Converting 32 bit binary IP to decimal IP (vice-versa)

Hello,

I am new to this site and the program language of C.

I am trying to create a program that would allow me to convert 32 bit binary (in chunks of 8 bits) ip to decimal ip. Also, I am trying to convert from decimal ip to 32 bit binary ip.

I am totally lost to convert 32 bit binary to decimal ip but I think I have an understanding of converting decimal ip to 32 bit binary ip.

Any help would be greatly appreciated.

Here is the code I have so far for decimal IP to Binary IP (Am I missing anything?)

Code:

---

{
// Initialize the variables
unsigned long a,b,c,d,base10IP;

// Get the IP address from user
cout << "\nEnter an IP address in dotted quad notation (x.x.x.x)";
cout << "\nwith each section seperated by a space: ";
cin >> a >> b >> c >> d;

// Do calculations to covert IP to base 10
a *= 16777216;
b *= 65536;
c *= 256;
base10IP = a + b + c + d;

// Output new IP address
cout << "\nThe converted address is: " << base10IP << '\n';
}

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I was of the impression that there were already macros to handle these things. why not do it like this:

Code:

---

union ip
{
  int ip32;
  char ip8x4[4];
};

---

The union seems OK, but a more portable solution would be to (use the macros you are talking about, but in their absence...) shift values out one at a time, and then you don't have to worry about big/little endianness.

Peel each 8-bit part off:

Code:

---

#define IPCOMP(addr, n) ((addr >> (24 - 8 * n)) & 0xFF)

printf("%d.%d.%d.%d", IPCOMP(addr, 0), IPCOMP(addr, 1), IPCOMP(addr, 2), IPCOMP(addr, 3));

---

Which is why using the constructs from socket programming are wisest, in my humble opinion.

Quote:

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Originally Posted by brewbuck

Peel each 8-bit part off:

Code:

---

#define IPCOMP(addr, n) ((addr >> (24 - 8 * n)) & 0xFF)
 
printf("%d.%d.%d.%d", IPCOMP(addr, 0), IPCOMP(addr, 1), IPCOMP(addr, 2), IPCOMP(addr, 3));

---

---

Wrong direction, homie.

Wow, quick replies. Thank you!

Here is the other code I am trying to incorporate.

Maybe I am doing things wrong since I am a newb - I am trying to break things down one at a time instead of doing the project as a whole. I have a feeling that I am not doing everything correctly. Thanks again for the assistance.

Code:

---

#include <stdio.h>
#include <stdlib.h>
main()
{
int choice;

do
{ printf("Select from one of the choices:\n");
  printf("1.) Convert from 32 bit binary ip form to dotted decimal ip form\n");
  printf("2.) Convert from dotted decimal ip form to 32 bit binary ip form\n");
  printf("3.) Convert a dotted decimal ip form to it's class and display the network portions separately\n");
  printf("4.) Convert from CIDR slash notation to dotted decimal ip form\n");
  printf("5.) Convert from subnet dotted ip form to CIDR slash form\n");
  printf("6.) Quit the the program\n");
printf("Enter your choice: ");
scanf(" %d", &choice);
switch (choice)
  {
case (1) : printf("1.) Convert from 32 bit binary ip form to dotted decimal ip form\n");
break;
case (2) : printf("2.) Convert from dotted decimal ip form to 32 bit binary ip form\n");
// Initialize the variables
unsigned long a,b,c,d,base10IP;

// Get the IP address from user
cout << "\nEnter an IP address in dotted quad notation (x.x.x.x)";
cout << "\nwith each section seperated by a space: ";
cin >> a >> b >> c >> d;

// Do calculations to covert IP to base 10
a *= 16777216;
b *= 65536;
c *= 256;
base10IP = a + b + c + d;

// Output new IP address
cout << "\nThe converted address is: " << base10IP << '\n';
break;
case (3) : printf("3.) Convert a dotted decimal ip form to it's class and display the network portions separately\n");
break;
case (4) : printf("4.) Convert from CIDR slash notation to dotted decimal ip form\n");
break;
case (5) : printf("5.) Convert from subnet dotted ip form to CIDR slash form\n");
break;
case (6) : exit(0);
break;
default  : printf("I don't know the ");
          printf("option %d. \n", choice);
          printf("Try again. \n");
          break;
  }
system("clear");
} while(1);
}

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Quote:

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Originally Posted by master5001

Wrong direction, homie.

---

Why is that?

