Re: Variable to sizeof function.

[Vikas S <vikas_soolapani@yahoo.com>]

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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> > 
> > 
> > 
> > 
> > 
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> 
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