[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 :)