From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steve Graegert Subject: Re: Variable to sizeof function. Date: Sat, 16 Jul 2005 09:04:36 +0200 Message-ID: <6a00c8d505071600046bc58cd7@mail.gmail.com> References: <6a00c8d505071515355f041394@mail.gmail.com> <20050716064421.85333.qmail@web31901.mail.mud.yahoo.com> Reply-To: Steve Graegert Mime-Version: 1.0 Content-Transfer-Encoding: 7BIT Return-path: In-Reply-To: <20050716064421.85333.qmail@web31901.mail.mud.yahoo.com> Content-Disposition: inline Sender: linux-c-programming-owner@vger.kernel.org List-Id: Content-Type: text/plain; charset="us-ascii" To: Vikas S Cc: Rechberger Markus , linux-c-programming@vger.kernel.org On 7/16/05, 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. Wow, that's a lot of work :-) > a) You are right. > b) Yes. I want to pass a structure name. ie, make sizeof > accept a variable. > > Is this impossible? I guess you want to save typing and be able to query the size of a particular structure dynamically simply by specifying its name (the variable name) on the command line. Unfortunately there is no mechanism known to me that allows it. The C programming language provides no way to do some name to variable mapping. A couple of days ago, one has asked how to obtain the number and names of function arguments dynamically which is a problem of the same kind. What you are looking for is some kind of reflection to fetch type information at run-time. You can try to set up a table with pointers to every structure and use this entry to query the size. I don't see another solution. Regards \Steve > Thanks, > Vikas > > --- Steve Graegert wrote: > > > On 7/15/05, Vikas S 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 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 wrote: > > > > > Vikas, > > > > > > > > > > On 7/15/05, Vikas S 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. > > > http://promotions.yahoo.com/new_mail > > > - > > > 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 > > > > > > > > > -- > > ______________________________________ > > 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 > > - > > 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!? > Tired of spam? Yahoo! Mail has the best spam protection around > http://mail.yahoo.com > -- ______________________________________ 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