Oh wait... when I said that to you, I meant to quietly mutter it to myself instead.

well my code from decimal to binary didn't work because cout and cin are not found in C but found in C++. Does anybody have any suggestions because I am getting really frustrated??

I know there were suggestions but there seems to be conflicts back and forth. What should I use?

In C you would use scanf instead of cin, and printf instead of cout.

--
Mats

Well I finally got the code working but I didn't get it to convert to binary :(

How can I express this operation of decimal to binary like this.
ex:
IP - 172.16.10.15
If I did each number at a time, like if I started with 172.
Ton convert 172 to Binary, I would have to:
1. First divide the number by 2. The remainder will be either 0 or 1.
2. Write down the remainder.
3. Divide the remaining number without the remainder by 2. Again, the remainder will be either 1 or 0.
4. Write down the remainder to the left of the previous remainder.
5. Repeat this until you end up with 0.

For 172, the formula would look like this:

172 / 2 = 86 remainder 0
86 / 2 = 43 remainder 0
43 / 2 = 21 remainder 1
21 / 2 = 10 remainder 1
10 / 2 = 5 remainder 0
5 / 2 = 2 remainder 1
2 / 2 = 1 remainder 0
1 / 2 = 0 remainder 1

So the binary number for 172 = 10101100

For 15:
If I used a smaller number such as 15, I would have reached 0 before I had 8 bits. If this occurs, I have to fill in the remaining bits with 0s. For example:

15 / 2 = 7 remainder 1
7 / 2 = 3 remainder 1
3 / 2 = 1 remainder 1
1 / 2 = 0 remainder 1

Because I got to 0 in only four steps, the remaining bits are 0--so the binary of 15 is 00001111.

How can I express this in code

If anybody cares here is the working code - it converts dotted IP to decimal.

Code:

---

case (2) : printf("2.) Convert from dotted decimal ip form to 32 bit binary ip form\n");
{
          // Initialize the variables
            unsigned long a,b,c,d,e;
          // Get IP Address from user
          printf("Enter a dotted decimal IP address in dotted quad notation (x.x.x.x)\n");
          printf("with each section seperated by a space: \n");
          scanf(" %a.%b.%c.%d", &firstip, &secondip, &thirdip, &fourthip);
          // Do calculations to convert IP to base 10
          a *= 16777216;
          b *= 65536;
          c *= 256;
          e  = a + b + c + d;
          // The 32 bit binary IP form
          scanf(" %e", &answer);
          // Listing Answer
          printf("\nThe bit binary IP you wanted is listed below.\n");
          printf("Request: %e");
          return 0;
}
break;

---

Post the code you have thus far for the IP-to-decimal conversion.

If anybody wants to know the end code - here it is
Thanks for the help everyone!

Code:

---

//************************************************************************
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// read an IP address in binary form
// store it into an array of 4 strings of 8 chars each
// return 1 if read successfully or 0 if an error occurred
  int readBinary(char bin[4][8]) {
  char binString[80];
  int i, j;
  int nextChar = 0;
  int len;

// read line
  printf("Enter 32-bit IP address in binary form (xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx): ");
  fflush(stdout); //flushes the output, it is needed on some version of linux/unix before scanf
  scanf("%[^\r\n]", binString);

// store binary digits into bin array
  len = strlen(binString);
  for (i=0; i<4; i++) {
    if (nextChar >= len) {
      printf("Invalid input string (too short)\n");
      return 0;
    }
    for (j=0; j<8; j++) {
// skip spaces
      while (nextChar < len && binString[nextChar] == ' ')
        nextChar++;
// end of string? break the loop
      if (nextChar >= len) {
        printf("Invalid input string (too short)\n");
        return 0;
      }
      bin[i][j] = binString[nextChar];
      nextChar++;
// only 0 and 1 accepted
      if (bin[i][j] != '0' && bin[i][j] != '1') {
        printf("Invalid input string (not a binary number)\n");
        return 0;
      }
    }
  }

// return 1 (OK)
  return 1;
}

// read an IP address in decimal dotted form
// return 1 if ok or 0 if an error occurs
  int readIPAddress(int ipaddr[]) {
  char decstring[4][4];
  int i;

// read IP address as strings
  printf("Enter 32-bit IP address in dotted decimal notation (xxx.xxx.xxx.xxx): ");
  fflush(stdout);
  if (scanf("%[^.].%[^.].%[^.].%[^\r\n]", decstring[0], decstring[1], decstring[2], decstring[3]) < 4) {
    printf("Invalid input string (wrong IP address format)\n");
    return 0;
  }

