Re: Do you use a garbage collector (java vs c++ difference in "new")

From:

Silvio Bierman <sbierman@jambo-software.com>

Newsgroups:

comp.lang.c++,comp.lang.java.programmer

Date:

Sat, 12 Apr 2008 14:21:01 +0200

Message-ID:

<4800a934$0$14348$e4fe514c@news.xs4all.nl>

Razii wrote:

On Thu, 10 Apr 2008 20:37:59 -0500, Razii
<DONTwhatevere3e@hotmail.com> wrote:

int main(int argc, char *argv[]) {

    clock_t start=clock();
      for (int i=0; i<=10000000; i++) {
    Test *test = new Test(i);
    if (i % 5000000 == 0)
        cout << test;
  }

If I add delete test; to this loop it gets faster. huh? what the
exaplanation for this?

2156 ms

and after I add delete test; to the loop

1781 ms

why is that?

Because new in C++ does NOT directly call an OS allocation function. C++
internally uses something similar to malloc/free from C which are memory
management functions that use OS allocation functions as its base but
keeps a self-maintained heap of, allocated at the OS level but
unallocated at the application level, free blocks.

If you keep allocating with new without using delete the OS allocations
have to be done. If you use delete the block goes into the free-blocks
heap and is probably returned immediately with the next new call. You
probably see the same memory address each time through the loop.

Regards,

Silvio Bierman