Bug? Error parsing string "-0" to float

[emexes]

This code (2 lines of diagnosis hacks + 1 original problem line):

Dim TempString As String = lblReading.Text
Log("len = " & TempString.Length & ", str = [" & TempString & "] isnum = " & IsNumber(TempString))
       
Dim CurrentReading As Float = TempString    '''lblReading.Text

is producing this error when the string is "-0":

len = 2, str = [-0] isnum = true
Error occurred on line: 423 (Main)
Cannot parse: -0
Stack Trace: (
CoreFoundation <redacted> + 252
libobjc.A.dylib objc_exception_throw + 56
CoreFoundation <redacted> + 0
PTOC -[B4I ObjectToNumber:] + 464
PTOC -[B4IRDebugUtils numberCast::] + 268
CoreFoundation <redacted> + 144
CoreFoundation <redacted> + 292
PTOC +[B4I runDynamicMethod:method:throwErrorIfMissing:args:] + 1624
PTOC -[B4IShell runMethod:] + 448
PTOC -[B4IShell raiseEventImpl:method:args::] + 1640
PTOC -[B4IShellBI raiseEvent:eventarams:] + 1372
PTOC __24-[B4ITimer startTicking]_block_invoke + 332
libdispatch.dylib <redacted> + 16
libdispatch.dylib <redacted> + 412
libdispatch.dylib <redacted> + 1308
libdispatch.dylib <redacted> + 784
CoreFoundation <redacted> + 12
CoreFoundation <redacted> + 1924
CoreFoundation CFRunLoopRunSpecific + 436
GraphicsServices GSEventRunModal + 104
UIKitCore UIApplicationMain + 212
PTOC main + 124
libdyld.dylib <redacted> + 4
)

I tried some parsing test code at the start of the same program:

Private Sub Application_Start (Nav As NavigationController)
   
    'SetDebugAutoFlushLogs(True) 'Uncomment if program crashes before all logs are printed.
   
    Dim TestString As String
    Dim TestFloat As Float
   
    TestString = "1.23"
    TestFloat = TestString
    Log(TestString & " = " & TestFloat)

    TestString = "-1.23"
    TestFloat = TestString
    Log(TestString & " = " & TestFloat)

    TestString = "0"
    TestFloat = TestString
    Log(TestString & " = " & TestFloat)

    TestString = "+0"
    TestFloat = TestString
    Log(TestString & " = " & TestFloat)
   
    TestString = "-0"
    TestFloat = TestString
    Log(TestString & " = " & TestFloat)

but it seems to work just fine on the offending "-0" (indeed: better than fine, since it looks like it implements the IEEE signed-zero nuance):

Application_Start
1.23 = 1.2300000190734863
-1.23 = -1.2300000190734863
0 = 0
+0 = 0
-0 = -0
Application_Active

Having mentioned the signed-zero nuance, perhaps I should tug on that loose thread a little harder.

But still, why would the same casting work in one case, fail in another? Especially when IsNumber says the string is ok.

 

[emexes]

I added some more diagnosis code, thinking that perhaps the string that looks like "-0" is actually some other Unicode characters that just look like "-" and "0" but are actually some other character that just looks similar:

Dim TempString As String = lblReading.Text
Log("len = " & TempString.Length & ", str = [" & TempString & "] isnum = " & IsNumber(TempString))

Dim TempNegativeZero As String = "-0"
Log(TempString.CompareTo(TempNegativeZero))

Dim TempFloat As Float = TempNegativeZero
Log(TempNegativeZero & " = " & TempFloat)
Log((TempFloat * 100) & " " & (TempFloat + 100))

Dim CurrentReading As Float = TempString    '''lblReading.Text

but I still get the same error... even though the TempString and TempNegativeZero strings are identical (CompareTo = 0), and the assignment statements to local floats look identical, one parses ok and the other doesn't:

len = 2, str = [-0] isnum = true
0
-0 = -0
-0 100
Error occurred on line: 430 (Main)
Cannot parse: -0
Stack Trace: (
CoreFoundation <redacted> + 252
libobjc.A.dylib objc_exception_throw + 56
CoreFoundation <redacted> + 0
PTOC -[B4I ObjectToNumber:] + 464
PTOC -[B4IRDebugUtils numberCast::] + 268
CoreFoundation <redacted> + 144
CoreFoundation <redacted> + 292
PTOC +[B4I runDynamicMethod:method:throwErrorIfMissing:args:] + 1624
PTOC -[B4IShell runMethod:] + 448
PTOC -[B4IShell raiseEventImpl:method:args::] + 1640
PTOC -[B4IShellBI raiseEvent:eventarams:] + 1372
PTOC __24-[B4ITimer startTicking]_block_invoke + 332
libdispatch.dylib <redacted> + 16
libdispatch.dylib <redacted> + 412
libdispatch.dylib <redacted> + 1308
libdispatch.dylib <redacted> + 784
CoreFoundation <redacted> + 12
CoreFoundation <redacted> + 1924
CoreFoundation CFRunLoopRunSpecific + 436
GraphicsServices GSEventRunModal + 104
UIKitCore UIApplicationMain + 212
PTOC main + 124
libdyld.dylib <redacted> + 4
)

