[Objective-C++]Why assigning object to BOOL type variable is allowed in 64bit but not in 32bit

The following code in ViewController.mm, would be compiled successfully(without any warning or error) in 64 bit environment.

- (void)viewDidLoad {

    [super viewDidLoad];

    BOOL var = [[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

    NSLog(@"%d", var);

}

But when I change the running target to a 32 bit device(e.g, iPhone 5), it show me error like this:

 Cannot initialize a variable of type 'BOOL' (aka 'signed char') with an rvalue of type 'id _Nullable'

I do know this assignment is wroing, but why it allowed in first situation?

asked Nov 20 '18 at 2:11

Jintao Ou

11017

add a comment |

The following code in ViewController.mm, would be compiled successfully(without any warning or error) in 64 bit environment.

- (void)viewDidLoad {

    [super viewDidLoad];

    BOOL var = [[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

    NSLog(@"%d", var);

}

But when I change the running target to a 32 bit device(e.g, iPhone 5), it show me error like this:

 Cannot initialize a variable of type 'BOOL' (aka 'signed char') with an rvalue of type 'id _Nullable'

I do know this assignment is wroing, but why it allowed in first situation?

asked Nov 20 '18 at 2:11

Jintao Ou

11017

add a comment |

The following code in ViewController.mm, would be compiled successfully(without any warning or error) in 64 bit environment.

- (void)viewDidLoad {

    [super viewDidLoad];

    BOOL var = [[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

    NSLog(@"%d", var);

}

But when I change the running target to a 32 bit device(e.g, iPhone 5), it show me error like this:

 Cannot initialize a variable of type 'BOOL' (aka 'signed char') with an rvalue of type 'id _Nullable'

I do know this assignment is wroing, but why it allowed in first situation?

asked Nov 20 '18 at 2:11

Jintao Ou

11017

The following code in ViewController.mm, would be compiled successfully(without any warning or error) in 64 bit environment.

- (void)viewDidLoad {

    [super viewDidLoad];

    BOOL var = [[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

    NSLog(@"%d", var);

}

But when I change the running target to a 32 bit device(e.g, iPhone 5), it show me error like this:

 Cannot initialize a variable of type 'BOOL' (aka 'signed char') with an rvalue of type 'id _Nullable'

I do know this assignment is wroing, but why it allowed in first situation?

objective-c c++11 32bit-64bit objective-c++

asked Nov 20 '18 at 2:11

Jintao Ou

11017

asked Nov 20 '18 at 2:11

Jintao Ou

11017

asked Nov 20 '18 at 2:11

Jintao Ou

11017

asked Nov 20 '18 at 2:11

Jintao Ou

11017

asked Nov 20 '18 at 2:11

Jintao Ou

11017

add a comment |

3 Answers
3

active

oldest

votes

For 64-bit iOS, the BOOL type uses the C99 _Bool type (sometimes also available as bool). That type is defined to only have two values, 0 or 1. Assigning any other value to a variable of that type causes it to take on the value 1. (That is, all non-zero values become 1.)

So, the assignment won't truncate the bitwise value, potentially converting a non-zero value to zero. Therefore, it's "safe" in a certain respect and there's no cause for a warning. (It might still be surprising for a naive developer who didn't understand the difference between an object's pointer and its value, as other answers have addressed, but that's a different thing.)

edited Nov 20 '18 at 21:38

answered Nov 20 '18 at 4:41

Ken Thomases

69.5k669106

well that isn't the case here I will put a test on my answer.

– Grady Player
Nov 20 '18 at 21:01

actually the simplest example would be NSLog(@"%d",(BOOL)256);

– Grady Player
Nov 20 '18 at 21:04

@GradyPlayer, it's different between macOS and iOS. See /usr/include/objc/objc.h where it determines the default setting for OBJC_BOOL_IS_BOOL.

– Ken Thomases
Nov 20 '18 at 21:37

ok that may be... I would argue that it is still bad if it isn't guaranteed at a language level... I mean if I made the counter argument I would be downvoted to death...

