How to define a QBitArray variable in a struct?

[mohmo]

I define a struc like below and then i make an array of this structure:

struct mm{QBitArray bb; int val;};
mm* vec=new mm [10];

then i want to set a bit:
u [7].bb.setBit(3,1);

I encounter a crash message.
whats wrong with this definition?

[Chris Kawa]

Is u the same as vec ?
Do you set the size of the bit array somewhere? If not then accessing bit 3 of array of size 0 will obviously be undefined behavior (crash in your case).

[mohmo]

yeah sorry:
vec [7].bb.setBit(3,1);
but i cant set the length in the struct!:
struct mm{QBitArray bb(8); int val;};
this causes error.
How do you define a bitarray in a structure?

[Chris Kawa]

With that syntax you're trying to call a function(a constructor). You can't call a function at a declaration. It's a compile-time construct.

You have several choices:
@
//if your compiler supports c++11 use uniform initialization:
struct mm{
QBitArray bb{8};
int val;
};

//if it doesn't you can either define a constructor:
struct mm{
mm() : bb(8) {}
QBitArray bb;
int val;
};

//or just resize the thing later on:
struct mm{
QBitArray bb;
int val;
};
//somewhere later:
mm foo;
foo.bb.resize(8);
@

[mohmo]

Thanks chris
if we choose your third approach, HOW can i define the structure mm on HEAP and in the form of an ARRAY??
like:
mm* foo=new foo [10]; or something like that.

[Chris Kawa]

new mm, not new foo. Then you would resize each element in a for loop:
@
mm* foo = new mm[10];
for(int i=0; i< 10; ++i)
foo[i].bb.resize(8);
@
But I would favor the first option. the loop is then unnecessary.