Re: STL, memory allocation, and cleanup (gcc 3.0?)

[elf@florence.buici.com]

On Mon, Nov 19, 2001 at 03:59:29PM +1100, Brian May wrote:
> >>>>> "elf" == elf  <elf@florence.buici.com> writes:
> 
>     elf> I've written a C++ program to demonstrate behavior that I
>     elf> cannot explain.  It appears that the STL allocates memory
>     elf> that it never frees.  I'd like to believe that I'm missing
>     elf> something obvious, but then it must not be obvious enough.
>     elf> Yes, I've run the debugger on it.  It looks to be a GCC bug,
>     elf> but I cannot be sure since I don't have an explanation for
>     elf> the fact that a large block is allocated for the first Map
>     elf> and not for the second, *and* there are no static members in
>     elf> the Map template.
> 
>     elf> The program hooks new/delete and malloc/free, printing
>     elf> messages when one is called.  This all arose because I am
>     elf> using nearly identical code in another application to prove
>     elf> that it is memory conservative.
> 
> I get:
> 
> map_p
> malloc 12 -> 0x8053808
> malloc 960 -> 0x8053818
> free 0x8053808
> map_p
> malloc 12 -> 0x8053808
> free 0x8053808

Yep.  That's it.

> This looks like (to me anyway) that 960 bytes memory is getting
> allocated by STL, and it is allocated static so that it gets shared by
> subsequent calls by whatever uses it.

I haven't been able to find where this could be happening.  I've read
through the template code without finding anything that could explain
this.  

>     elf> Questions include:
> 
>     elf>   1) Is there a gcc 3.0 machine I can use to run this test?
> 
> I got compile errors. Sorry, I don't know what is wrong either :-)

Hmm.  I'm not sure why you'd be getting syntax errors.  Did you start
your source file with the comment?  It looks like it doesn't link my
typedefs.  

How about returning me a preprocessed version?

  gcc -E -c -o freetest.i freetest.cc

> [521] [scrooge:bam] ~ >gcc-3.0 -o freetest freetest.cc      
> freetest.cc:24: syntax error before `;' token
> freetest.cc:25: syntax error before `;' token
> freetest.cc:30: 'Map' is used as a type, but is not defined as a type.
> freetest.cc: In function `void test_list()':
> freetest.cc:78: `list' undeclared (first use this function)
> freetest.cc:78: (Each undeclared identifier is reported only once for each 
>    function it appears in.)
> freetest.cc:78: parse error before `*' token
> freetest.cc: In function `void test_list_p()':
> freetest.cc:83: parse error before `*' token
> freetest.cc:84: `pl' undeclared (first use this function)
> freetest.cc: In function `void test_map()':
> freetest.cc:89: `Map' undeclared (first use this function)
> freetest.cc:89: parse error before `;' token
> freetest.cc:90: `m' undeclared (first use this function)
> freetest.cc:90: `Pair' undeclared (first use this function)
> freetest.cc: In function `void test_map_p()':
> freetest.cc:95: `pm' undeclared (first use this function)
> freetest.cc:95: parse error before `;' token
> 
> suggestion: compile with -Wall. This will catch errors like:
> 
> freetest.cc: In function `void * _malloc(unsigned int)':
> freetest.cc:41: warning: unsigned int format, pointer arg (arg 3)
> freetest.cc: In function `void _free(void *)':
> freetest.cc:47: warning: unsigned int format, pointer arg (arg 2)
> 
> (sorry about messing up the formatting...)
> 
>     elf> void* _malloc (size_t cb) { void* pv = malloc (cb); printf
>     elf> ("malloc %d -> 0x%x\n", cb, pv); return pv; }
> 
>     elf> void _free (void* pv) { printf ("free 0x%x\n", pv); free
>     elf> (pv); }
> 
> pointers should be %p, not %x. This will avoid the warning. When you
> use %p, you don't need to append the 0x at the front, it will happen
> automatically.

...must...break...free...old...habit...

> -- 
> Brian May <bam@debian.org>
> 
> 
> -- 
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