Check if string is null

doubty · 07-04-2009, 09:27 AM

Hi,

Can you tell me how to check if a string is null in C?

I tried p != '\0' doent seem to wrk though!

thanks

EVOEx · 07-04-2009, 09:35 AM

Do you want to test if a character array points to NULL or a string is empty? Your wording doesn't make much sense.

But the two I said:

Code:

p == NULL /* True if character array points to NULL */
!*p or *p == '\0' /* True if string empty */

flexo87 · 07-04-2009, 09:41 AM

Code:

char *p=NULL;
if (!p) printf("p is null");
else printf("p is not null");

keep in mind that if i didn't write the assignment (p=NULL) its value would be undefined and the if statement wouldn't work. in a string '\0' is the terminating null byte, you can check when a string is finished but you need to dereference the address:

Code:

char *p;
if (*p=='\0')...

Hope that helped

iMalc · 07-04-2009, 03:10 PM

Quote:

Originally Posted by doubty

Can you tell me how to check if a string is null in C?

I tried p != '\0' doent seem to wrk though!

It all depends on what you mean, and what p is declared as. That looks like an empty string check to me.
All types of strings in all languages can be "empty" but only some of them can also represent the concept of being "null".

07-04-2009, 09:27 AM	#1
doubty Registered User Join Date: Jun 2009 Posts: 39	Check if string is null Hi, Can you tell me how to check if a string is null in C? I tried p != '\0' doent seem to wrk though! thanks
doubty is offline

07-04-2009, 09:35 AM	#2
EVOEx Registered User Join Date: Oct 2008 Posts: 452	Do you want to test if a character array points to NULL or a string is empty? Your wording doesn't make much sense. But the two I said: Code: p == NULL /* True if character array points to NULL / !p or p == '\0' / True if string empty */
EVOEx is offline

07-04-2009, 09:41 AM	#3
flexo87 gcc -Wall -pedantic *.c Join Date: Jan 2009 Location: London Posts: 52	Code: char p=NULL; if (!p) printf("p is null"); else printf("p is not null"); keep in mind that if i didn't write the assignment (p=NULL) its value would be undefined and the if statement wouldn't work. in a string '\0' is the terminating null byte, you can check when a string is finished but you need to dereference the address: Code: char p; if (*p=='\0')... Hope that helped
flexo87 is offline

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