Strcmp() returns wrong value

Dev Shed Forums Sponsor:

January 11th, 2013, 11:06 AM

so.very.tired

Contributing User

Join Date: Nov 2012

Posts: 111

Time spent in forums: 1 Day 4 h 5 m 15 sec
Reputation Power: 1

Strcmp() returns wrong value

here's the code for example:

Code:

int main()
{
	char str1[15], str2[15];

	printf("Enter first string:");
	scanf("%s", str1);
	printf("Enter second string:");
	scanf("%s", str2);

	printf("%d", strcmp(str1,str2));
}

here's the output:

Code:

Enter first string: hello
Enter second string: world
-15

what's wrong with it?
why wouldn't it return 1 as it should?

January 11th, 2013, 11:56 AM

salem

Contributed User

Join Date: Jun 2005

Posts: 3,834

Folding Points: 153 Folding Title: Novice Folder

Time spent in forums: 2 Months 3 Weeks 2 Days 14 h 28 m 7 sec
Reputation Power: 1774

Why would you expect it to return 1?

The spec for strcmp reads
<0 if a is before b
>0 if a is after b
== 0 if they're the same

You have -15, indicating "hello" is before "world" (which it is).

__________________
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper

January 12th, 2013, 04:27 AM

so.very.tired

Contributing User

Join Date: Nov 2012

Posts: 111

Time spent in forums: 1 Day 4 h 5 m 15 sec
Reputation Power: 1

for some reason (maybe i read it somwhere) i thought that if it reurns 1 then first string is before second string, 0 if they're the same, and -1 if second string is before the first string...

thank you!

January 13th, 2013, 12:00 AM

requinix

Still alive

Join Date: Mar 2007

Location: Washington, USA

Posts: 12,680

Folding Points: 417516 Folding Title: Super Ultimate Folder - Level 1

Time spent in forums: 5 Months 1 Week 4 Days 1 h 55 m 14 sec
Reputation Power: 8969

Send a message via Google Talk to requinix

Some languages have a comparison function like strcmp but specifically return -1, 0, or 1. The C function returns the difference between the two strings (as you may have realized) and thus merely guarantees a negative, zero, or positive number.
As for returning 1/positive if the first string < second string, I'm not sure where you got that from. No offense but you might just be remembering it backwards.

__________________
Site rules and FAQ | Project Suggestions | mod_rewrite guide | PHP New User Guide and FAQ - PHP Stickies | Regex Resources

January 13th, 2013, 03:25 AM

clifford

Contributing User

Join Date: Aug 2003

Location: UK

Posts: 4,806

Time spent in forums: 1 Month 2 Days 17 h 19 m 38 sec
Reputation Power: 1800

Quote:

Originally Posted by so.very.tired

for some reason (maybe i read it somwhere) i thought that if it reurns 1 then first string is before second string, 0 if they're the same, and -1 if second string is before the first string...

Reading it somewhere is good; but perhaps you should have checked before posting a question. There are many sources for documentation of teh standard library; here's one. If the documentation only guarantees <0, 0, or >0, even if you observe -1, 0 and 1 in any particular implementation, you cannot assume that that will always be the case.

In this case -15 is the result of performing 'w' - 'h' which gives a clue as to how strcmp() is working in this case. It is simply performing a numerical comparison of the character codes, and returns the difference between the first two non-matching characters.

Strcmp() returns wrong value

Developer Shed Advertisers and Affiliates