Truncating precision of type double for GUI variables.

[BruceV 0]

I would appreciate some advice on how to do the following. It seemed trivial, but I quickly got tangled up with the various formats for wide strings, a lot of the Embarcadero information turned out to be for Pascal, I’m working with C++ builder. And there are a number of different wide string formats.

 

I am displaying double values on the canvas, the following obviously works fine:

Label1 -> Caption = DoubleVal  ;

 

But I got into trouble when I wanted to constrain the display precision, there doesn’t appear to be a setting for the display object and just truncating the field width would be visually unappealing. So I applied the setprecision function with a stringstream output…..

 

ostringstream oss ;

oss << setprecision (4) << DoubleVal;  // This works

 

 How do I go from the stringstream to the GUI? Or is there a more direct approach?

[oliwe 6]

You could use:

Label1->Caption = oss.str().c_str();

[Remy Lebeau 1330]

Alternatively, have a look at Sysutils::Format()

 

Label1->Caption = Format(_D("%0.4f"), ARRAYOFCONST((DoubleVal)));

 

or (Ansi|Unicode)String::sprintf() 

 

Label1->Caption = String().sprintf(_D("%0.4f"), DoubleVal);

Edited June 3 by Remy Lebeau

[hansw 1]

You could also use FloatToStrF() which returns a UnicodeString using the local decimal separator.

In case you want get a double value from an input text, you could use TryStrToFloat() which returns TRUE if the input is a valid floating point number (which avoids an exception in case the input text is invalid).

[Remy Lebeau 1330]

7 hours ago, hansw said:

You could also use FloatToStrF() which returns a UnicodeString using the local decimal separator.

Oh yeah, I keep forgetting about that one.

 

Label1->Caption = FloatToStrF(DoubleVal, ffFixed, 10, 4);

 

There is also FormatFloat():

 

Label1->Caption = FormatFloat(_D("0.0000"), DoubleVal);