NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/8651

Text File | 1996-08-05 | 3.6 KB | 105 lines

Path: newshost.lanl.gov!tanmoy
From: [e-mail] (Tanmoy Bhattacharya)
Newsgroups: comp.lang.c
Subject: Re: Passing Structures As Pointers; Easy Question I think....
Date: 03 Mar 1996 19:43:27 GMT
Organization: Los Alamos National Laboratory
Message-ID: <[e-mail]>
References: <4hcov3$[e-mail]>
NNTP-Posting-Host: qcd.lanl.gov
Mime-Version: 1.0
Content-Type: text
In-reply-to: [e-mail]'s message of 3 Mar 1996 13:38:27 -0500

In article <4hcov3$[e-mail]>
[e-mail] (Razine) writes:

R: I recently ran into a problem passing a structure as a pointer to a
R: function.  I then wanted to pass a indivdual variable to another function
R: but it didnt work.  Here is a brief example.  Can anyone spot anything
R: wrong.
R:
R: typedef struct {
R:     char name[81];
R:     int address_num;
R: } person_rec;
R:
R:
R:
R: void main(void) {

main must be declared as returning int in a C program. The effect of
returning void is undefined in the C standard.

R:    person_rec thisuser;
R:
R:   display_person(&thisuser);

As display_person has not yet been declared, the compiler assumes it
is compatible with the declaration `int display_person()'. Your actual
definition actually returns void, so this assumption is wrong. As the
compiler makes a wrong assumption, no one can tell you what happens
from here on. (The compiler may document what happens, but it is
certainly not required to.) declare `void
display_person(person_rec*);' before trying to use it, or move the
definition to before the use.

As display_person does not initialize the record before using it, you
are using thisuser before initializing it. This is a disaster. I
assume this is only because you were trying to make things, short and
simple for us: please do not make things so short and simple that they
actually become wrong!

R:
R: }
R:
R: void display_address(int address) {
R:     printf("Adress Number is %d\r\n",address);

Use of \r in printf is almost certainly wrong. The C library is
supposed to put in the correct line terminator when you printf a \n.

R:     return;
R: }
R:
R: void display_person(person_rec *pr) {
R:
R:    printf("Persons Name : %s\r\n",pr->name);  /* another question why in
R: this instance would I have to use the -> operand? */

The operator -> means that the left operand is a pointer to a
struct. The . operator means that the left operand is a struct.

Remember %s assumes that the aaray of characters that you are sending
in (loose usage) is terminated by a '\0'. If the array is not
initialized, there is no guarantee what happens.

R:    display_address(pr->address_num);
R:
R: /* Basically I get an error on the line above, how would I just pass the
R: interger value contained in pr->address_num */

The call looks correct. What error do you get?

R:
R:    return;
R: }
R:
R:
R: I hope someone can help, I found a work around but it is sloppy and I want
R: to understand why, and what I am doing wrong.  Thanks
R:

Only if you show us a small complete compilable example with an
explanation of _what_ error you get when trying to compile or run it.

Cheers
Tanmoy
--
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