Re: Query in C

Re: Query in C

[r_zaca]

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  Hello Avinash, 

  This is a function that returns a "int value" and allows you to pass as 
parameters two data types, an "int pointer" and a "foo data". 
  Well, I think it would be helpful. 
  That's it. 


>Hello Everyone , 
> 
>   Can anyone of you please tell me.. 
> 
>       what does extern "C" int func(int *,foo) accomplish ? 
> 
>   waiting for your reply. 
> 
>regards, 
>Avinash 

Re: Variable to sizeof function.

[Steve Graegert]

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
> > > -
> > > To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
> > > the body of a message to majordomo@vger.kernel.org
> > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > >
> > -
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> >
> 
> 
> 
> 
> 
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-- 
                                 ______________________________________
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Re: Variable to sizeof function.

[Vikas S]

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
> > > > -
> > > > To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
> > > > the body of a message to majordomo@vger.kernel.org
> > > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > > >
> > > -
> > > To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
> > > the body of a message to majordomo@vger.kernel.org
> > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > >
> > 
> > 
> > 
> > 
> > 
> > __________________________________
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> 
> 
> -- 
>                                  ______________________________________
> Steve Graegert                  //
> Software Consultancy           //    Whether you know it or not, if you
> Mobile: +49 (176)  21248869   // are a hacker, you are a revolutionary.   
> Office: +49 (9131) 7126409   //  Don't worry, you're on the right side.
> ____________________________//         -- Dr Crash / Phrack 6 / phile 3
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Re: Variable to sizeof function.

[Vadiraj]

On 7/16/05, Vikas S <vikas_soolapani@yahoo.com> 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.

 Another way I can suggest would be passing the file name at command prompt.
./size foo.txt

 foo.txt should contain 100+ structure names.

read the file contents and follow steve's suggestion.


  




> 
> 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
> > > > > -
> > > > > To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
> > > > > the body of a message to majordomo@vger.kernel.org
> > > > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > > > >
> > > > -
> > > > To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
> > > > the body of a message to majordomo@vger.kernel.org
> > > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > > >
> > >
> > >
> > >
> > >
> > >
> > > __________________________________
> > > Do you Yahoo!?
> > > Yahoo! Mail - You care about security. So do we.
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> > >
> >
> >
> > --
> >                                  ______________________________________
> > Steve Graegert                  //
> > Software Consultancy           //    Whether you know it or not, if you
> > Mobile: +49 (176)  21248869   // are a hacker, you are a revolutionary.
> > Office: +49 (9131) 7126409   //  Don't worry, you're on the right side.
> > ____________________________//         -- Dr Crash / Phrack 6 / phile 3
> > -
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> >
> 
> 
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-- 
cheers,
Vadi

Query in C

[avinash pawar]

Hello Everyone ,

   Can anyone of you please tell me..

       what does extern "C" int func(int *,foo) accomplish ?

   waiting for your reply.

regards,
Avinash

Re: Query in C

[Steve Graegert]

On 8/1/05, avinash pawar <lkmails@gmail.com> wrote:
> Hello Everyone ,
> 
>   Can anyone of you please tell me..
> 
>       what does extern "C" int func(int *,foo) accomplish ?
> 

When using existing C headers that already conform to ANSI C in C++
they need to be slightly modified to enable proper linkage for the
language and to ensure that C++ keywords are not used as identifiers.

This means that you can use C headers in C++ projects in the following way:

#ifdef __cplusplus
       extern "C" {
#endif
...
int func(int *,foo);
...
#ifdef __cplusplus
       }
#endif

Code placed between the two ifdefs is either linked as C or C++.  The
__cplusplus macro is usually predefined in appropriate system headers.

To answer your question: when a routine will be called from another
language (here C is called from C++) it should be declared in C++ as

extern "C" int func(int *,foo);

The extern "C" causes the routine to have a so called 'unmangled' name
that can be refered to not only from C but also from Fortran or Cobol.
 Without extern "C" the routine will get a link 'mangled' link name
like func__abc.

Regards

        \Steve

-- 

Steve Graegert
Software Consultancy
Mobile: +49 (176)  21248869   
Office: +49 (9131) 7126409