#if TRUE vs #if YES vs #if 1 are different from Objective-C?
Mhm ... I'm not really an objective-c person, I personally like C ++ better, but let me try to answer you anyway.
if 1
The compiler, after all, like everything in computers, runs on zeroes and in one. When you write an "if 1" statement in your code, it will always do it like any other number you can put there, that is, other than zero. This is because the bit representation of 0 in bytes is "00000000", which represents a negative value. Because of this, the most basic statement you can make to make sure you have true, at the code level and at the compiler level, is if (a nonzero number here) that will always be true.
if TRUE
true is a stored word in the compiler that eventually becomes 1. So if (true) always works; naturally, I guess it takes a while for the compiler to parse it, but that's pretty much the only difference, and it's pretty minor.
, If yes
The compiler does not know the word "Yes". Thus, it automatically accepts its parameter and tries to find if it was previously declared. When it discovers that you haven't defined it before in your program, it puts the default in the if statement - which is false; Thus, the command fails.
Hope I helped :)
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If a term is YES
either undefined or defined as 0
, it #if
will never become true.
If the identifier is not defined, it is treated as 0
. Therefore, the preprocessor will see
#if 0
NSLog(@"print YES");
#endif
Which also won't execute the command NSLog
.
The code in the statement #if
will only be executed ifYES
- identified and
- set to non-zero
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It's hard to believe when you think about it, but the C programming language didn't have a boolean type until 1998. Programmers developed their own solutions, and over time it became common to use int with 0 for no. When the boolean was added at the end, it was like a true first class boolean type. This means that it can only store the values 0 and 1.read more here
You can check it out for yourself in objC with something like this.
bool foo = 55;
NSLog ((foo) ? (@"foo, it is true") :(@"no, foo is false") ); //will log true..
NSLog (@"foo int value", (int)foo ); // will log 1
now bool uses the full 8 bits, it's just (I think) that only the first (or the last depending on your / endian -ness architecture) is ever written to / read from.
ObjectiveC has now been running for much longer than 1998. So BOOL is actually older than bool! This is why it was always defined as char. It is actually capable of storing values between -127 and 128. Again you can check this in Xcode
BOOL bar = 55;
NSLog ((bar) ? (@"bar, it is true too!") :(@"no, bar neither") );
//will again log true..
NSLog (@"bar int value", (int)bar );
// will log 55 on 32bit builds but 1 on 64bit builds
Yes, but not always, as you can see. In 64-bit OBJC, BOOL is defined as bool!
from objc.h
#if !defined(OBJC_HIDE_64) && TARGET_OS_IPHONE && __LP64__
typedef bool BOOL;
#else
typedef signed char BOOL;
// BOOL is explicitly signed so @encode(BOOL) == "c" rather than "C"
// even if -funsigned-char is used.
#endif
Because of bool and BOOL messy legacy in C and objC, truth tested for YES or true is not always 100% reliable. Instead, I recommend that you check for! False or! NO. Sounds funny?
heres a little blog about this i found on a big ranch nerd
PS I totally understand what you are talking about compiler conditions, but you marked it objC :)
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