true/false statements in if clause

Maximilien

TCPMem wrote:

if(true == a)

because if you type "=" instead of "==" the compiler will report an error. M.

Watched code never compiles.

Lost User

They are all largely a matter of style, although option 1 tends not to be used in C++ as most modern compilers tend to query expressions of the form:

if (a = true)

on the basis that it is probably a typo. The last form is quite acceptable although once again things have moved on with C++ and a might not be a bool type.

Just say 'NO' to evaluated arguments for diadic functions! Ash

David Crow

TCPMem wrote:

Why is more apropriate to write if(true == a)

Because the compiler will catch the error if you mistakingly use an assignment operator.

TCPMem wrote:

if(a) is avoidable. I mean not avoidable...

This is simply checking if a has a non-zero value (regardless of what type it is).

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Code o mat

i personally dislike

if (a)

because it isn't obvious at the very first look what exactly 'a' is, it could be a bool, an int, a pointer, an instance of a class with a bool operator, and it can be confusing if you are e.g. reading someone else's code and do not have an in-depth knowledge of what is what and why.

> The problem with computers is that they do what you tell them to do and not what you want them to do. < > "It doesn't work, fix it" does not qualify as a bug report. < > Amazing what new features none of the programmers working on the project ever heard of you can learn about when reading what the marketing guys wrote about it. <

Luc Pattyn

I mostly disagree with the others. 1. You need better identifier names. Then the short form is the right one:

if (printingToFile) printToFile();

2. it does not make sense comparing with true explicitly, as can be proven ex absurdo: If you think

if (a==true) ...

is any good, then the following is even better:

if ((a==true)==true) ...

3. when the variable's type is NOT boolean and you need an explicit constant value, then one can argue putting the constant first is safer, as it causes an error when accidentally = is used instead of ==. However, a decent compiler will generate a warning when you accidentally write:

if (myInteger=1) ...

:)

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fjdiewornncalwe

This was adopted as a standard some time ago by many developers for these statements because there was actually a time when the compiler would not have complained about

if( isThisCool = true )

but most certainly would have complained about

if( isThisCool = a )

so it was a little bit of a defensive coding mechanism. Nowadays, it really doesn't matter and I personally have gone to the

if( isThisCool )

syntax. It just reads nice that way.

CPallini

I don't agree with your point 2 proof (though it is clever). :)

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Aescleal

Generally prefer the third form - if someone needs reminding that a logical expression resolves to true (non-zero in older languages) or false (0 in older languages) in an algol derived language then they need a refresher. If you use decent names, know boolean algebra and wrap up complicated logical expressions in functions you can't go wrong. Or rather you probably won't go wrong, and if you did then direct comparison with true or false (either way around) isn't going to help you. Cheers, Ash

anonymouscodder

Actually if you use this form strictly to check if a is true instead of for example checking if the integer value is 0 this form is very clear.

Code o mat

As Richard said, it is a matter of style really. That form can also be very easily readable with well named variables, e.g:

if (noMoreItemsLeft) EndOfItems();

looks quite obvious when you read through the code, but

if (!ptrToNextItem) EndOfItems();

you have to 'analyze' this, if not ptrToNextItem, this means, if ptrToNextItem is zero, then... I also don't like situations like this:

class AClass
{
public:
int Integer;
bool Bool;

AClass(int i, bool b):Integer(i),Bool(b) {}
operator bool() const { return Bool; }
AClass &operator =(int i) { Integer = i; return *this; }
};
...
AClass A(0, true);
if (A) A = 3; //So here A's bool operator will be used and since it is true, A = 3 will run, however, A's
//integer value is 0, if we were to test for that, A = 3 wouldn't run. Ok, in this example
//it is quite obvious but imagine a big class with loads of operators and methods and this
//if embedded in a "busy" part of the code, "far far" away from the
//declaration of the class. If you were to "scan" through the code and see this you could
//think: 'what this does is making A's value 3 when A isn't 0, A is likely to be an
//integer'...
...

> The problem with computers is that they do what you tell them to do and not what you want them to do. < > "It doesn't work, fix it" does not qualify as a bug report. < > Amazing what new features none of the programmers working on the project ever heard of you can learn about when reading what the marketing guys wrote about it. <

Aescleal

I'd say that was more a criticism of the inappropriate use of operator overloading rather than a problem with not comparing the results of logical expressions to true and false. Cheers, Ash

Code o mat

I have seen this being done (not by me). Anyways, am just trying to say that "in my oppinion" simply writing if (whatever) doit(); isn't always completely clear and obvious. But i am repeating myself :) . This is indeed a question of style and personal oppinion, i am not saying it is good or bad, just sharing my point of view.

> The problem with computers is that they do what you tell them to do and not what you want them to do. < > "It doesn't work, fix it" does not qualify as a bug report. < > Amazing what new features none of the programmers working on the project ever heard of you can learn about when reading what the marketing guys wrote about it. <

Niklas L

Agreed 100%. Remember these ones:

BOOL bDoIt = ::ExternFunction();
if (bDoIt == TRUE)

where ExternFunction() according to documentation returns non-zero on success? It's not a matter of style. It's a matter of stupidity.

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PravinSingh

Niklas Lindquist wrote:

BOOL bDoIt = ::ExternFunction(); if (bDoIt == TRUE)

Niklas Lindquist wrote:

It's a matter of stupidity.

May be I'm being a bit stupid but, what exactly is "stupid" in the code above? if (bDoIt) would've looked nicer but if (bDoIt == TRUE) isn't bad either.

It's better to know some of the questions than all of the answers.
Pravin.

Niklas L

It's ultra-bad. Returning non-zero on success, might just as well mean returning 2, 3 or, God forbid, even 4. Comparing it to TRUE (i.e. 1) might not give the anticipated result. The only thing you can compare it to is FALSE, if (bDoIt != FALSE), would have been the correct usage. But that really doesn't help anyone, does it. Good naming removes the need for such constructs. It's about readability. Consider

if (signalIsOn) {}
if (signalIsOn == true) {}

The second construct is just plain silly, and actually reduces readability.

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PravinSingh

OK, now I get it. To be honest, I had never thought about this side effect. But, to me what seems to be the real problem here is the use of BOOL (which is essentially int)in place of bool. A bool bDoIt would have responded to any non-zero number by simply turning itself to true. Does that mean we should avoid using BOOL in general?

It's better to know some of the questions than all of the answers.
Pravin.

Niklas L

PravinSingh wrote:

the real problem here is the use of BOOL

I admit that this is slightly off topic, but still, I think it's worth mentioning. Avoiding BOOL in general is a good thing. But in reality, you would probably use a mix if you are hacking Windows API. The language evolves, but sadly, a lot of features are not used using excuses such as 'we need to handle an old code base' or 'we need to support an ancient compiler'. They might be valid excuses, but you could be stuck at that forever. Whenever possible, embrace what the technology gives. Also, embrace boolean algebra and proper naming :)

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