[ wxwindows-Bugs-1432568 ] wxDataInputStream::ReadDouble and Write

[SourceForge.net]

Bugs item #1432568, was opened at 2006-02-16 03:18
Message generated for change (Comment added) made by axcn
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=109863&aid=1432568&group_id=9863

Please note that this message will contain a full copy of the comment thread,
including the initial issue submission, for this request,
not just the latest update.
Category: Common
Group: Trivial
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Cristiano (cavila)
Assigned to: Nobody/Anonymous (nobody)
Summary: wxDataInputStream::ReadDouble and Write

Initial Comment:
I'm using wxWidgets 2.6.2, wxMSW port compiled through
ming342 compiler. I use the dev-cpp editor often.

When I started using wxDataInputStream class found
errors on reading double data.

I checked the source code and found the following:

// Must be at global scope for VC++ 5
extern "C" void ConvertToIeeeExtended(double num,
unsigned char *bytes);

// Must be at global scope for VC++ 5
extern "C" double ConvertFromIeeeExtended(const
unsigned char *bytes);

double wxDataInputStream::ReadDouble()
{
#if wxUSE_APPLE_IEEE
  char buf[10];

  m_input->Read(buf, 10);
  return ConvertFromIeeeExtended((unsigned char *)buf);
#else
  return 0.0;
#endif
}

void wxDataOutputStream::WriteDouble(double d)
{
  char buf[10];

#if wxUSE_APPLE_IEEE
  ConvertToIeeeExtended(d, (unsigned char *)buf);
#else
#if !defined(__VMS__) && !defined(__GNUG__)
# pragma warning "wxDataOutputStream::WriteDouble() not
using IeeeExtended - will not work!"
#endif
   buf[0] = '\0';
#endif
  m_output->Write(buf, 10);
}

This is trying to read 10bytes of binary data from the
file as double. The double value for the compiler is 8
bytes long. I don't checked if wxUSE_APPLE_IEEE is 
defined and the function is always returning 0.0 .
Making a check on file size before and after the read a
found a 10byte difference, so this symbol may be defined.

A possible solution is to define a compiler check for
sizeof(double) and read the write quantity of data from
file.

----------------------------------------------------------------------

Comment By: Dmitry Krayushkin (axcn)
Date: 2008-03-04 08:55

Message:
Logged In: YES 
user_id=2026574
Originator: NO

Yes. I found this bug too.
This is my report of bug:

wxDataInputStraem::ReadDouble() not worked?

I test it under wxMSW (MinGW compiler) and wxGTK 2.8.9
See comments in code.

C++ code:

double test_double[2] = {0.0001, 0.0002};
wxUint64 test_uint64;
wxMemoryInputStream mem((char*)&test_double, 2 * sizeof(double));
wxDataInputStream data_stream(mem);

//bad read
//with ReadDouble() we get "0" and 10 byte offset with wxMSW and 0 byte
with wxGTK after 1 ReadDouble() read!
wxMessageDialog(NULL, wxString(wxT("Readed: "))<< data_stream.ReadDouble()
<< wxString(wxT("\nOffset after 1 ReadDouble() read: ")) <<
mem.TellI()).Show(true);

//now return to begin and try again with Read64()
//Read64() show "0.0001" with 8 byte offset. All right here.
mem.SeekI(0);
test_uint64 = data_stream.Read64(); 
wxMessageDialog(NULL, wxString(wxT("Readed with Read64(): ")) <<
*((double*)&test_uint64) << wxString(wxT("\nOffset after 1 Read64() read:
")) << mem.TellI()).Show(true);


----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=109863&aid=1432568&group_id=9863