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[94.253.207.38]) by smtp.gmail.com with ESMTPSA id o8sm1842299ejj.102.2020.07.08.04.41.50 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 08 Jul 2020 04:41:51 -0700 (PDT) Date: Wed, 8 Jul 2020 13:41:49 +0200 From: Marko Turk To: rahul deshmukh Cc: freebsd-hackers@freebsd.org Subject: Re: strange output in c program Message-ID: <20200708114149.GA73229@vps.markoturk.info> References: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="rwEMma7ioTxnRzrJ" Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 4B1y813WTPz3xwN X-Spamd-Bar: ---- Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=none; spf=softfail (mx1.freebsd.org: 209.85.208.47 is neither permitted nor denied by domain of markoml@markoturk.info) smtp.mailfrom=markoml@markoturk.info X-Spamd-Result: default: False [-4.21 / 15.00]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RECEIVED_SPAMHAUS_PBL(0.00)[94.253.207.38:received]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; NEURAL_HAM_MEDIUM(-0.86)[-0.861]; NEURAL_HAM_LONG(-1.00)[-0.998]; TAGGED_RCPT(0.00)[]; MIME_GOOD(-0.20)[multipart/signed,text/plain]; PREVIOUSLY_DELIVERED(0.00)[freebsd-hackers@freebsd.org]; R_SPF_SOFTFAIL(0.00)[~all]; DMARC_NA(0.00)[markoturk.info]; RCVD_COUNT_THREE(0.00)[3]; TO_MATCH_ENVRCPT_SOME(0.00)[]; NEURAL_HAM_SHORT(-0.15)[-0.147]; RCPT_COUNT_TWO(0.00)[2]; RCVD_IN_DNSWL_NONE(0.00)[209.85.208.47:from]; SIGNED_PGP(-2.00)[]; FREEMAIL_TO(0.00)[gmail.com]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+,1:+,2:~]; ASN(0.00)[asn:15169, ipnet:209.85.128.0/17, country:US]; RCVD_TLS_ALL(0.00)[]; RWL_MAILSPIKE_POSSIBLE(0.00)[209.85.208.47:from] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 08 Jul 2020 11:41:54 -0000 --rwEMma7ioTxnRzrJ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Jul 08, 2020 at 05:04:26PM +0530, rahul deshmukh wrote: > Hi Team, > i was learning c programming and came across a very strange output. kindly > someone please guide me if i am missing anything. >=20 > rdx@FreeBSD:~/Projects/Clang/chapter3 % uname -a > FreeBSD FreeBSD 12.1-RELEASE FreeBSD 12.1-RELEASE r354233 GENERIC amd64 > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > rdx@FreeBSD:~/Projects/Clang/chapter3 % cat example6.c > #include > int main() > { > int a =3D 300, b, c; > if(a >=3D 400) > { > printf("shouldn't print\n"); > b =3D 300; > } > c=3D200; > printf("%d %d\n", b, c); > return 0; > } > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D > rdx@FreeBSD:~/Projects/Clang/chapter3 % make example6 > `example6' is up to date. > rdx@FreeBSD:~/Projects/Clang/chapter3 % ./example6 > 300 200=3D=3D> should be garbage value instead of 300? The behaviour is undefined so anything can happen. Even different optimization flags can change the value printed. 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