// convert each string to integer
  for (i=0; i<4; i++) {
    ipaddr[i] = atoi(decstring[i]);  // atoi converts a string to an integer
    if (ipaddr[i] < 0 || ipaddr[i] > 255) {
      printf("Invalid input string (incorrect numbers for IP address)\n");
      return 0;
    }
  }

  return 1;
}

// read an IP address slash netmask length (CIDR format)
// return 1 if ok or 0 if an error occurs
int readIPSlashAddress(int ipaddr[], int *slash) {
  char decstring[4][4];
  char slashstring[3];
  int i;

// read IP address as strings
  printf("Enter IP-address in CIDR notation (xxx.xxx.xxx.xxx/xx): ");
  fflush(stdout);
  if (scanf("%[^.].%[^.].%[^.].%[^/]/%[^\r\n]", decstring[0], decstring[1], decstring[2], decstring[3], slashstring) < 5) {
    printf("Invalid input string (wrong IP address format)\n");
    return 0;
  }

// convert each string to integer
  for (i=0; i<4; i++) {
    ipaddr[i] = atoi(decstring[i]);
    if (ipaddr[i] < 0 || ipaddr[i] > 255) {
      printf("Invalid input string (incorrect numbers for IP address)\n");
      return 0;
    }
  }

  *slash = atoi(slashstring);  // a variable and it stores the netmask-length
  if (*slash < 0 || *slash > 32) {
    printf("Invalid input string (invalid netmask length)\n");
    return 0;
  }

  return 1;
}

// read an IP address slash netmask
// return 1 if ok or 0 if an error occurs
  int readIPMaskAddress(int ipaddr[], int mask[]) {
  char decstring[4][4];
  char maskstring[4][4];
  int i;

// read IP address as strings
  printf("Enter IP-address/subnet you want converted to CIDR slash form (xxx.xxx.xxx.xxx/xxx.xxx.xxx.xxx.): ");
  fflush(stdout);
  if (scanf("%[^.].%[^.].%[^.].%[^/]/%[^.].%[^.].%[^.].%[^\r\n]", decstring[0], decstring[1], decstring[2], decstring[3],
      maskstring[0], maskstring[1], maskstring[2], maskstring[3]) < 8) {
    printf("Invalid input string (wrong IP address/netmask format)\n");
    return 0;
  }

// convert each string to integer
  for (i=0; i<4; i++) {
    ipaddr[i] = atoi(decstring[i]);
    if (ipaddr[i] < 0 || ipaddr[i] > 255) {
      printf("Invalid input string (incorrect numbers for IP address)\n");
      return 0;
    }
  }

// convert each string to integer
  for (i=0; i<4; i++) {
    mask[i] = atoi(maskstring[i]);
    if (mask[i] < 0 || mask[i] > 255) {
      printf("Invalid input string (incorrect numbers for netmask)\n");
      return 0;
    }
  }
  return 1;
}

void convertBinToDec(char bin[4][8], int dec[]) {

  int i, j;

// convert each binary group to decimal number
  for (i=0; i<4; i++) {
    dec[i] = 0;
    for (j=0; j<8; j++) {
      dec[i] *= 2;
      if (bin[i][j] == '1')
        dec[i]++;
    }
  }

}

void convertDecToBin(int dec[], char bin[4][9]) {

  int i, j;

// convert each decimal group to binary
  for (i=0; i<4; i++) {
    for (j=7; j>=0; j--) {
      bin[i][j] = (dec[i] & 1) + '0';
      dec[i] /= 2;
    }
    bin[i][8] = 0;
  }

}

// show network and host parts
void showNetworkHost(int ipaddr[], int numNetwork) {
  int i;

  printf("Network portion is: ");
  for (i=0; i<=numNetwork; i++)
    printf("%d.", ipaddr[i]);
  printf("\n");

  printf("Host portion is: ");
  for (i=numNetwork+1; i<4; i++)
    printf(".%d", ipaddr[i]);
  printf("\n");
}

void convertCIDRToNetmask(int slash, int mask[]) {

// create binary mask first, then convert to decimal
  char bin[4][8];
  int i, j;

// write 1's while slash is positive, then write 0's
  for (i=0; i<4; i++)
    for (j=0; j<8; j++) {
      if (slash > 0) {
        bin[i][j] = '1';
        slash--;
      }
      else
        bin[i][j] = '0';
    }