 

[emexes]

The generated code from B4I looks the same for both cases:

@implementation ResumableSub_main_tmrBluetooth_Tick {
b4i_main* parent;
long long _t;
float _r;
float _g;
float _b;
NSString* _tempstring;
NSString* _tempnegativezero;
float _tempfloat;
float _currentreading;
int _bubbleleftmin;
int _bubbleleftmax;
float _x;
}

B4IRDebugUtils.currentLine=983119;
 //BA.debugLineNum = 983119;BA.debugLine="Dim TempFloat As Float = TempNegativeZero";
_tempfloat = [self.bi ObjectToNumber:_tempnegativezero].floatValue;
...
B4IRDebugUtils.currentLine=983123;
 //BA.debugLineNum = 983123;BA.debugLine="Dim CurrentReading As Float = TempString    '''l";
_currentreading = [self.bi ObjectToNumber:_tempstring].floatValue;

so for the time being, I will just put it down to being one of life's little mysteries, and work around it.

 

[emexes]

Continued on my merry way, then - after several successful runs - got this:

Application_Start
1.23 = 1.23
-1.23 = -1.23
0 = 0
Error occurred on line: 98 (Main)
Cannot parse: +0
Stack Trace: (
CoreFoundation <redacted> + 252
libobjc.A.dylib objc_exception_throw + 56
CoreFoundation <redacted> + 0
PTOC -[B4I ObjectToNumber:] + 464
PTOC -[ResumableSub_main_Application_Start resume::] + 2872
...

ie from this test case:

unchanged from the previous runs.

 

[Cableguy]

The IDE automatically cast string to numerical values...
I'm guessing the issue is the plus sign...
The IDE may see it as an arithmetic function rather than a positive number, since the lack of minus sign automatically define the positiveness of the number.

 

[Erel]

It is related to an internal check that is required for parsing zeros, that tries to distinguish between valid and invalid inputs.

 

[emexes]

Re: the +0

The oddity was that it worked fine, then randomly stopped working.

I agree that many BASICs choke on leading-but-needless "+" signs. It's nice when it works, though, for things like polynomial coefficients, to emphasize that you haven't forgotten the sign.

I've done as much diagnosis as I can afford timewise right now, but just wanted to document it in case somebody else hits the same issue, so's they know they're not alone ;-)

The "-0" is the result of NumberFormat2(-0.123, 1, 0, 0, False).

 

[emexes]

I have narrowed the issue down slightly, and possibly added some mystery too: the error occurs when the "-0" string is from a TextField or Label, but not when it is from a string literal.

Two seemingly identical Strings, both "-0", one parses with no error, the other causes an error. Regardless of the order in which they are done, the "F = InputString" line fails with "Cannot parse: -0"

I am using B4I 5.30, with iOS 12.2 on an iPhone 5S.

Starting from a blank new project, I can reproduce the error reliably with:

Private Sub Application_Start (Nav As NavigationController)
    'SetDebugAutoFlushLogs(True) 'Uncomment if program crashes before all logs are printed.
    NavControl = Nav
    Page1.Initialize("Page1")
    Page1.Title = "Page 1"
    Page1.RootPanel.Color = Colors.White
    NavControl.ShowPage(Page1)
   
    Dim LiteralString As String
    Dim InputString As String
   
    Dim F As Float '''Double
       
    LiteralString = "-0"

    Dim TF As TextField
    TF.Initialize("TF")
    TF.Text = LiteralString ''' "-0"
    InputString = TF.Text
   
    Log(LiteralString.Length & " [" & LiteralString & "] " & IsNumber(LiteralString))
    Log(InputString.Length & " [" & InputString & "] " & IsNumber(InputString))
    Log(LiteralString.CompareTo(InputString))
       
    F = LiteralString
    Log("LiteralString " & F)
   
    F = InputString
    Log("InputString " & F)
   
End Sub

which logs the following error (after both IsNumbers return True, and Compare indicates strings are identical?):

