data type to hold pointers?

SciYro · 05-14-2004, 11:15 PM

this is probably a stupid questions but what data type is used for pointers?

what i want to do is set up a structure that (at one of its members) will hold various pointers to other structures, which will also hold pointers to lines of text, taken from getline() (using dynamic allocation for the memory thing)

also does anyone know what size is for dynamic allocation?, getline wants me to input the size of the buffer, but since its supposed to change itself I'm not sure if there is a size..?, or should i just use sizeof() to get the size it asks for?

- thx

itsme86 · 05-14-2004, 11:21 PM

You can use void * to hold a typeless pointer. For example:

Code:

struct s1 { int a; };
struct s2 { char a; };
struct s3 { void *sptr; };

int main(void)
{
  struct s1 str1;
  struct s2 str2;
  struct s3 str3, str4;

  str3.sptr = &str1;
  str4.sptr = &str2;
}

I assume that's kind of what you're talking about anyway...

As for size during dynamic allocation. You tell malloc() how much memory to allocate so you should already know the size. You don't want to use sizeof() on a pointer to allocated memory because you'll only get the size of the pointer (e.g. 'char *ptr = malloc(10); printf("%d\n", sizeof(ptr));' will show 4, not 10 like you might expect). But if you have something like 'char buf[10]; printf("%d\n", sizeof(buf));' then it will show 10.

SciYro · 05-14-2004, 11:32 PM

right, umm, i don't know the full size of the line, but it cant be bigger then a unsigned int , so i guess ill just tell it to do that .. but also the size of the line will change when its laoded..

hmm, does anyone think it will be better to let getline() make its own buffer, then copy its contents into a dynamic buffer?

and thx for the help with the structures, i think it should work with arrays since thats what i think ill be using to keep track of the other structures as they should be changing a lot

thx again

aluser · 05-15-2004, 10:53 AM

the normal way to use getline() is like

Code:

size_t bufsiz = 0;
ssize_t linelen;
char* line = NULL;
while ((linelen = getline(&line, &bufsiz, infile)) != -1) {
        printf("Got a line length %d.  Here is the line:\n%s", linelen, line);
}
free(line);

There's an example in the man page too.

The_Nerd · 05-15-2004, 11:53 AM

Well, personally, I think you should brush up a little on your C.

SciYro · 05-15-2004, 05:24 PM

yep, looks like copying seems to be the best way for what i need

thx all