Question about creating a struct of flags in c++

[Plissken.s]

Is there an efficient way to create a struct of flag in C++?

I need to create a struct of boolean flag, like this:
struct testStruct {
bool flag1;
bool flag2;
bool flag3;
bool flag4;
bool flag5;
bool flag6;
bool flag7;
bool flag8;
bool flag9;
bool flag10;
bool flag11;
bool flag12;
bool flag13;
};

But if I do that, i print out the sizeof(), that struct and it is 13.
So i think the compile use 1 byte for each flag.

Is it possible to create a struct so that each flag uses only 1 bit.

Thank you.

[Victor Bazarov]

Pl********@gmai l.com wrote:

Is there an efficient way to create a struct of flag in C++?

I need to create a struct of boolean flag, like this:
struct testStruct {
bool flag1;
bool flag2;
bool flag3;
bool flag4;
bool flag5;
bool flag6;
bool flag7;
bool flag8;
bool flag9;
bool flag10;
bool flag11;
bool flag12;
bool flag13;
};

But if I do that, i print out the sizeof(), that struct and it is 13.
So i think the compile use 1 byte for each flag.

Is it possible to create a struct so that each flag uses only 1 bit.

Yes, read about bitfields. The syntax is the colon and the field width
after the name of the member, like

bool flag1:1;

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[Plissken.s]

On Oct 29, 11:10*pm, Victor Bazarov <v.Abaza...@com Acast.netwrote:

Plisske...@gmai l.com wrote:

Is there an efficient way to create a struct of flag in C++?

I need to create a struct of boolean flag, like this:
struct testStruct {
* *bool flag1;
* *bool flag2;
* *bool flag3;
* *bool flag4;
* *bool flag5;
* *bool flag6;
* *bool flag7;
* *bool flag8;
* *bool flag9;
* *bool flag10;
* *bool flag11;
* *bool flag12;
* *bool flag13;
};

But if I do that, i print out the sizeof(), that struct and it is 13.
So i think the compile use 1 byte for each flag.

Is it possible to create a struct so that each flag uses only 1 bit.

Yes, read about bitfields. *The syntax is the colon and the field width
after the name of the member, like

* * *bool flag1:1;

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

Thank you Victor.

I am going to follow you suggestion. If I create a class like this:
class myMask {
public:
bool flag1:1;
bool flag2:1;
bool flag3:1;
bool flag4:1;
bool flag5:1;
bool flag6:1;
bool flag7:1;
bool flag8:1;
bool flag9:1;
bool flag10:1;
bool flag11:1;
bool flag12:1;
bool flag13:1;
};

Can I set all the flag to 0 by doing this:

myMask mask;

memset(&mask, '\0', sizeof(myMask)) ;

And can I compare if 2 masks are the same by doing this:

myMask mask1;
myMask mask2;

memcmp(&mask1, &mask2, sizeof(myMask)) ;

Thanks.

[Hisense]

On 10ÔÂ30ÈÕ, ÏÂÎç1ʱ50·Ö, "Plisske...@gma il.com" <Plisske...@gma il.com>
wrote:

On Oct 29, 11:10 pm, Victor Bazarov <v.Abaza...@com Acast.netwrote:

Plisske...@gmai l.com wrote:

Is there an efficient way to create a struct of flag in C++?

I need to create a struct of boolean flag, like this:
struct testStruct {
bool flag1;
bool flag2;
bool flag3;
bool flag4;
bool flag5;
bool flag6;
bool flag7;
bool flag8;
bool flag9;
bool flag10;
bool flag11;
bool flag12;
bool flag13;
};

But if I do that, i print out the sizeof(), that struct and it is 13.
So i think the compile use 1 byte for each flag.

Is it possible to create a struct so that each flag uses only 1 bit.

Yes, read about bitfields. The syntax is the colon and the field width
after the name of the member, like

bool flag1:1;

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

Thank you Victor.

I am going to follow you suggestion. If I create a class like this:
class myMask {
public:
bool flag1:1;
bool flag2:1;
bool flag3:1;
bool flag4:1;
bool flag5:1;
bool flag6:1;
bool flag7:1;
bool flag8:1;
bool flag9:1;
bool flag10:1;
bool flag11:1;
bool flag12:1;
bool flag13:1;
};

Can I set all the flag to 0 by doing this:

myMask mask;

memset(&mask, '\0', sizeof(myMask)) ;

And can I compare if 2 masks are the same by doing this:

myMask mask1;
myMask mask2;

memcmp(&mask1, &mask2, sizeof(myMask)) ;

Thanks.- Òþ²Ø±»ÒýÓÃÎÄ×Ö -

- ÏÔʾÒýÓõÄÎÄ×Ö -

there are two things to say:
1, you need no class, but struct, because struct is good enough to
solve it;
2, either class or struct, you could use ctor where all the bit fields
are set to 0 or any value you want.

