Thread: global pointer problem?

You do not initialise the 'next' pointer, the other code assumes that it is set to NULL:

Code:

    // Set default values.
    new->lexeme=str;
    new->next = NULL;  // <-- add this line

... and now it works (on my machine at least and within my
understanding of what you want it to do )

im not sure but if that was the prob
would not ...

while( pTmp->next ) {
pTmp = pTmp->next;
}

cause a segmentation fault?

the NULL should be set but my compiler (gcc) seems to do it automaticly, and the original code posted runs perfectly on my computer?

you shouldn't declare variables in a header file. I don't know if that's your problem but it could cause you not to work if you use that header file in more than one module

>would not ... <snip> cause a segmentation fault?

It did under my compiler (MSVCv6). I do not have gcc here to
test what that does. K&R states that malloc() does not initialise
the memory that it allocates - calloc() does. Any other behaviour
(e.g. initialising memory to zero) is compiler specific. The fact that
this code happens to work when compiled with gcc is actually
bad marks for gcc since it encourages non-portable code. For
once (!) MSVC does the sensible thing and crashes out in a very
obvious manner.

If the question was how to print out the whole structure every
time then this should work:

Code:

ENTRY *addEntry(char *str)
{
  ENTRY *pTmp=symPtr;
  ENTRY *new;
  new=(ENTRY *)malloc(sizeof(ENTRY));
  if(!new) {
    fprintf(stderr, "Could not add a new entry to symbol table\n");
    exit(1);
  }

  // Set default values.
  new->lexeme=str;
  new->next = NULL;
  
  if(!pTmp) {
    symPtr=new;
    fprintf(stderr, "added %s\n", str);
  }
  else {
    while(pTmp->next)
      pTmp=pTmp->next;
    pTmp->next=new;
    fprintf(stderr, "%s added\n",str);
  }

  // print out entire list
  fprintf(stderr, "list now contains:\n");
  for (pTmp = symPtr; pTmp != NULL; pTmp=pTmp->next)
    fprintf(stderr, "%s\n",pTmp->lexeme);

  return new;
}

if the error being received on Lilgirls comp was not a segmentation fault then her compiler may be doing the same thing... whether it should or shouldnt be doing so.

it only prints the last node that was added

There is probably another error elsewhere in the program that is causing this fault!

Originally posted by Monster

Code:

new->lexeme=str;

I think this is your problem. You are assigning a pointer. Next time you read a name this value (lexeme) will also change because they are both pointing to the same menory area. You need to copy the value to lexeme (allocate memory and copy) to get it working. For example use strdup (don't forget to free memory when deleting the node).

Entirely possible. However, if 'str' is a string allocated elsewhare, this works fine. Also, if 'str' is a string literal, this will also work just fine.

Code:

addEntry( "This" );
addEntry( "works" );
addEntry( "just" );
addEntry( "fine" );
addEntry( "." );
addEntry( "No" );
addEntry( "allocation" );
addEntry( "needed" );
addEntry( "." );

Quzah.