– Grady Player
Nov 20 '18 at 22:10

1

@GradyPlayer The question was about why the compiler complained in one case (32-bit) but not the other (64-bit), not how to code it correctly. Nobody's saying that the code was good. Even the OP stated that the original code was buggy and they understood why.

– Ken Thomases
Nov 20 '18 at 23:51

add a comment |

The error says that you are assigning an object to a variable of type BOOL. To resolve it, you need to convert object returned from objectForKey: to a BOOL variable by using boolValue.

BOOL var = [[[NSUserDefaults standardUserDefaults] objectForKey:@"foo"] boolValue];

answered Nov 20 '18 at 4:06

trungduc

8,37531239

add a comment |

your code:
BOOL var = [[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

is assigning an object's address to essentially an int of some size...

This is almost always not what you want. You probably want:
BOOL var = [[[NSUserDefaults standardUserDefaults] objectForKey:@"foo"]boolValue];

If you do want to assign based on the presence of that object you could do:
BOOL var = !![[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

The reason is that if the bottom 8 bits of the address were to happen to all be 0's it could be a valid object, but would be a false value, which would be the result of the truncated assignment.

int main(int argc, const char * argv) {



    BOOL b = 2;

    if (b == YES)

    {

        NSLog(@"I guess you are right");

    }else{

        NSLog(@"nope");

    }

prints: nope

edited Nov 20 '18 at 21:02

answered Nov 20 '18 at 4:13

Grady Player

12.1k14168

add a comment |

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

edited Nov 20 '18 at 21:38

answered Nov 20 '18 at 4:41

Ken Thomases

69.5k669106

well that isn't the case here I will put a test on my answer.

– Grady Player
Nov 20 '18 at 21:01

actually the simplest example would be NSLog(@"%d",(BOOL)256);

– Grady Player
Nov 20 '18 at 21:04

@GradyPlayer, it's different between macOS and iOS. See /usr/include/objc/objc.h where it determines the default setting for OBJC_BOOL_IS_BOOL.

– Ken Thomases
Nov 20 '18 at 21:37

ok that may be... I would argue that it is still bad if it isn't guaranteed at a language level... I mean if I made the counter argument I would be downvoted to death...

– Grady Player
Nov 20 '18 at 22:10

1

@GradyPlayer The question was about why the compiler complained in one case (32-bit) but not the other (64-bit), not how to code it correctly. Nobody's saying that the code was good. Even the OP stated that the original code was buggy and they understood why.

– Ken Thomases
Nov 20 '18 at 23:51

add a comment |

edited Nov 20 '18 at 21:38

answered Nov 20 '18 at 4:41

Ken Thomases

69.5k669106

well that isn't the case here I will put a test on my answer.

– Grady Player
Nov 20 '18 at 21:01

actually the simplest example would be NSLog(@"%d",(BOOL)256);

– Grady Player
Nov 20 '18 at 21:04

@GradyPlayer, it's different between macOS and iOS. See /usr/include/objc/objc.h where it determines the default setting for OBJC_BOOL_IS_BOOL.

– Ken Thomases
Nov 20 '18 at 21:37

ok that may be... I would argue that it is still bad if it isn't guaranteed at a language level... I mean if I made the counter argument I would be downvoted to death...

– Grady Player
Nov 20 '18 at 22:10

1

@GradyPlayer The question was about why the compiler complained in one case (32-bit) but not the other (64-bit), not how to code it correctly. Nobody's saying that the code was good. Even the OP stated that the original code was buggy and they understood why.

– Ken Thomases
Nov 20 '18 at 23:51

add a comment |

edited Nov 20 '18 at 21:38

answered Nov 20 '18 at 4:41

Ken Thomases

69.5k669106

edited Nov 20 '18 at 21:38

answered Nov 20 '18 at 4:41

Ken Thomases

69.5k669106

edited Nov 20 '18 at 21:38

answered Nov 20 '18 at 4:41

Ken Thomases

69.5k669106

answered Nov 20 '18 at 4:41

Ken Thomases

69.5k669106

answered Nov 20 '18 at 4:41

Ken Thomases

69.5k669106

well that isn't the case here I will put a test on my answer.

