Looking for some way to get correct value with long precision

Hi All
The problem is related to strtod()/atof()'s well known behaviour.
strtod()/atof() add some extra digits at the end of precision while
converting from string to double. Becasue floating-point variables
cannot represent all numbers precisely, I'm looking some way around to
solve it explicitly in the code itself so that I could get the value
property = 999999999998.90000000 for precison=8 instead of
property=999999999998.90002441

Size of float and double both is 8 bytes in my machine. and I'm using
xlC compiler on AIX plateform.

Any clue will help me immensely. Thanks.

#include <iostream.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include<wchar.h>
#include<math.h>
#include<float.h>

int main(int argc, char* argv[])
{
    char property[1024];
    int precison=0;
    memset(property, '\0', sizeof(property));
    strcpy(property, argv[1]);
    precison = atoi(argv[2]);
    cout <<"property: \"" << property << "\"" << endl;
    //sscanf ( property, "%Lf", &dl);
    //sprintf(PrpValue1, "%.*lf", precison,property);

    double doubleVal=0.0;

    if (strstr(property,"E+") != NULL || strstr(property,"E-") != NULL)
   {
     doubleVal = ( long double)strtod(property, (char **)NULL);
        //doubleVal = atof(property);
        printf("doubleVal:%.*lf\n",precison,doubleVal);
        sprintf(property, "%.*lf", precison,doubleVal);
     cout <<"E+/- :property: " << property << endl;
  }

    cout <<"final property: " << property << endl;
    free(property);
    return 0;
}

Here's the o/p.
/a.out 9.999999999989E+11 8

property: "9.999999999989E+11"
doubleVal:999999999998.90002441
E+/- :property: 999999999998.90002441
final property: 999999999998.90002441