Simple if statement question

[Harrington]

This may be trivial, but something I haven't seen before... in some existing code I came across a statement (where temp_calc is a char variable):

if ( !(temp_calc, "MULTI_TEST&quot )...

What does the "(,)" operator do? Is it legal with two char types as shown in the above example?

Thanks in advance!

 

[xwb]

if ( !(temp_calc, "MULTI_TEST&quot )...

it is probably a coding bug. It is always true since !"MULTI_TEST" will never be 0. The comma is a statement separator like the semi-colon. In this case it takes the last expression after the comma. It is legal because C is an expression language. You see the use of the comma in the for statement

for (i = 0, j = 99; i > aaa && j < 0; i++, j--) ...

The very common comma coding bug is when people move from Pascal to C. Instead of

x[5][6]

they code

x[5,6]

which is perfectly legal: it just returns x[6].

 

[hnd]

An other possibility is the exclamation sign(!) has been redefined by the preprocessor to a function or a Macro. That makes not to much sense, but some programmers are very creative.

hnd
hasso55@yahoo.com

 

[Harrington]

Thanks guys!! I wasn't sure how it would evaluate (and why it compiled), but this makes perfect sense. I'm sure what they meant was:

if ( !strcmp(temp_calc, &quot;MULTI_TEST&quot )...

This wouldn't be the first bug I've seen in this code! At least now I can see what the effect of the current expression is on the downstream code.

Thanks again!

 

[xwb]

I don't know about you but I find

if (!strcmp(...)

a bit confusing as I initially read it to mean the strings are not equal (even after 15 years of C). Basically, the ! throws me. I normally prefer to code as

if (strcmp (...) == 0)

 

[Harrington]

Agreed 100%! I always err on the side of readability. In fact, some of this code I'm updating was full of &quot;negative logic&quot; which I've replaced. I don't like to have to stop and think about each expression when going through the code... I always use &quot;if (strcmp (...) == 0)&quot;...