Q: Is there a good way to overcome this apparent bug without modifying the
mfc code?
___________________________________
Info: Although it is NOT a good idea, I seemed to have perhaps located a
bug in this function with the GetLength call whose results are sent to the
sub-call to Concatenate. So I added the following and it asserts on
particular strings that are used. (I am not sure if this makes any
difference, but I am using class derived from CString that ends up calling
this code... However, that class never does anything remotely like touching
any private CString data without going through the very normal exposed
methods.)
Code as modified in CStringT.h file (line# 2013):
friend CStringT operator+( const CStringT& str1, const CStringT& str2 )
{
CStringT strResult( str1.GetManager() );
int str1_GetLength = str1.GetLength();
int str1_lstrlen = lstrlen(str1);
int str2_GetLength = str2.GetLength();
int str2_lstrlen = lstrlen(str2);
ASSERT ( str1_GetLength == str1_lstrlen );
ASSERT ( str2_GetLength == str2_lstrlen );
Concatenate( strResult, str1, str1.GetLength(), str2, str2.GetLength() );
return( strResult );
}
______________________________
Values are as follows as the debugger is about to eexecute the first ASSERT
statement:
str1 {0x0127a658 "<Message>"} const
ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > > &
str2 {0x0127a4a8 "chris logged off."}const
ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > > &
str1_GetLength 9 int
str1_lstrlen 9 int
str2_GetLength 18 int
str2_lstrlen 17 int
Ignore the assert and the result is:
strResult {0x0127a5a8 "<Message>chris logged off."}
ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > >
________________________________
Notice that in this instance, the second assert will fail. If I ignore it,
then then next time I enter this function on this string to concatenate more,
the str1 length is wrong and the concantenation writes the added string just
after the null so that the result is incorrect.
___________________________________
str1_GetLength 27 int
str1_lstrlen 26 int
str2_GetLength 2 int
str2_lstrlen 2 int
str1 {0x0127a5a8 "<Message>chris logged off."} const
ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > > &
str2 {0x0127a610 "</"} const
ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > > &
strResult {0x012525b8 "<Message>chris logged off."}
ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > >
_____________________________
Tony_Morris at Teledyne dot com 2 2158
The bug is probably in the construction of str2. Can you show us that code?
TonyM wrote: Q: Is there a good way to overcome this apparent bug without modifying the mfc code? ___________________________________
Info: Although it is NOT a good idea, I seemed to have perhaps located a bug in this function with the GetLength call whose results are sent to the sub-call to Concatenate. So I added the following and it asserts on particular strings that are used. (I am not sure if this makes any difference, but I am using class derived from CString that ends up calling this code... However, that class never does anything remotely like touching any private CString data without going through the very normal exposed methods.)
Code as modified in CStringT.h file (line# 2013): friend CStringT operator+( const CStringT& str1, const CStringT& str2 ) { CStringT strResult( str1.GetManager() );
int str1_GetLength = str1.GetLength(); int str1_lstrlen = lstrlen(str1); int str2_GetLength = str2.GetLength(); int str2_lstrlen = lstrlen(str2); ASSERT ( str1_GetLength == str1_lstrlen ); ASSERT ( str2_GetLength == str2_lstrlen );
Concatenate( strResult, str1, str1.GetLength(), str2, str2.GetLength() );
return( strResult ); } ______________________________ Values are as follows as the debugger is about to eexecute the first ASSERT statement:
str1 {0x0127a658 "<Message>"} const ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > > &
str2 {0x0127a4a8 "chris logged off."}const ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > > &
str1_GetLength 9 int
str1_lstrlen 9 int
str2_GetLength 18 int
str2_lstrlen 17 int
Ignore the assert and the result is: strResult {0x0127a5a8 "<Message>chris logged off."} ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > >
________________________________
Notice that in this instance, the second assert will fail. If I ignore it, then then next time I enter this function on this string to concatenate more, the str1 length is wrong and the concantenation writes the added string just after the null so that the result is incorrect.
