struct question

**Dave_Sinkula** · 04-13-2008

Originally Posted by Elysia

Need pointer lessons? Here you go:
http://cpwiki.sourceforge.net/A_pointer_on_pointers
It might enlighten you a little. Pointers are just variables that contains a virtual address, nothing more, nothing less. It does not allocate memory.

Try to avoid misinforming when attempting to inform; it will serve a greater purpose.

**tabstop** · 04-13-2008

Originally Posted by -EquinoX-

well I already declare line:

char* line = NULL;

the thing is that when I remove the HashTableInsert, it kind of works

And do you think the NULL pointer points at a character array?
And for that matter, you're using &line, which means that the string is being put into the memory address of line (not where line points!), but you've only got room for maybe three letters there, not to mention you won't ever get them back out, since how do you plan to reinterpret line as a char instead of a char*?

**dwks** · 04-13-2008

You can't store any information in an ordinary char* pointer that isn't pointing at allocated memory. You should either use an array, or dynamically allocate some memory for the pointer to point to.

I haven't read the rest of this thread, but since you have free(), I'm guessing you want to use the dynamic memory approach. Try something like this

Code:

char *line = malloc(256);

[edit] It seems a few posts appeared while I was typing this one up. [/edit]

**Elysia** · 04-14-2008

You're doing wrong again. Twice, in fact.

Code:

      char* line = NULL;
      size_t line_length;
      int chars_read = getline(&line, &line_length, fr);

Did you read the link I gave you? It should give insight as to why this fails.
If you DID read it and didn't understand something, then ask.

**-EquinoX-** · 04-14-2008

doesn't actually get line fills the line for us?

**tabstop** · 04-14-2008

Originally Posted by -EquinoX-

doesn't actually get line fills the line for us?

Yes, but you have to have somewhere to put it. It will not allocate memory for you.

**matsp** · 04-14-2008

Yes, getline() should fill in the pointer for you.

--
Mats

**matsp** · 04-14-2008

Originally Posted by tabstop

Yes, but you have to have somewhere to put it. It will not allocate memory for you.

If we assume the example here is a working one, then it will:
http://linux.die.net/man/3/getline

--
Mats

**-EquinoX-** · 04-14-2008

yeah..matsp.. thanks for pointing that out.. that's the getline what I mean

**tabstop** · 04-14-2008

Originally Posted by matsp

If we assume the example here is a working one, then it will:
http://linux.die.net/man/3/getline

--
Mats

Hey what do you know. How many versions of getline does that make, three I think? The C++ one doesn't work that way, does it? (All my docs say it needs room at the pointer, but who knows.)

**-EquinoX-** · 04-14-2008

sorry guys, I should have mentioned it to you before... so why do I keep get a seg fault even though that's right?

**tabstop** · 04-14-2008

So we'll keep reading:

Code:

if (line[0] != '\t'){
	  if (rule.target != NULL){
	    rule.dependency = dep;
	    rule.buildcmd = bld;
	    rule.depSize = depIndex + 1;
	    rule.bldSize = bldIndex + 1;
	    HashTableInsert(t, rule.target, &rule);
	    RuleDestruct(&rule);
	  }
	  char* pch = strtok(line, ":");
      	  int h;
         for (h = 0; pch != NULL; h++){
	    if (h == 0){
	     rule.target = pch;
             printf("Target &#37;s\n", pch); 
	     bldIndex = 0;
	     depIndex = 0;
	    }

1. When we get here, I don't see how rule.target is set.
2. In your for-loop, I don't see how pch is going to change. (You don't change it inside the loop.) Edit: I lost a brace -- so found where pch changes; never mind.

**-EquinoX-** · 04-14-2008

okay rule.target is set? what do you mean? how can I set that?

and it seems that I am missing a free(line) here, but don't know where to put..

my point here is actually just to create a temporary rule which I can put into the HashTable.. do I have to do a malloc first? if yes then how much space do I have to malloc?

**tabstop** · 04-14-2008

Originally Posted by -EquinoX-

okay rule.target is set? what do you mean? how can I set that?

Well, I don't know. Reading the code, this is the first time I ever saw rule.target, and right away we're comparing it to something. Who knows what value is stored in there? I'm not sure what's going on here -- it appears that you're deleting the old rule maybe; but there's no guarantee that rule.target is NULL the first time you get to this point. So it's quite possible you're following garbage pointers here.