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Re: Calling a function with a float argument modifies caller's state.

From: Andrew Haley <aph at redhat dot com>
To: Jeff B <a dot GNUbie at myLetters dot US>
Cc: Ángel González <keisial at gmail dot com>, David Brown <david at westcontrol dot com>, gcc-help at gcc dot gnu dot org
Date: Wed, 22 Aug 2012 08:50:50 +0100
Subject: Re: Calling a function with a float argument modifies caller's state.
References: <50329C63.8080809@myLetters.US> <50332D55.10002@westcontrol.com> <50339936.3070805@gmail.com> <5033C827.1090704@myLetters.US>

On 08/21/2012 06:40 PM, Jeff B wrote:
> (int)floatVarA = 0.000000            <<=== initial value 0??

The initial value is zero because there is garbage in Float Register 0.

> floatVarA = 1234.000000

Now Float Register 0 contains 1234.0 .

> (int)floatVarA = 1234.000000     <<=== changed

Which gets printed out.

> floatVarB = 5678.000000

Now Float Register 0 contains 5678.0 .

> (int)floatVarA = 5678.000000    <<=== changed again

Which gets printed out.

> floatVarA = 1234.000000

etc...

Moral: undefined behaviour can do anything.

Andrew.

Follow-Ups:
- Re: Calling a function with a float argument modifies caller's state.
  - From: Jeff B

References:
- Calling a function with a float argument modifies caller's state.
  - From: Jeff B
- Re: Calling a function with a float argument modifies caller's state.
  - From: David Brown
- Re: Calling a function with a float argument modifies caller's state.
  - From: Ángel González
- Re: Calling a function with a float argument modifies caller's state.
  - From: Jeff B

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