– Grady Player
Nov 20 '18 at 21:01

actually the simplest example would be NSLog(@"%d",(BOOL)256);

– Grady Player
Nov 20 '18 at 21:04

@GradyPlayer, it's different between macOS and iOS. See /usr/include/objc/objc.h where it determines the default setting for OBJC_BOOL_IS_BOOL.

– Ken Thomases
Nov 20 '18 at 21:37

ok that may be... I would argue that it is still bad if it isn't guaranteed at a language level... I mean if I made the counter argument I would be downvoted to death...

– Grady Player
Nov 20 '18 at 22:10

1

@GradyPlayer The question was about why the compiler complained in one case (32-bit) but not the other (64-bit), not how to code it correctly. Nobody's saying that the code was good. Even the OP stated that the original code was buggy and they understood why.

– Ken Thomases
Nov 20 '18 at 23:51

add a comment |

well that isn't the case here I will put a test on my answer.

– Grady Player
Nov 20 '18 at 21:01

actually the simplest example would be NSLog(@"%d",(BOOL)256);

– Grady Player
Nov 20 '18 at 21:04

@GradyPlayer, it's different between macOS and iOS. See /usr/include/objc/objc.h where it determines the default setting for OBJC_BOOL_IS_BOOL.

– Ken Thomases
Nov 20 '18 at 21:37

ok that may be... I would argue that it is still bad if it isn't guaranteed at a language level... I mean if I made the counter argument I would be downvoted to death...

– Grady Player
Nov 20 '18 at 22:10

1

@GradyPlayer The question was about why the compiler complained in one case (32-bit) but not the other (64-bit), not how to code it correctly. Nobody's saying that the code was good. Even the OP stated that the original code was buggy and they understood why.

– Ken Thomases
Nov 20 '18 at 23:51

well that isn't the case here I will put a test on my answer.

– Grady Player
Nov 20 '18 at 21:01

actually the simplest example would be NSLog(@"%d",(BOOL)256);

– Grady Player
Nov 20 '18 at 21:04

@GradyPlayer, it's different between macOS and iOS. See /usr/include/objc/objc.h where it determines the default setting for OBJC_BOOL_IS_BOOL.

– Ken Thomases
Nov 20 '18 at 21:37

ok that may be... I would argue that it is still bad if it isn't guaranteed at a language level... I mean if I made the counter argument I would be downvoted to death...

– Grady Player
Nov 20 '18 at 22:10

@GradyPlayer The question was about why the compiler complained in one case (32-bit) but not the other (64-bit), not how to code it correctly. Nobody's saying that the code was good. Even the OP stated that the original code was buggy and they understood why.

– Ken Thomases
Nov 20 '18 at 23:51

add a comment |

The error says that you are assigning an object to a variable of type BOOL. To resolve it, you need to convert object returned from objectForKey: to a BOOL variable by using boolValue.

BOOL var = [[[NSUserDefaults standardUserDefaults] objectForKey:@"foo"] boolValue];

answered Nov 20 '18 at 4:06

trungduc

8,37531239

add a comment |

The error says that you are assigning an object to a variable of type BOOL. To resolve it, you need to convert object returned from objectForKey: to a BOOL variable by using boolValue.

BOOL var = [[[NSUserDefaults standardUserDefaults] objectForKey:@"foo"] boolValue];

answered Nov 20 '18 at 4:06

trungduc

8,37531239

add a comment |

The error says that you are assigning an object to a variable of type BOOL. To resolve it, you need to convert object returned from objectForKey: to a BOOL variable by using boolValue.

BOOL var = [[[NSUserDefaults standardUserDefaults] objectForKey:@"foo"] boolValue];

answered Nov 20 '18 at 4:06

trungduc

8,37531239

The error says that you are assigning an object to a variable of type BOOL. To resolve it, you need to convert object returned from objectForKey: to a BOOL variable by using boolValue.

