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From: barts@tekchips.UUCP
Newsgroups: comp.lang.c
Subject: Re: *\"LDA\" ok?
Message-ID: <1623@tekchips.TEK.COM>
Date: Sat, 22-Aug-87 21:31:48 EDT
Article-I.D.: tekchips.1623
Posted: Sat Aug 22 21:31:48 1987
Date-Received: Sun, 23-Aug-87 18:35:56 EDT
References: <8877@brl-adm.ARPA> <8088@mimsy.UUCP>
Reply-To: barts@tekchips.UUCP (Bart Schaefer)
Organization: Tektronix, Inc., Beaverton, OR.
Lines: 62

In article <8088@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:
]In article <8877@brl-adm.ARPA> ADLER1%BRANDEIS.BITNET@wiscvm.wisc.EDU writes:
]>I was trying to write a C program that would read MIX commands from
]>stdin. I also wanted to be able to verify that the string opcode
]>was actually internally equal to the string LDA....
]>        if (*opcode == *"LDA") printf("Gotcha!\n");
]>        else printf("No match...\n");
]No doubt this has already been answered in mail directed to
]adler1@brandeis.bitnet, but I want to expand on this a bit.
] [...]
]To compare the characters in `opcode' with the string "LDA" for
]equality, one should use
]	if (strcmp(opcode, "LDA") == 0)
]which is such a common idiom that old-time C programmers understand
]it at a glance.  It seems to come late to neophyte programmers,
]though, and it seems reasonable to ask why.
]
]Perhaps it is because other languages provide string comparison within
]the language itself:
] [...examples deleted...]
]Eventually it seems to dawn upon these programmers that
]	"LDA"
]generates an anonymous character array holding the letters L, D,
]A, and NUL (\0) and evaluates to the address of this array.  Then
]the purpose of strcmp() becomes clear, and they live happily ever
]after :-).
]
]All I want to know is this:  Why does it take so long for some
]programmers to see this, and how can we speed up the process?

I got my first C experience about 3 years ago when I was handed a code fragment
containing all sorts of marvelous UN*X ioctl() and fork()/wait() calls and told
to turn it into an interactive editor/parser.  Since then I have (hopefully)
improved in my understanding of C and my programming style, but my introoduction
to C is recent enough that I can comment on strcmp().

The single greatest problem I had in learning to use strcmp() is its return of
0 on "equality" of the strings.  I was expecting a boolean-valued comparison,
and this apparent sense-reversal (false on equality) threw more monkey wrenches
into my early programs than I would ever have believed.

Perhaps inexperienced programmers resort to trying direct comparisons ala
	string1 == string2	or	*string1 == *string2
after a few failures of
	if (strcmp(string1,string2)) print("They match!\n");
to do what they expect.

I'm not sure how to speed up learning the right way to use strcmp().  Maybe
inexperienced programmers should be encouraged to use something like
	#define streq(s1,s2)	(strcmp(s1,s2) == 0)
until they get used to non-boolean-valued comparisons.  I suppose, however,
that it could be argued that this will only delay understanding strcmp(), but
at least the novice will have a "function" that does what built-in equivalency
tests in other languages already do.

]-- 
]In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
]Domain:	chris@mimsy.umd.edu	Path:	seismo!mimsy!chris
-- 
Bart Schaefer
Oregon Graduate Center				...!tektronix!ogcvax!schaefer
Guest at Tekchips				...!tektronix!tekchips!barts