Re: Variable to sizeof function.

[Eric Bambach <eric@cisu.net>]

Vika,

 Perhaps you can add a sizeof field to your structures and query it?

 struct s{
   int a;
   float b;
   int mysize = sizeof(s);
 };

 int function(struct *s){
  return s->mysize;
 }

Pardon my code, its more like psuedocode than anything that will compile, but 
the idea is there. The problem is if you have pointers to strings in your 
struct, then it won't get the size properly at run-time, but if they're all 
static elements, it may work.
 
On Saturday 16 July 2005 01:44 am, Vikas S wrote:
> Thanks, This is a workable solution.
> But the issue is I've some 100+ structures. So, writing
> a if or case is going to be difficult.
>
> a) You are right.
> b) Yes. I want to pass a structure name. ie, make sizeof
> accept a variable.
>
> Is this impossible?
>
> Thanks,
> Vikas
>
> --- Steve Graegert <graegerts@gmail.com> wrote:
> > On 7/15/05, Vikas S <vikas_soolapani@yahoo.com> wrote:
> > > I guess I was not clear. Say, we have two structures.
> > >
> > > str1 {int x, char y} and str2 {int x, char *y};
> >
> > OK...
> >
> > > printf(sizeof(struct str1)); will give proper output. ie memory
> > > occupied by str1.
> >
> > ...reasonable...
> >
> > > What I want is, instead of hard-coding str1 etc., I want to find
> > > the size of structure which I will give as 1st argument. So, if the
> > > program name is size, i'll give:
> > > $ ./size str1 --- to get size of str1
> > > $ ./size str2 --- to get size of str2
> >
> > This makes things even more confusing to me.  So, you want
> >
> >     (a)    query the size of a particular structure among others
> >     (b)    provide a structure as an argument to your program
> >
> > identified by name?  Obviously (b) is something completely impossible,
> > obscure at least.  The solution to (a) is simple:
> >
> >     struct s1 { int i; char *c; } str1;
> >     struct s2 { int i; char c[5]; } str2;
> >
> >     if (argc != 2) return 0;
> >
> >     if (!strcmp(argv[1], "str1"))
> >         printf("sizeof(str1): %d\n", sizeof(str1));
> >     else
> >         printf("sizeof(str2): %d\n", sizeof(str2))
> >
> > $ cc -o test test.c
> >
> > $ ./test str2
> > sizeof(str2): 12
> >
> > > The code which I gave earlier is giving compile-time error message.
> > >
> > > Thanks,
> > > Vikas
> > >
> > > --- Rechberger Markus <mrechberger@gmail.com> wrote:
> > > > strlen on a null pointer will segfault...
> > > > if arc is 1 then argv[0] will contain a pointer to an array of char
> > > > if arc is 2 then argv[1] (the users first argument) will contain an
> > > > array of char..
> > > > so don't forget to check the number of arguments ..
> > > >
> > > > On 7/15/05, Vadiraj <vadiraj.cs@gmail.com> wrote:
> > > > > Vikas,
> > > > >
> > > > > On 7/15/05, Vikas S <vikas_soolapani@yahoo.com> wrote:
> > > > > > I want to find out the size of a structure which the user will
> > > > > > give as an argument as follows.
> > > > > >
> > > > > > #include <>  -- All includes..
> > > > > > ..
> > > > > > main(int arc, char *argv[])
> > > > >
> > > > >    argv is a charecter pointer . You cannot pass struct * as an
> > > > > arguement to main.
> > > > >
> > > > > > {
> > > > > > printf("Size of structure %s is: %d\n", argv[1], sizeof(struct
> > > > > > argv[1]));
> > > > >
> > > > > use strlen(argv[1]) to find the lenght of the string.
> > > > >
> > > > > --
> > > > > cheers,
> > > > > Vadi
> > > > > -
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-- 
----------------------------------------
--EB

> All is fine except that I can reliably "oops" it simply by trying to read
> from /proc/apm (e.g. cat /proc/apm).
> oops output and ksymoops-2.3.4 output is attached.
> Is there anything else I can contribute?

The latitude and longtitude of the bios writers current position, and
a ballistic missile.

                --Alan Cox LKML-December 08,2000 

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