Type conflicts

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2 total messages Started by Erik Oestlyngen Fri, 23 Feb 1996 19:45

#3430

Author: Erik Oestlyngen
Date: Fri, 23 Feb 1996 19:45

64 lines
1899 bytes

Hi.

I'm doing working with a project trying to make a model for namespace
structure of C++ programs, and make a visualization of it. (by the
way, does anyone know of any interesting stuff on the net in this
context ?)

Anyhow, i've got this little problem:

When i define two different structs with the same name in two
different files, my compiler don't complain. I can then use the struct
as input parameter for a function in one file, and from the other send
the different struct into the function. The function will then get
an other input type than it expects.

What does the ansi-C++ standard say about this?


Example:
========

File1:

struct a {
 int x;
};

extern void f(struct a);

void main(void)
{
 struct a str;

 str.x=1;

 f(str);
}

---------------------

File2:

struct a {
 long x;
};

void f(struct a astr)
{
  astr.x+=2;    // crash, bang, crunch
}

-- 
--Erik Oestlyngen

---------------------------------------------------------------
erikoest@idt.unit.no      URL http://www.idt.unit.no/~erikoest/


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Re: Type conflicts

#3432

Author: Steve Clamage
Date: Fri, 23 Feb 1996 22:38

26 lines
1629 bytes

In article fsf@pil.idt.unit.no, erikoest@idt.unit.no (Erik Oestlyngen) writes:
>
>When i define two different structs with the same name in two
>different files, my compiler don't complain. I can then use the struct
>as input parameter for a function in one file, and from the other send
>the different struct into the function. The function will then get
>an other input type than it expects.

>What does the ansi-C++ standard say about this?

The One-Definition Rule says in part that two types with the same name
in the same scope must have the same definition.

Your code violates the One-Definition Rule, and has undefined behavior.
The compiler is not required to diagnose the error.

---
Steve Clamage, stephen.clamage@eng.sun.com


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