[anon]

Hisense wrote:

>>
I am going to follow you suggestion. If I create a class like this:
class myMask {
public:
bool flag1:1;
bool flag2:1;
bool flag3:1;
bool flag4:1;
bool flag5:1;
bool flag6:1;
bool flag7:1;
bool flag8:1;
bool flag9:1;
bool flag10:1;
bool flag11:1;
bool flag12:1;
bool flag13:1;
};

Can I set all the flag to 0 by doing this:

myMask mask;

memset(&mask, '\0', sizeof(myMask)) ;

Proper way is:

myMask mask = myMask();

>And can I compare if 2 masks are the same by doing this:

myMask mask1;
myMask mask2;

memcmp(&mask 1, &mask2, sizeof(myMask)) ;

No, because of padding, some bits can be left uninitialized, therefore
you have to compare each field.
I am not sure if you can do this (probably not)
if(mask1 == mask2)
{
....
}

2, either class or struct, you could use ctor where all the bit fields
are set to 0 or any value you want.

POD structures can not have constructors. Read here:
http://www.fnal.gov/docs/working-gro...x/doc/POD.html

[James Kanze]

On Oct 30, 6:50 am, "Plisske...@gma il.com" <Plisske...@gma il.com>
wrote:

On Oct 29, 11:10 pm, Victor Bazarov <v.Abaza...@com Acast.netwrote:

Plisske...@gmai l.com wrote:

Is there an efficient way to create a struct of flag in C++?

I need to create a struct of boolean flag, like this:
struct testStruct {
bool flag1;
bool flag2;
bool flag3;
bool flag4;
bool flag5;
bool flag6;
bool flag7;
bool flag8;
bool flag9;
bool flag10;
bool flag11;
bool flag12;
bool flag13;
};

But if I do that, i print out the sizeof(), that struct and it is 13.
So i think the compile use 1 byte for each flag.

Is it possible to create a struct so that each flag uses only 1 bit.

Yes, read about bitfields. The syntax is the colon and the field width
after the name of the member, like

bool flag1:1;

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

Thank you Victor.

I am going to follow you suggestion. If I create a class like this:
class myMask {
public:
bool flag1:1;
bool flag2:1;
bool flag3:1;
bool flag4:1;
bool flag5:1;
bool flag6:1;
bool flag7:1;
bool flag8:1;
bool flag9:1;
bool flag10:1;
bool flag11:1;
bool flag12:1;
bool flag13:1;
};

Can I set all the flag to 0 by doing this:

myMask mask;

memset(&mask, '\0', sizeof(myMask)) ;

And can I compare if 2 masks are the same by doing this:

myMask mask1;
myMask mask2;

memcmp(&mask1, &mask2, sizeof(myMask)) ;

Thanks.

[Victor Bazarov]

Pl********@gmai l.com wrote:

[..] If I create a class like this:
class myMask {
public:
bool flag1:1;
bool flag2:1;
bool flag3:1;
bool flag4:1;
bool flag5:1;
bool flag6:1;
bool flag7:1;
bool flag8:1;
bool flag9:1;
bool flag10:1;
bool flag11:1;
bool flag12:1;
bool flag13:1;
};

Can I set all the flag to 0 by doing this:

myMask mask;

That will leave them undefined. Consider defining the default
constructor and the comparison operator.

>
memset(&mask, '\0', sizeof(myMask)) ;

And can I compare if 2 masks are the same by doing this:

myMask mask1;
myMask mask2;

memcmp(&mask1, &mask2, sizeof(myMask)) ;

It is better to have the overloaded operator== in your class.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[Plissken.s]

On Oct 30, 9:22*am, Victor Bazarov <v.Abaza...@com Acast.netwrote:

Plisske...@gmai l.com wrote:

[..] *If I create a class like this:
class myMask {
public:
* * *bool flag1:1;
* * *bool flag2:1;
* * *bool flag3:1;
* * *bool flag4:1;
* * *bool flag5:1;
* * *bool flag6:1;
* * *bool flag7:1;
* * *bool flag8:1;
* * *bool flag9:1;
* * *bool flag10:1;
* * *bool flag11:1;
* * *bool flag12:1;
* * *bool flag13:1;
* };

Can I set all the flag to 0 by doing this:

* * myMask mask;

That will leave them undefined. *Consider defining the default
constructor and the comparison operator.

* * memset(&mask, '\0', sizeof(myMask)) ;

And can I compare if 2 masks are the same by doing this:

myMask mask1;
myMask mask2;

memcmp(&mask1, &mask2, sizeof(myMask)) ;

It is better to have the overloaded operator== in your class.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

Thank you for all the help.

In my case, I have this class which only have
~200 boolean flags. I am thinking if there is a faster way to
* initialize all of them to false
* compare if 2 classes have the same values (the same set of flags are
set)

Thank you again.

[.rhavin grobert]

On 30 Okt., 06:50, "Plisske...@gma il.com" <Plisske...@gma il.com>
wrote:

On Oct 29, 11:10*pm, Victor Bazarov <v.Abaza...@com Acast.netwrote:

Plisske...@gmai l.com wrote:

Is there an efficient way to create a struct of flag in C++?

I need to create a struct of boolean flag, like this:
struct testStruct {
* *bool flag1;
* *bool flag2;
* *bool flag3;
* *bool flag4;
* *bool flag5;
* *bool flag6;
* *bool flag7;
* *bool flag8;
* *bool flag9;
* *bool flag10;
* *bool flag11;
* *bool flag12;
* *bool flag13;
};

But if I do that, i print out the sizeof(), that struct and it is 13.
So i think the compile use 1 byte for each flag.

