Hello,

I am running the following code segment in visual studio 2005.

size_t cchSize = 10*sizeof(TCHAR);
LPTSTR temp = (LPTSTR)malloc(cchSize);
temp[0] = '\0';
_tcscat_s(temp, cchSize, _T("hello"));
free(temp);

It fails at the statement -

free(temp)

with the error:

Heap block at 00A57F80 modified at 00A57FC0 past requested size of 38.

If i change _tcscat_s to deprecated _tcscat there is no error. Can
anyone throw some light on this?


Thanks,
C++Programmer.

drazbliz@yahoo.com wrote:[color=blue]
> Hello,
>
> I am running the following code segment in visual studio 2005.
>
> size_t cchSize = 10*sizeof(TCHAR);
> LPTSTR temp = (LPTSTR)malloc(cchSize);
> temp[0] = '\0';
> _tcscat_s(temp, cchSize, _T("hello"));
> free(temp);
>
> It fails at the statement -
>
> free(temp)
>
> with the error:
>
> Heap block at 00A57F80 modified at 00A57FC0 past requested size of 38.
>
> If i change _tcscat_s to deprecated _tcscat there is no error. Can
> anyone throw some light on this?[/color]

Not really, those functions starting with an underscore do not exist in
C++ and I have no idea what they do. Perhaps you should ask in a
newsgroup where those functions are topical, perhaps one with microsoft
and windows in the name.

Ben Pope
--
I'm not just a number. To many, I'm known as a string...

In article <1143541635.951736.314680@e56g2000cwe.googlegroups .com>,
"drazbliz@yahoo.com" <drazbliz@yahoo.com> wrote:
[color=blue]
> Hello,
>
> I am running the following code segment in visual studio 2005.
>
> size_t cchSize = 10*sizeof(TCHAR);
> LPTSTR temp = (LPTSTR)malloc(cchSize);
> temp[0] = '\0';
> _tcscat_s(temp, cchSize, _T("hello"));
> free(temp);
>
> It fails at the statement -
>
> free(temp)
>
> with the error:
>
> Heap block at 00A57F80 modified at 00A57FC0 past requested size of 38.
>
> If i change _tcscat_s to deprecated _tcscat there is no error. Can
> anyone throw some light on this?[/color]

I believe that if you put the above code in a main all by itself, the
error will go away as well. If not, then probably _tcscat_s doesn't do
what you think it does and is writing past the requested size.

I can't help but wonder how big a TCHAR is if 10 * sizeof(TCHAR) ends up
equaling 38...


--
Magic depends on tradition and belief. It does not welcome observation,
nor does it profit by experiment. On the other hand, science is based
on experience; it is open to correction by observation and experiment.

drazbliz wrote:
[color=blue]
> I am running the following code segment in visual studio 2005.
>
> size_t cchSize = 10*sizeof(TCHAR);
> LPTSTR temp = (LPTSTR)malloc(cchSize);
> temp[0] = '\0';
> _tcscat_s(temp, cchSize, _T("hello"));
> free(temp);[/color]

Why on Earth are you not using a CString, a CStringW, or a _bstr_t?

And why are you using a strcat() derived method when you could use a
strcpy() derived method, or even a _tcsdup()?

And why malloc() in a C++ program?

--
Phlip
http://www.greencheese.org/ZeekLand <-- NOT a blog!!!

[dswallow]

Originally Posted by drazbliz@yahoo.com

Hello,

I am running the following code segment in visual studio 2005.

size_t cchSize = 10*sizeof(TCHAR);
LPTSTR temp = (LPTSTR)malloc(cchSize);
temp[0] = '\0';
_tcscat_s(temp, cchSize, _T("hello"));
free(temp);

It fails at the statement -

free(temp)

with the error:

Heap block at 00A57F80 modified at 00A57FC0 past requested size of 38.

If i change _tcscat_s to deprecated _tcscat there is no error. Can
anyone throw some light on this?

_tcscat_s (and most if not all the secure runtime functions) uses the # of characters as the buffer size, not the # of bytes. You're probably compiling using the Unicode character set, so a TCHAR is 2 bytes, not 1.

The debug version of these functions also write to the entire buffer area, so by telling it there's 20 characters (40 bytes), the _tcscat_s function ends up overwriting memory beyond the allocated 10 characters (20 bytes), which leaves the heap damaged.


Try:

size_t cchSize = 10;
LPTSTR temp = (LPTSTR)malloc(cchSize*sizeof(TCHAR));
temp[0] = '\0';
_tcscat_s(temp, cchSize, _T("hello"));
free(temp);