please wait
if(!strcmp.....
Mar 19, 2012 at 3:29pm
This is making me crazy. This is the syntax I'm dealing with, and I just can't decide whether this statement results in 'true' or 'false'. I thought I understood this, but if I understand this correctly, then the code is 'wrong', or at least it definitely doesn't make sense to me.
if (!strcmp(str1, str2))
I understand(I think) that strcmp returns 0 if the strings are equal, and I understand(I think) that the ! is 'not' or reversing the result. Is that correct?
- So, if str1 = str2, then the strcmp returns 0, and the ! reverses that and makes it a 1, returning 'false' to the 'if'?
- and, if str1 <> str2, then the strcmp returns 1, and the ! reverses that and makes it be 0, returning 'true' to the 'if'?
- and then, since the if statement executes the subsequent actions only if true, then the subsequent actions would only be executed if str1 <> str2?
My problem is that the subsequent statement only makes sense if it's being executed when str1 = str2.
Help.
if (!strcmp(str1, str2))
I understand(I think) that strcmp returns 0 if the strings are equal, and I understand(I think) that the ! is 'not' or reversing the result. Is that correct?
- So, if str1 = str2, then the strcmp returns 0, and the ! reverses that and makes it a 1, returning 'false' to the 'if'?
- and, if str1 <> str2, then the strcmp returns 1, and the ! reverses that and makes it be 0, returning 'true' to the 'if'?
- and then, since the if statement executes the subsequent actions only if true, then the subsequent actions would only be executed if str1 <> str2?
My problem is that the subsequent statement only makes sense if it's being executed when str1 = str2.
Help.
Mar 19, 2012 at 3:34pm| - So, if str1 = str2, then the strcmp returns 0, and the ! reverses that and makes it a 1, returning 'false' to the 'if'? |
No. 1 is TRUE, not false.
Mar 19, 2012 at 3:41pm
Also strcmp() returns either 0 or an positive integer, depending on if str1 matches str2, or where the first inconstant character is.
!(int) any non-zero integer returns false, and !(0) returns true.
!(int) any non-zero integer returns false, and !(0) returns true.
Last edited on Mar 19, 2012 at 3:43pm
Mar 19, 2012 at 3:55pm| - So, if str1 = str2, then the strcmp returns 0, and the ! reverses that and makes it a 1, returning 'false' to the 'if'? No. 1 is TRUE, not false. |
That confuses me. If the ! were not there, and it just read:
if(strcmp(str1, str2))
Wouldn't that be true? Or, does the 0 actually return a false to the 'if' statement, and a 1 result in a 'true'?
Maybe that's where the root of my confusion lies.
I've been assuming that a 0 = true, because I've also seen the following syntax:
if(strcmp(str1, str2) !=0)
{then do this}
{then do this}
And I thought the action would execute if the strings are not equal.
Mar 19, 2012 at 3:56pm| Also strcmp() returns either 0 or an positive integer, depending on if str1 matches str2, or where the first inconstant character is. |
Yes, I understand that, and I think it can return a negative integer if the first mismatched character str2 is greater than str1, right?
Mar 19, 2012 at 4:05pm
OK - I think I understand where my confusion is, if someone would verify this.
I've been thinking "it's true that string1 = string2, and strcmp returns 0 if they are equal, therefore, 0 must mean 'true'"
But, it seems perhaps that the problem is in my basic assumption, and that a 0 actually means 'false' for the other functions (or at least for the 'if).
I've been thinking "it's true that string1 = string2, and strcmp returns 0 if they are equal, therefore, 0 must mean 'true'"
But, it seems perhaps that the problem is in my basic assumption, and that a 0 actually means 'false' for the other functions (or at least for the 'if).
Mar 19, 2012 at 4:23pm
Think of strcmp not as "are these the same?" but as "what are the differences between these two?".
Mar 19, 2012 at 4:30pm| Think of strcmp not as "are these the same?" but as "what are the differences between these two?". |
oh, that makes perfect sense now!
Thank you so much!
Mar 19, 2012 at 4:32pm
Now, one more question.
Why would you use the syntax
if(!strcmp(str1,str2)
instead of
if(strcmp(str1,str2) = 0
or vice versa?
Why would you use the syntax
if(!strcmp(str1,str2)
instead of
if(strcmp(str1,str2) = 0
or vice versa?
Mar 19, 2012 at 4:37pm
Because you can't assign to the return value of a function if it is not a reference. Perhaps you meant ==? In that case, which is shorter to type?
|
|
Last edited on Mar 19, 2012 at 4:38pm
Mar 19, 2012 at 4:51pm| Because you can't assign to the return value of a function if it is not a reference. Perhaps you meant ==? In that case, which is shorter to type? |
yes, you're correct, I did mean ==.
and yes, the second one is 1 character shorter to type :)
Mar 19, 2012 at 4:59pm
you mean the first one is two characters shorter... it would be more if you actually care about spacing your operators.
Mar 19, 2012 at 5:06pm| you mean the first one is two characters shorter... it would be more if you actually care about spacing your operators. |
right :p
It's just that the second one seems SO much easier to read and understand. But I guess if you're coding all day long, every 2 characters count.
Mar 19, 2012 at 5:30pm
The first one is obfuscated.
strcmp)() compares two strings.
0 means equal
>0 means greater
<0 means lesser
That convention is also used in qsort()
| strcmp returns 0 if they are equal, therefore, 0 must mean 'true'" |
0 means equal
>0 means greater
<0 means lesser
That convention is also used in qsort()
Topic archived. No new replies allowed.