprintf("%s", tr_buff);@

or

@QString str = QString().sprintf("%s", tr_buff);@

However if tr_buff is a QString already (which the error suggests), just use
@QString str = tr_buff;@

[giesbert]

aditionally, sprintf is not a static member function.

@
QString wr_buff;
char* tr_buff = "XXX";
wr_buff.sprintf("%s",tr_buff);
@

But you should take care:

bq. Warning: We do not recommend using QString::sprintf() in new Qt code. Instead, consider using QTextStream or arg(), both of which support Unicode strings seamlessly and are type-safe.

"see documentation of QString::sprintf":http://doc.qt.nokia.com/4.7/qstring.html#sprintf

If the requirement is to use sprint, are you sure, you shall do it with Qt? From my POV, it makes no sense, sorry...

EDIT: too slow..., Gerolf

[Franzk]

[quote author="Gerolf" date="1316155835"]If the requirement is to use sprint, are you sure, you shall do it with Qt? From my POV, it makes no sense, sorry...[/quote]I've come across some cases where you might want to use sprintf (e.g. formatted double precision numbers: %3.8lf is not possible with QString::arg(), but sometimes desirable). The problem OP shows isn't one of them.

[Alicemirror]

Btw, developing with Qt I think that the best practice is to use as possible the wide variety of api. At lest because grant one of the higher constan behavior on different platforms I have even see.

[prabhuraj]

Hey thanks a lot for all the replies. I finally got it working.
Thanks once again.

[Alicemirror]

Very good. Ifthe problem is solved plese set your first post title with [Solved] in front. Thank you.

[goetz]

[quote author="Franzk" date="1316155969"]I've come across some cases where you might want to use sprintf (e.g. formatted double precision numbers: %3.8lf is not possible with QString::arg(), but sometimes desirable). The problem OP shows isn't one of them.
[/quote]

This works for me:

@
double x = 42.23;
QString xStr = QString("%1").arg(x, 3, 'f', 8);
@

Although the 3 in 3.8lf is superfluous, as the field width is 10 at least (the dot, eight digits after the dot and at least one digit before the dot).

[Franzk]

Ah nice. In that case sprintf can be avoided.

[Alicemirror]

@Volker: prfectly agree with you. In Qt there are a lot of possibilities so a downgrade using sprintf is to be avoided at all. I don't use it by the middle of years '90 :)