___________________________________
str1_GetLength 27 int
str1_lstrlen 26 int
str2_GetLength 2 int
str2_lstrlen 2 int
str1 {0x0127a5a8 "<Message>chris logged off."} const ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > > &
str2 {0x0127a610 "</"} const ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > > &
strResult {0x012525b8 "<Message>chris logged off."} ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > > _____________________________
Tony_Morris at Teledyne dot com
Thanks Doug!
I am not sure why, but my single post to the "VC.ATL" group has been posted
here too...???
Anyhow, your question is a copy of the answer from that group: >>>>>>>>>>>>>>>>>>>>>>>>>>>
"doug mansell" wrote: The bug is probably in the construction of str2. Can you show us that code?>>>>>>>>>>>>>>>>>>>>>>>>>>>
Right on the mark! I had a transfer function that was doing a += into a
CString that ended up placing one extra NULL in the string. I would have
never guessed that CString would support additional NULLs in the data but
sure enough, the following has the output of incrementing the length even
though the string passed to lstrlen() returns 0 every time!
_____________________________________
CString str("");
TCHAR ch = '\0';
MessageBox(::GetActiveWindow(), "Length: " + CTekString(str.GetLength()) ,
"str.GetLength()", MB_OK);
MessageBox(::GetActiveWindow(), "Length: " + CTekString(lstrlen(str)) ,
"str.GetLength()", MB_OK);
str += ch;
MessageBox(::GetActiveWindow(), "Length: " + CTekString(str.GetLength()) ,
"str.GetLength()", MB_OK);
MessageBox(::GetActiveWindow(), "Length: " + CTekString(lstrlen(str)) ,
"str.GetLength()", MB_OK);
str += ch;
MessageBox(::GetActiveWindow(), "Length: " + CTekString(str.GetLength()) ,
"str.GetLength()", MB_OK);
MessageBox(::GetActiveWindow(), "Length: " + CTekString(lstrlen(str)) ,
"str.GetLength()", MB_OK);
________________________________________
Output:
0
0
1
0
2
0
__________________________________________________ _
Thank you profusely for the insight!!!
TonyM
"Igor Tandetnik" wrote:
"TonyM" <Tony_Morris @at Teledyne .dot com> wrote in message news:E0**********************************@microsof t.com Info: Although it is NOT a good idea, I seemed to have perhaps located a bug in this function with the GetLength call whose results are sent to the sub-call to Concatenate. So I added the following and it asserts on particular strings that are used. (I am not sure if this makes any difference, but I am using class derived from CString that ends up calling this code... However, that class never does anything remotely like touching any private CString data without going through the very normal exposed methods.)
Code as modified in CStringT.h file (line# 2013): friend CStringT operator+( const CStringT& str1, const CStringT& str2 ) { CStringT strResult( str1.GetManager() );
int str1_GetLength = str1.GetLength(); int str1_lstrlen = lstrlen(str1); int str2_GetLength = str2.GetLength(); int str2_lstrlen = lstrlen(str2); ASSERT ( str1_GetLength == str1_lstrlen ); ASSERT ( str2_GetLength == str2_lstrlen );
Concatenate( strResult, str1, str1.GetLength(), str2, str2.GetLength() );
return( strResult ); } ______________________________ Values are as follows as the debugger is about to eexecute the first ASSERT statement:
str1 {0x0127a658 "<Message>"} const ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > > &
str2 {0x0127a4a8 "chris logged off."}const ATL::CStringT<char,StrTraitMFC_DLL<char,ATL::ChTra itsCRT<char> > > &
str1_GetLength 9 int
str1_lstrlen 9 int
str2_GetLength 18 int
str2_lstrlen 17 int
CString supports embedded NULs in strings. In the presence of embedded NULs, GetLength differs from lstrlen. So the question is, how did you set up str2 so that it ended up with an extra NUL at the end? Show a complete program, where you set up the arguments and then invoke the operator. -- With best wishes, Igor Tandetnik
"On two occasions, I have been asked [by members of Parliament], 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able to rightly apprehend the kind of confusion of ideas that could provoke such a question." -- Charles Babbage This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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