Re: C++ std::string tries to free() a not allocated pointer ?
Re: C++ std::string tries to free() a not allocated pointer ?
- Subject: Re: C++ std::string tries to free() a not allocated pointer ?
- From: Howard Moon <email@hidden>
- Date: Thu, 19 Nov 2009 08:09:39 -0800
On Nov 18, 2009, at 10:06 AM, Jean-Denis Muys wrote:
3- a buffer is allocated with 23 bytes in the library, form which a
SQLString is constructed.
The calling sequence I stepped through in the library is:
buffer = new char[23];
buffer[0] = 0;
length = 0;
return SQLString(buffer, length);
4- that return statement constructs a temporary SQLString through
that call chain:
#0 0x99056cb4 in std::string::_S_construct<char const*> ()
#1 0x99056d85 in std::basic_string<char, std::char_traits<char>,
std::allocator<char> >::basic_string ()
#2 0x041fc8c7 in sql::SQLString::SQLString (this=0xb02e6a4c,
s=0x4beccb0 "", n=0) at sqlstring.h:43
sql::SQLString temp = res->getString(colNum); // getString
basically does "return sql::SQLString(p, 0);" where p points to a
new char[23]
I don't know if it will help you track down the problem or not, but I
don't think there is any temporary SQLString being created here. If I
recall, any modern compiler will almost certainly construct the object
in place, not create a temporary. So stack-trace line #2 should be
creating the variable "temp" itself, not a temporary. This avoids the
overhead of calling an assignment operator and destroying the
temporary. But like I said, I don't know if that will help you track
down the problem.
However, the fact that your "toy" program doesn't misbehave makes me
suspect that you've got a bug elsewhere in the code that is only being
*exhibited* when this code is run. That's a common problem, and can
often be caused by using uninitialized pointer variables, by buffer
overruns, or by deleting an object twice.
-Howard
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