Bug of the day

Ravi Bhavnani

Does that even compile? /ravi

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anton_l

It seems that problem is in semicolon after "if" statement. DoSomeThing will be fired any time the code executes.

YvesDaoust

This is one of the dangers of C syntax (and friends). That's the price you pay for willing conciseness. Block-only statements like VB's

If Condition Then
Statement
End If

or Modula's

IF Condition THEN
Statement
END

are safer.

Bernhard Hiller

Oh no, you misunderstood the guy who wrote that piece of code. Never did he intend that DoSomeThing() is executed only when some codition is true. He just wanted to make his colleagues (who'll have to maintain his buggy code after he quit his job) believe so.

R Erasmus

Seems like a new style of comment... if you're compiler doesn't support any comments. ;P

"Program testing can be used to show the presence of bugs, but never to show their absence." << please vote!! >>

Klaus Werner Konrad

Wich compiler ?

while (*dest++ = *source++);

is completely correct, isn't it ?

BobJanova

It's a warning, not an error, for that reason. This was back when I used Zortech's ANSI C compiler.

Gary Wheeler

Or Pascal:

if condition then
begin
DoStuff();
end
else
begin
DoOtherStuff();
end;

Sort an 'are you sure?' prompt for every single conditional. :rolleyes:

Software Zen: delete this;

BobJanova

Can't you do if condition then one-statement else other-statement though if you don't need a block?

Gary Wheeler

Yes, but I've always hated doing those, unless you write it on a single line:

if condition then DoSomething() else DoOtherThing();

That's the only way in my mind to avoid stupid mistakes like this:

if condition then
DoThing1();
DoThing2();
DoThing3();
MainStuff();

DoThing2() and DoThing3() look like they're part of the if, but they're not. I do the same thing in C-style languages. If an if-statement occupies more than one line, it gets braced.

Software Zen: delete this;

Fabio Franco

I had to read it three times before spotting the problem. Go bugged by the fact that DoSomeThing didn't have parenthesis.

To alcohol! The cause of, and solution to, all of life's problems - Homer Simpson ---- Our heads are round so our thoughts can change direction - Francis Picabia

BobJanova

I agree and would always put that on a single line.

gervacleto

Me too. I didn't see the semicolon until I review it two or three times. So maybe it is not a trap but a genuine bug. Some times you check your code 10 times and do not see this kind of bugs. :-\

You may forget having good days, just because you are remembering the past or thinking too much about the future. Live now and enjoy the moment!!

Fabio Franco

Tell me about it. I'm specially vulnerable to problems that are right in front of my face. I do this too often: :doh: Maybe it's my short span of attention.

To alcohol! The cause of, and solution to, all of life's problems - Homer Simpson ---- Our heads are round so our thoughts can change direction - Francis Picabia

gervacleto

This errors can be present in C like language. The last only in C# This one is usual (very)

if(Something)
One();
two();
...

Of course only One() is inside the if(), but it seems that the other two instructions are inside also. I did fall in this bug many times until I decided to enclose into curly braces any if() or loop with one or more instructions. It could increase the number of lines, but, for sure, decrease the bugs. Other one:

bool MyBoolValue = true;

if(MyBoolValue = false){
... SomeStuff ...
}

Maybe the compiler throws a warning, but this statement is valid. Surely is not what you want to do because you have omitted one equal sign:

if(MyBoolValue == false)...

I have no solution to this one, but to check again :sigh: Of course the comparison is not necessary, because MyBoolValue is true or false per se. ;)

if(MyBoolValue)...

for(int i = 0; i < MyArray.GetUpperBound(0); i++){
SomeStuff....
}

You must remember that GetUpperBound(0) does not start in '0' but in '1', because is the number of elements not the dimensions of the array so it must be:

for(int i = 0; i <= MyArray.GetUpperBound(0); i++)

I will try to remember more "Mistakes" that are common for me, but for sure here are more qualified people to show you many more.

You may forget having good days, just because you are remembering the past or thinking too much about the future. Live now and enjoy the moment!!

Pablo Aliskevicius

I usually prefer:

if (42 == ComputeSomeThing(x)) {
//...
}

This one avoids the = against == pit. Another thing I do: my IDE is configured to show operators (like '(){};,+-=...') in color, so they are a bit harder to miss (like the original example). There are two other tools that can help with this: compiler warnings, and static code analysis. JM2B,

Pablo. "Accident: An inevitable occurrence due to the action of immutable natural laws." (Ambrose Bierce, circa 1899).

Fabio Franco

gervacleto wrote:

if(Something) One(); two(); ...

This can also happen in C#, but auto indent of Visual Studio makes you less likely to fall in this trap.

gervacleto wrote:

if(MyBoolValue = false){

This happened to me several times and the warning saved. I always pay attention to warnings.

gervacleto wrote:

if(MyBoolValue)

I do not consider this a bug, it is actualy a coding style. I do it myself.

gervacleto wrote:

for(int i = 0; i <= MyArray.GetUpperBound(0); i++)

Never used this construct, so I wouldn't know. But will keep my mind to it in case I run into this. Thanks!

To alcohol! The cause of, and solution to, all of life's problems - Homer Simpson ---- Our heads are round so our thoughts can change direction - Francis Picabia

Lost User

Quote:

If an if-statement occupies more than one line, it gets braced.

Maybe I'm naïve, but I thought everybody did that! :)

Gary Wheeler

I've worked with people who did this:

if condition
DoSomething();
else
{
DoOtherThing1();
DoOtherThing2();
}

or

if condition
{
DoSomething1();
DoSomething2();
}
else
DoOtherThing();

Both of which give me the creeping heebie-jeebies.

Software Zen: delete this;

MainFrameMan_ALIVE_AND_WELL

the semi-colon on the end of the conditional, the block will always execute. DoSomething is in its own little world and will always execute. C# will just raise a warning on the conditional but will not compile with the DoSomeThing becuse it is not a method or an assignment. But, what if it is not C# compiler, then there could be compilers that would allow this and it would be worthless code, i still use Crimson, NotePad, etc to write code. Either to many semi colons or not enough !!