Application_Start
2 [-0] true
2 [-0] true
0
LiteralString -0
Error occurred on line: 49 (Main)
Cannot parse: -0
Stack Trace: (
CoreFoundation <redacted> + 252
libobjc.A.dylib objc_exception_throw + 56
CoreFoundation <redacted> + 0
B4i Example -[B4I ObjectToNumber:] + 464
B4i Example -[B4IRDebugUtils numberCast::] + 268
CoreFoundation <redacted> + 144
CoreFoundation <redacted> + 292
B4i Example +[B4I runDynamicMethod:method:throwErrorIfMissing:args:] + 1624
B4i Example -[B4IShell runMethod:] + 448
B4i Example -[B4IShell raiseEventImpl:method:args::] + 1640
B4i Example -[B4IShellBI raiseEvent:eventarams:] + 1372
B4i Example __33-[B4I raiseUIEvent:eventarams:]_block_invoke + 60
libdispatch.dylib <redacted> + 24
libdispatch.dylib <redacted> + 16
libdispatch.dylib <redacted> + 1068
CoreFoundation <redacted> + 12
CoreFoundation <redacted> + 1924
CoreFoundation CFRunLoopRunSpecific + 436
GraphicsServices GSEventRunModal + 104
UIKitCore UIApplicationMain + 212
B4i Example main + 124
libdyld.dylib <redacted> + 4
)
Application_Active

where line 49 is the "F = InputString" string-to-float conversion:

It has me stumped. Why would the memory location of the string make a difference to the parsing? Is there some protection mechanism kicking in, like the string-to-float parsing routine doesn't have access to the string data held inside TextField that is possibly still pointed to by the InputString string variable? I tried to force construction of a brand new string, by adding spaces and then Trimming it, but the error seems quite resilient.

My main worry is that IsNumber returns True on a string that generates a parsing error. I don't know how easy this is to fix, other than a simple filter for "-0" (and "-0.0" and "-0.000E+00" and...) vs what are the chances of somebody entering "-0" anyway ?

 

[emexes]

Hmm. The Trim function also "pollutes" the string, so it isn't just strings that have come from within views, eg:

Private Sub Application_Start (Nav As NavigationController)
    'SetDebugAutoFlushLogs(True) 'Uncomment if program crashes before all logs are printed.
    NavControl = Nav
    Page1.Initialize("Page1")
    Page1.Title = "Page 1"
    Page1.RootPanel.Color = Colors.White
    NavControl.ShowPage(Page1)
   
    Dim S As String
    Dim F As Float '''Double
       
    S = "-0"
    Log(S.Length & " [" & S & "] " & IsNumber(S))
   
    F = S
    Log(F)
   
    S = S.Trim    ''' "-0".Trim
    Log(S.Length & " [" & S & "] " & IsNumber(S))
   
    F = S    '''.Trim
    Log(F)
   
End Sub

results in:

Application_Start
2 [-0] true
-0
2 [-0] true
Error occurred on line: 42 (Main)
Cannot parse: -0
Stack Trace: (
CoreFoundation <redacted> + 252
libobjc.A.dylib objc_exception_throw + 56
CoreFoundation <redacted> + 0
B4i Example -[B4I ObjectToNumber:] + 464
B4i Example -[B4IRDebugUtils numberCast::] + 268
CoreFoundation <redacted> + 144
CoreFoundation <redacted> + 292
B4i Example +[B4I runDynamicMethod:method:throwErrorIfMissing:args:] + 1624
B4i Example -[B4IShell runMethod:] + 448
B4i Example -[B4IShell raiseEventImpl:method:args::] + 1640
B4i Example -[B4IShellBI raiseEvent:eventarams:] + 1372
B4i Example __33-[B4I raiseUIEvent:eventarams:]_block_invoke + 60
libdispatch.dylib <redacted> + 24
libdispatch.dylib <redacted> + 16
libdispatch.dylib <redacted> + 1068
CoreFoundation <redacted> + 12
CoreFoundation <redacted> + 1924
CoreFoundation CFRunLoopRunSpecific + 436
GraphicsServices GSEventRunModal + 104
UIKitCore UIApplicationMain + 212
B4i Example main + 124
libdyld.dylib <redacted> + 4
)
Application_Active

where line 42 is the string-to-float conversion of the same variable S (albeit just trimmed, with no apparent effect):

 

[Erel]

My main worry is that IsNumber returns True on a string that generates a parsing error.

I agree and I've changed IsNumber behavior to return False in this case.

 

[emexes]

I agree and I've changed IsNumber behavior to return False in this case.

Well, that'll fix it, I guess. I'm sad that I will no longer experience the thrill of seeing negative zero (sometimes) handled distinctly per IEEE, though ;-/

I trust non-zeroes like "-0.0123" will still be ok. Also, "-0.0E+01" generated an error, even though it has a non-zero digit in it.