help needed on stl string ( reserve vs resize )

["Jyotirmoy Das" <Jyotirmoy_Das at infosys dot com>]

Hi All,
  I have the following sample code (try.cpp) which crashes on Linux AS
2.1. I am using gcc 2.96. Problem is that after using reserve, capacity
remains same. As a result, I am not able to the string. 
  If I use resize in place of reserve, it works fine. Can someone
explain this behavior? Moreover, I do not want to use resize, as it will
change the length of string.

TIA, 
Jyoti

==================================================================
[jdas@linux2 cpp]$ cat try.cpp

#include <string>
using namespace std;

int main()
{
  string * m;
   m = new string();
  cout << "length=" << m->length() << "  capacity=" << m->capacity() <<
endl;
  //m->resize(10); 
  m->reserve(10);  // In my program, this does not make an impact on 
			// capacity 
  cout << "length=" << m->length() << "  capacity=" << m->capacity() <<
endl;
  char * str = const_cast<char *> (m->c_str());
  *str++ = 'a'; // since my capacity is still the zero, so it dumps core
  *str++ = 'b';
  *str++ = 'c';
  *str = '\0';
  cout << "string=" << m->c_str();
  return 0;
}
======================================================================
[jdas@linux2 cpp]$ /usr/bin/g++ -v
Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/2.96/specs
gcc version 2.96 20000731 (Red Hat Linux 7.2 2.96-108.1)

[jdas@linux2 cpp]$ g++ -g try.cpp 

[jdas@linux2 cpp]$ ./a.out 
lenght=0  capacity=0
lenght=0  capacity=0
Segmentation fault (core dumped)