Is it possible to create a struct so that each flag uses only 1 bit.

Yes, read about bitfields. *The syntax is the colon and the field width
after the name of the member, like

* * *bool flag1:1;

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

Thank you Victor.

I am going to follow you suggestion. If I create a class like this:
class myMask {
public:
* * *bool flag1:1;
* * *bool flag2:1;
* * *bool flag3:1;
* * *bool flag4:1;
* * *bool flag5:1;
* * *bool flag6:1;
* * *bool flag7:1;
* * *bool flag8:1;
* * *bool flag9:1;
* * *bool flag10:1;
* * *bool flag11:1;
* * *bool flag12:1;
* * *bool flag13:1;
* };

Can I set all the flag to 0 by doing this:

* * myMask mask;

* * memset(&mask, '\0', sizeof(myMask)) ;

And can I compare if 2 masks are the same by doing this:

myMask mask1;
myMask mask2;

memcmp(&mask1, &mask2, sizeof(myMask)) ;

try this:

struct myMask {
union {
unsigned int nMask;
struct {
bool flag1:1;
bool flag2:1;
bool flag3:1;
bool flag4:1;
bool flag5:1;
bool flag6:1;
bool flag7:1;
bool flag8:1;
bool flag9:1;
bool flag10:1;
bool flag11:1;
bool flag12:1;
bool flag13:1;
};
};
};

inline bool operator==(myMa sk const& rm, myMask const& lm)
{return rm.nMask == lm.nMask;};

the union will force your compiler to put all the bits into one int.
you can the set the int to 0 to clear all bits and compare the ints to
compare the masks.

Just a hint: you'll never need '/0'. just write 0. '/0' is just used
to inform the readers of your code: "hey folks, this is explicitely
meant as a char in a string". so if you want to do something weired:

int i = 20;
while (i-->'\0')
{
if (i == '/2')
{
CallSomeMessage Func("I've reached 2!");
}
}

[.rhavin grobert]

On 30 Okt., 16:03, ".rhavin grobert" <[e-mail] wrote:

On 30 Okt., 06:50, "Plisske...@gma il.com" <Plisske...@gma il.com>
wrote:

On Oct 29, 11:10*pm, Victor Bazarov <v.Abaza...@com Acast.netwrote:

Plisske...@gmai l.com wrote:
Is there an efficient way to create a struct of flag in C++?

I need to create a struct of boolean flag, like this:
struct testStruct {
* *bool flag1;
* *bool flag2;
* *bool flag3;
* *bool flag4;
* *bool flag5;
* *bool flag6;
* *bool flag7;
* *bool flag8;
* *bool flag9;
* *bool flag10;
* *bool flag11;
* *bool flag12;
* *bool flag13;
};

But if I do that, i print out the sizeof(), that struct and it is 13.
So i think the compile use 1 byte for each flag.

Is it possible to create a struct so that each flag uses only 1 bit..

Yes, read about bitfields. *The syntax is the colon and the field width
after the name of the member, like

* * *bool flag1:1;

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

Thank you Victor.

I am going to follow you suggestion. If I create a class like this:
class myMask {
public:
* * *bool flag1:1;
* * *bool flag2:1;
* * *bool flag3:1;
* * *bool flag4:1;
* * *bool flag5:1;
* * *bool flag6:1;
* * *bool flag7:1;
* * *bool flag8:1;
* * *bool flag9:1;
* * *bool flag10:1;
* * *bool flag11:1;
* * *bool flag12:1;
* * *bool flag13:1;
* };

Can I set all the flag to 0 by doing this:

* * myMask mask;

* * memset(&mask, '\0', sizeof(myMask)) ;

And can I compare if 2 masks are the same by doing this:

myMask mask1;
myMask mask2;

memcmp(&mask1, &mask2, sizeof(myMask)) ;

try this:

struct myMask {
* union {
* * unsigned int nMask;
* * struct {
* * * bool flag1:1;
* * * bool flag2:1;
* * * bool flag3:1;
* * * bool flag4:1;
* * * bool flag5:1;
* * * bool flag6:1;
* * * bool flag7:1;
* * * bool flag8:1;
* * * bool flag9:1;
* * * bool flag10:1;
* * * bool flag11:1;
* * * bool flag12:1;
* * * bool flag13:1;
* *};
* };

};

inline bool operator==(myMa sk const& rm, myMask const& lm)
{return rm.nMask == lm.nMask;};

the union will force your compiler to put all the bits into one int.
you can the set the int to 0 to clear all bits and compare the ints to
compare the masks.

Just a hint: you'll never need '/0'. just write 0. '/0' is just used
to inform the readers of your code: "hey folks, this is explicitely
meant as a char in a string". so if you want to do something weired:

int i = 20;
while (i-->'\0')
{
* if (i == '/2')
* {
* * CallSomeMessage Func("I've reached 2!");
* }

}

typo: " if (i == '/2') " should be " if (i == '\2') "