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stream bytes

 
 
Christopher
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Posts: n/a
 
      12-05-2011
I am trying to debug some code that supposedly stores text as bytes
and then back again.
The first step is to examine the contents.

Somewhere data was inserted that contained at least one character with
the signed bit set.
So, the supposed "text" isn't even valid text at all.

I had orginally written this code, which threw if an invalid text
cahr (or non-ascii) was found:

std::wstring StringBufferList::GetBytesAsText() const
{
// This class should have been storing bytes as unsigned char
rather than char
// to begin with and needs to be changed later.
//
// I am just adding this method quickly for debugging purposes.
//
// Because of the lack of type safety currently in insertion of
any type using a reinterpret_cast
// this class made use of, we must check each byte for validity.
//
// It was assumed only ascii characters would be used, but that
might not be the case

std::wstringstream output;
size_t numBytes = getSize();

for( const_iterator itBuffer = begin(); itBuffer != end(); itBuffer
++ )
{
for( size_t byteIndex = 0; byteIndex < numBytes; ++byteIndex )
{
char & data = itBuffer->buffer->value_.get()[byteIndex];

if( data < 0 )
{
// Error - Invalid byte value
std::wstringstream msg;
msg << L"Attempted to convert byte values to wide
character hex text values and came across a negative signed
character.";

LOG4CXX_ERROR(logger, msg.str());
throw InternalErrorException(__WFILE__, __LINE__) <<
msg.str();
}

output << std::hex << std::setw(2) << std::setfill(L'0')
<< data;
output << "' '";
}
}

return output.str();
}


In debugging, my exception happened.
Can I examine the values just by taking my if statement out? How do I
recognize the signed values in hex?

If this buffer supposedly held XML in ASCII, how would you go about
looking at the contents to see where it became invalid?



 
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Juha Nieminen
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Posts: n/a
 
      12-05-2011
Christopher <(E-Mail Removed)> wrote:
> In debugging, my exception happened.
> Can I examine the values just by taking my if statement out? How do I
> recognize the signed values in hex?


I don't really understand what is it that you are asking. Or, more
precisely, it sounds to me like you are asking how to add debug output
to your code, which is such a trivial question that I must have
misunderstood.
 
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Christopher
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Posts: n/a
 
      12-06-2011
Ok, maybe I should reword things.

Someone, sometime, made an erroneous buffer class. The intention the
author had was to store UTF-8 encoded text and that text was expected
to be XML. Instead, the author decided that all he had to do was
reinterpret_cast<const char *> whatever parameter came in to be
stored:

template <typename T, size_t L>
StringBufferList & operator << (const T (& value)[L])
{
append(reinterpret_cast<const char *>(&value), (L - 1) *
sizeof(T));
return *this;
}

Then when extracting he reinterpet_cast<const wchar_t *>
The author obviously had no idea what he was doing.

Later down the road, someone must have inserted something besides
UTF-8 encoded text. My goal is to identify where that is occuring. My
thought was to examine the contents of the buffer and see what parts
are able to be converted to UTF-8 encoded text, look at it, and see if
it is something recognizable, so as to give me a clue where the bad
insertions are occuring.

It isn't as easy as just setting a breakpoint and looking at the call
stack, because there is not much of a call stack, since the author
also decided to use boost::bind to trigger this via callbacks.

In order to examine the contents, since there is no telling what they
are, I thought I should dump it out to a file as a textual
representation of the bytes.

So my questions are
How do I dump the contents out as a textual representation of the
bytes? Would the code below do the trick?


std::wstring StringBufferList::GetBytesAsText() const
{
// This class should have been storing bytes as unsigned char
rather than char
// to begin with and needs to be changed later.
//
// I am just adding this method quickly for debugging purposes.
//
// Because of the lack of type safety currently in insertion of
any type using a reinterpret_cast
// this class made use of, we must check each byte for validity.

std::wstringstream output;
size_t numBytes = getSize();

for( const_iterator itBuffer = begin(); itBuffer != end(); itBuffer
++ )
{
for( size_t byteIndex = 0; byteIndex < numBytes; ++byteIndex )
{
int & byte = static_cast<int>(itBuffer->buffer-
>value_.get()[byteIndex]);

output << std::hex << std::setw(2) << std::setfill(L'0')
<< byte;
output << "' '";
}
}

return output.str();
}



I cannot simply examine things in the debugger, because
1) The enitre contents aren't valid text in any encoding, due to the
author's bug
2) The contents are split up amongst several data structures in a link
list







 
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