// convert to decimal
  convertBinToDec(bin, mask);
}

  int convertNetmaskToCIDR(int mask[], int *slash) {
// create binary mask first, then convert to slash form
  char bin[4][9];
  int i, j;
  char lastChar;

  convertDecToBin(mask, bin);

// add to slash while 1's are found
  lastChar = '1';
  *slash = 0;
  for (i=0; i<4; i++)
    for (j=0; j<8; j++) {
      if (bin[i][j] == '1') {
// once a zero is found - no more 1's should appear
        if (lastChar == '0') {
          printf("Cannot convert netmask to CIDR notation\n");
          return 0;
        }
        (*slash)++;
      }
      lastChar = bin[i][j];
    }

  return 1;
}

int main()
{
  int choice;
  char bin[4][8];
  char bin2[4][9];
  int ipaddr[4];
  int mask[4];
  int slash;

// temp string, used when reading - used to skip any remaining input after reading
// a menu option in the main menu.  The main menu scanf reads an integer.  If a temp
// string wasn't used, the next scanf trying to read a string would read an empty string
  char temp[80];

  do
  {
    printf("\nSelect from one of the choices:\n\n");
    printf("1) Convert from 32 bit binary ip form to dotted decimal ip form\n");
    printf("2) Convert from dotted decimal ip form to 32 bit binary ip form\n");
    printf("3) Convert a dotted decimal ip form to its class and display the network and host portions separately\n");
    printf("4) Convert from IP/CIDR slash notation to dotted decimal ip form\n");
    printf("5) Convert from IP/subnet dotted ip form to CIDR slash form\n");
    printf("6) Quit the program\n");
    printf("\nEnter your choice: ");
    fflush(stdout);
    scanf("%d", &choice);
    scanf("%[^\n]", temp);
    scanf("%c", temp);

    switch (choice)
    {
      case (1) : // Convert from 32 bit binary ip form to dotted decimal ip form

                if (!readBinary(bin))
                  break;

                convertBinToDec(bin, ipaddr);

                // print the resulting IP
                printf("The address converted to decimal is: %d.%d.%d.%d\n", ipaddr[0], ipaddr[1], ipaddr[2], ipaddr[3]);

                break;

      case (2) : // Convert from dotted decimal ip form to 32 bit binary ip form
                if (!readIPAddress(ipaddr))
                  break;

                convertDecToBin(ipaddr, bin2);

                // print the results
                printf("The address converted to binary is: %8s %8s %8s %8s\n", bin2[0], bin2[1], bin2[2], bin2[3]);
                break;

      case (3) : // Convert a dotted decimal ip form to its class
                if (!readIPAddress(ipaddr))
                  break;

                if (ipaddr[0] < 128) {
                  printf("This address belongs to class A\n");
                  showNetworkHost(ipaddr, 0);
                }
                else if (ipaddr[0] < 192) {
                  printf("This address belongs to class B\n");
                  showNetworkHost(ipaddr, 1);
                }
                else if (ipaddr[0] < 224) {
                  printf("This address belongs to class C\n");
                  showNetworkHost(ipaddr, 2);
                }
                else if (ipaddr[0] < 240)
                  printf("This address belongs to class D\n");
                else
                  printf("This address belongs to class E\n");

                break;
      case (4) : // Convert from IP CIDR slash notation of to dotted decimal ip form
                if (!readIPSlashAddress(ipaddr, &slash))
                  break;

                convertCIDRToNetmask(slash, mask);

                printf("IP/Netmask in dotted decimal IP form: %d.%d.%d.%d/%d.%d.%d.%d\n",
                    ipaddr[0], ipaddr[1], ipaddr[2], ipaddr[3], mask[0], mask[1], mask[2], mask[3]);

                break;

      case (5) : // Convert from IP/subnet form to CIDR slash form
                if (!readIPMaskAddress(ipaddr, mask))
                  break;

                if (!convertNetmaskToCIDR(mask, &slash))
                  break;

                printf("IP/Netmask-length in CIDR notation: %d.%d.%d.%d/%d",
                    ipaddr[0], ipaddr[1], ipaddr[2], ipaddr[3], slash);

                break;

      case (6) : system("clear"); //clear program
                exit(0); // close program

      default  : printf("I don't know the option %d.\n", choice);
                printf("Try again.\n");
                break;
    }
  } while(1);
}

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I would highly recommend using the existing libraries that are used for this sort of thing. Please check out the use of

#include <arpa/inet.h>


http://www.opengroup.org/onlinepubs/...inet_addr.html