Converting string to integer...

Say I have a string (str) that contains a very long signed integer, like +1234567890 or -1234567890. How can I convert this string to an integer value that will preserve all 10 values (including the sign would be nice too)? I've tried functions like atol but it doesn't work. A small code example should suffice.

Thanks.

This seemed to work perfectly fine for me:

Code:

---

#include <iostream.h>
#include <windows.h>
#include <stdio.h>

int main()
{
        char strNumber[20] = "-3003820";
        long number;
        //strNumber[0] = '0';
        number = strtol( strNumber, '\0', 10 );

        printf("String was: %s, number is: %i", strNumber, number );

        return 0;
}

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Search the board. Not too long ago there was a thread full of information on this topic. I believe it was called 'atoi??' or something like that. Always search the board before posting a question.

Nice try, but that didn't work for numbers like +9999999999. Searching the board didn't really help. Any takers?

Here's my stab at it:

Code:

---

long bigatoi (const char* n)
{
        int neg = 0;
        if (n[0] == '-')
                neg = 1;
       
        int l = strlen(n);
        int i = neg;
        long c = pow(10,(l-1-neg));
        long num = 0;

        for (; i < l; ++i)
        {
                num += ((int)(n[i]-48) * c);
                c /= 10;
        }

        if (neg)
                return -num;

        return num;
}

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There's plenty of ways that code could be better, I'm sure.

The problem is that really big numbers are require more space. You can replace the long c =, long num = and return type with long doubles, which have more space (tried it but numbers come back in sci. notation)...

I'll try to improve this code...

I dunno how to get it to work with bigger numbers =)

Another way would be to create (or use a preexisting, perhaps) "big number" class, that can store and work with numbers with very long digit counts.

Code:

---


int
 as_int(const char c)
{
 return c - 0x30;
}


template <class number>
number
 power(number value, int exp)
{
 if(exp < 1) return 1;
 number result = value;
    while(--exp)
  {
    result *= value;
  }
 return result;
}


template <class number>
number
 aton(const char * input)
{
 int x = 0;
 number value = 0;
 char * p = (char*)&input[ strlen(input) ];
  while(p != &input[0])
 {
    --p;

      if(isdigit(*p))
    {
      value += ( as_int(*p) * power<number>(10, x++) );
    }
    else if(*p == '-')
    {
      value = -value;
    }
  }
 return value;
}





int main(){
char buff[100];

  do
  {
    cout << "...enter a number, '0' to exit..." << endl;
    cin.getline(buff, 100);
    cout << aton<long long int>(buff) << endl;
  }while(aton<long long int>(buff) != 0);

 cin.get();
return 0;
}

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