Problem with arrays and pointers

Im stuck with a problem I need to do for one of my classes...After doing a count I have to declare a char pointer array of the token count size dynamically. In the function findTokens() I have to search through the string, put the address of each token into the pointer array, and change the colon separator to the null character. This is what I got but it doesn't want to work...Any help out there?

Code:

---

//...
int main(void)
{
 //local declerations
 char theString[] = "abcd0001:groupno:userno:name:/bin/ksh";
 char colon=':';
 int count;
 count = countToken(theString,colon);
  cout << " Number of tokens in string are: " << count;
 char **ptr;
 ptr = new char*[count];
 blah = findTokens(theString, ptr,colon);
 for (int j=0; j < 6; j++)
 {
 cout << " Token "<<j<<": " <<blah <<endl<<endl;
 }
}//main

int countToken(char theString[], char colon)
{
  int count = 1;  // Initialise at one
  int len = strlen(theString);
  for(int n = 0; n < len; n++)  // Loop from character zero to end of string
  {
    if (theString[n] == colon) // Check characters one by one
    {
      count++;
    }
  }
  return count;
}
char findTokens(char* theString, char **ptr, char colon)
{
 int index=0;
 **ptr[index] = *theString;
 index++;
  while(*theString)
  {
      if(*theString == colon)
      {
      **ptr[index] = (*theString + 1);
      *theString = '\0';
      }

  *theString++;
  }
  return;
}

---

Your indirection was off and a few things needed to be shuffled. The changes needed were minor:

Code:

---

#include <iostream>

using namespace std;

int countToken(char theString[], char colon)
{
  int count = 1;  // Initialise at one
  int len = strlen(theString);
  for(int n = 0; n < len; n++)  // Loop from character zero to end of string
  {
    if (theString[n] == colon) // Check characters one by one
    {
      count++;
    }
  }
  return count;
}
void findTokens(char* theString, char **ptr, char colon)
{
  int index=0;

  ptr[index++] = theString;

  while(*theString)
  {
    if(*theString == colon)
    {
      *theString = '\0';
      ptr[index++] = (theString + 1);
    }
   
    theString++;
  }
  return;
}

int main(void)
{
  //local declarations
  char theString[] = "abcd0001:groupno:userno:name:/bin/ksh";
  char colon=':';
  int count;
 
  count = countToken(theString,colon);
  cout << "Number of tokens in string are: " << count <<endl;
 
  char **ptr;
  ptr = new char*[count];
 
  findTokens(theString, ptr,colon);
 
  for (int j=0; j < count; j++)
  {
    cout << " Token "<<j<<": " <<ptr[j] <<endl<<endl;
  }
}//main

---

-Prelude

Thanks so much Prelude!!!!

I don't have my compiler to try the following function, but I think there are some problems in it anyway. See comments.

Code:

---

void findTokens(char* theString, char **ptr, char colon)
{
  int index=0;

  ptr[index++] = theString;

  //you can't assign one Cstyle string to another, use strcpy() instead
  //each ptr[index] needs to have memory declared.  You need another loop with call to new operator to do this, probably back in main()
  //you don't want to assign the entire length of theString to ptr[0] either, you want just the firtst token from theString in ptr[0]
 

  while(*theString)//this looks for the null char at end of theString
  {

    if(*theString == colon)//this looks for a colon in the theString
    {

      *theString = '\0';//this replaces the colon with a null char

      ptr[index++] = (theString + 1);
      //this assigns theString, minus the current token to the next string in ptr, but it doesn't leave just the first token in ptr[index]; it leaves whatever theString was when theString was passed to ptr[index] in ptr[index] so:
    ptr[0] will be "abcd0001:groupno:userno:name:/bin/ksh"
    ptr[1] will be "groupno:userno:name:/bin/ksh"
    ptr[2] will be "userno:name:/bin/ksh"
    etc.

    }//end if
   
    theString++;
  }//end while
  return;

---

I hope that I have my thinking cap on correctly this AM, but sometimes it comes off when I am not looking, so use a compiler to try out the function---don't take me at my word.

If I am correct here's my algorithm for finding tokens and storing one token per string in ptr.

I would declare a tempString and use a different counter variable to keep track of where I am in tempString.

I would read each char into tempString from theString until I found a colon.

I would place a nul char in tempString instead of a colon

I would then assign tempString to ptr[index++]

I would then reset the counter variable for tempString to 0.

I would then move on to the next char in theString.

>//you can't assign one Cstyle string to another, use strcpy() instead
You're thinking about arrays, this is simple pointer addressing. The assignment is perfectly legal.

>//each ptr[index] needs to have memory declared.
It already is declared, the list of pointers point to different parts of theString.

>ptr[0] will be "abcd0001:groupno:userno:name:/bin/ksh"
>ptr[1] will be "groupno:userno:name:/bin/ksh"
>ptr[2] will be "userno:name:/bin/ksh"
No, remember that the colon is replaced with a nul character.

ptr[0] will be "abcd0001"
ptr[1] will be "groupno"
ptr[2] will be "userno"
etc...

This is a simple and common technique, a list of pointers reference locations in a single block of memory so that it isn't lost. When the function starts the string looks like this:

"abcd0001:groupno:userno:name:/bin/ksh"

After the function runs, theString and ptr will look like this:

Code:

---

      "abcd0001\0groupno\0userno\0name\0/bin/ksh"
        ^        ^        ^      ^    ^
        |        |        |      |    |
ptr[0]---        |        |      |    |
ptr[1]-------------        |      |    |
ptr[2]----------------------      |    |
ptr[3]------------------------------    |
ptr[4]------------------------------------

---

-Prelude

Prelude: fascinating. Your explanation was wonderful. I'll copy and run the program later.

Dupek and Prelude: Thanks for the opportunity to improve my understanding. It's why I keep coming back.