BOOL var = [[[NSUserDefaults standardUserDefaults] objectForKey:@"foo"] boolValue];

answered Nov 20 '18 at 4:06

trungduc

8,37531239

answered Nov 20 '18 at 4:06

trungduc

8,37531239

answered Nov 20 '18 at 4:06

trungduc

8,37531239

answered Nov 20 '18 at 4:06

trungduc

8,37531239

add a comment |

your code:
BOOL var = [[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

is assigning an object's address to essentially an int of some size...

This is almost always not what you want. You probably want:
BOOL var = [[[NSUserDefaults standardUserDefaults] objectForKey:@"foo"]boolValue];

If you do want to assign based on the presence of that object you could do:
BOOL var = !![[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

The reason is that if the bottom 8 bits of the address were to happen to all be 0's it could be a valid object, but would be a false value, which would be the result of the truncated assignment.

int main(int argc, const char * argv) {



    BOOL b = 2;

    if (b == YES)

    {

        NSLog(@"I guess you are right");

    }else{

        NSLog(@"nope");

    }

prints: nope

edited Nov 20 '18 at 21:02

answered Nov 20 '18 at 4:13

Grady Player

12.1k14168

add a comment |

your code:
BOOL var = [[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

is assigning an object's address to essentially an int of some size...

This is almost always not what you want. You probably want:
BOOL var = [[[NSUserDefaults standardUserDefaults] objectForKey:@"foo"]boolValue];

If you do want to assign based on the presence of that object you could do:
BOOL var = !![[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

The reason is that if the bottom 8 bits of the address were to happen to all be 0's it could be a valid object, but would be a false value, which would be the result of the truncated assignment.

int main(int argc, const char * argv) {



    BOOL b = 2;

    if (b == YES)

    {

        NSLog(@"I guess you are right");

    }else{

        NSLog(@"nope");

    }

prints: nope

edited Nov 20 '18 at 21:02

answered Nov 20 '18 at 4:13

Grady Player

12.1k14168

add a comment |

your code:
BOOL var = [[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

is assigning an object's address to essentially an int of some size...

This is almost always not what you want. You probably want:
BOOL var = [[[NSUserDefaults standardUserDefaults] objectForKey:@"foo"]boolValue];

If you do want to assign based on the presence of that object you could do:
BOOL var = !![[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

The reason is that if the bottom 8 bits of the address were to happen to all be 0's it could be a valid object, but would be a false value, which would be the result of the truncated assignment.

int main(int argc, const char * argv) {



    BOOL b = 2;

    if (b == YES)

    {

        NSLog(@"I guess you are right");

    }else{

        NSLog(@"nope");

    }

prints: nope

edited Nov 20 '18 at 21:02

answered Nov 20 '18 at 4:13

Grady Player

12.1k14168

your code:
BOOL var = [[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

is assigning an object's address to essentially an int of some size...

This is almost always not what you want. You probably want:
BOOL var = [[[NSUserDefaults standardUserDefaults] objectForKey:@"foo"]boolValue];

If you do want to assign based on the presence of that object you could do:
BOOL var = !![[NSUserDefaults standardUserDefaults] objectForKey:@"foo"];

The reason is that if the bottom 8 bits of the address were to happen to all be 0's it could be a valid object, but would be a false value, which would be the result of the truncated assignment.

int main(int argc, const char * argv) {



    BOOL b = 2;

    if (b == YES)

    {

        NSLog(@"I guess you are right");

    }else{

        NSLog(@"nope");

    }

prints: nope

edited Nov 20 '18 at 21:02

answered Nov 20 '18 at 4:13

Grady Player

12.1k14168

edited Nov 20 '18 at 21:02

answered Nov 20 '18 at 4:13

Grady Player

12.1k14168

answered Nov 20 '18 at 4:13

Grady Player

12.1k14168

answered Nov 20 '18 at 4:13

Grady Player

12.1k14168

add a comment |

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