Re: Variable to sizeof function.

[Steve Graegert <graegerts@gmail.com>]

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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