Re: Allocating vector of strings seem to crash. Allocating array of strings seems to be ok .

From:

Salt_Peter <pj_hern@yahoo.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 20 Dec 2007 09:44:01 -0800 (PST)

Message-ID:

<1c32b9c0-9c6a-4371-a723-8c49a8157e83@p69g2000hsa.googlegroups.com>

On Dec 20, 11:10 am, Rakesh Kumar <rakesh.use...@gmail.com> wrote:

Hi All -
   In a project of mine - I was trying to scale down the actual issue
to the following piece of code. I need to allocate an array of strings
and reserve the individual string to a particular size (4K) .
   I wrote 2 functions - allocVectorOfStrings() and
allocArrayOfStrings().
Each of them seem to allocate similar amounts of memory - but the
version of vectorOfStrings seem to crash with the following error -
"double free or corruption (out): 0x08055ff8 ***" .

   I was just curious if I am doing anything fundamentally wrong here
to cause the issue.

#include <iostream>
#include <cstdlib>
#include <vector>

void allocVectorOfStrings();
void allocArrayOfStrings();

void allocVectorOfStrings() {
        std::vector<std::string> * vt = new std::vector<std::string>();
        vt->reserve(50);
        for (size_t i = 0; i < vt->capacity(); ++i) {
                std::cout << "We are probably ok" << i << "\n";
                vt->operator[](i).reserve(40);

Try not to use new / delete unless you are required to do so.
You are attempting to access an element that doesn't yet exist.
reserve constructs nothing.
use vector's member function at(...) when in doubt. see below.

        }
        delete vt;

}

void allocArrayOfStrings() {
        std::string * vt = new std::string[4096];
        for (size_t i = 0; i < 1024; ++i) {
                std::cout << "We are probably ok" << i << "\n";
                vt[i].reserve(4096);
        }
        delete [] vt;

}

int main()
{
        allocArrayOfStrings();
        allocVectorOfStrings(); //This function crashes
         return EXIT_SUCCESS;

}

#include <iostream>
#include <string>
#include <vector>
#include <stdexcept>

void allocVectorOfStrings()
{
  std::vector<std::string> vt(10, "default string");
  std::cout << "vt's size is " << vt.size() << std::endl;
  for(size_t i = 0; i < vt.size(); ++i)
  {
    std::cout << "vt[ " << i << " ] ";
    std::cout << vt.at(i) << std::endl;
  }
  // uncomment for a test
  // vt.at(10) = "out or range";
}

int main()
{
  try
  {
    allocVectorOfStrings();
  }
  catch( const std::exception& e)
  {
    std::cout << "Error:";
    std::cout << e.what() << std::endl;
  }
}

/*
vt's size is 10
vt[ 0 ] default string
....
vt[ 9 ] default string
*/