| operator

[meresaath]

Hello

I'm creating my edit box in my OnInitdialog() like this. this works fine.

CRect rect(100,100, 200, 130); // L,T,R,B
CEdit* pEdit = new CEdit;
DWORD dwstyles;
dwstyles = WS_BORDER|WS_CHILD|WS_VISIBLE|ES_AUTOHSCROLL;
pEdit->Create(dwstyles, rect, this, IDC_EDIT1);

Now I want to make my edit box ES_NUMBER, but I don't want to just add it to my dwstyles, I want to learn how to do the or(|) thing. Can anyone explain me how to go about it.

thanks

[peterchen]

The '|' operator does an bitwise 'or'. In long terms c=a|b means:
- look at a and b in binary
- for each bit position: if the bit is set in a, or b, or both, set the bit in c, otherwise, clear it:
a=0011
b=1010
------
c=1011

Now for the window styles: they typically have only one bit set. so ES_FOO might be 0010 binary. The effect of '|' instead of '+' is: if the bit is already set, nothing bad happens. e.g. we have a=0011, (the ES_FOO bit is already set). if we now add them:
0011
+0010
----
0101
So other bits are affected, and the bit we wanted to set is actually re-set. Sing or:

0011
|0010
----
0011
everything is fine.

Peter

[meresaath]

sorry, but I have no clue what you just said. Now for starter how do I find out the binary value of ES_FOO, and how do I know what is the ES_FOO(with the bit set).

thanks

[peterchen]

Hi,

Well.. if you didn't hear of binary numbers before, perhaps this information is enough: If you add the ES_NUMBER style using '+', the result is wrong if the style was already set. Using '|', it works well even if ES_NUMBER is already set.

There are other cases where binary operations are far more important, here it's just 'good style'.

To understand hexadecimal & binary representation of numbers, you might want to grab a neat "math for dummies" book. It#s tough to make you UNDERSTAND in a few lines.

Peter

[O-Deka-K]

You don't actually need to know the binary values. All you need to know is how to use the bitwise-OR (|) and bitwise-AND (&) operations. Peter was just trying to explain why this works.

To add a style:

dwStyle |= ES_NUMBER;
// OR
dwStyle = dwStyle | ES_NUMBER;



To subtract a style:

dwStyle &= ~ES_NUMBER;
// OR
dwStyle = dwStyle & ~ES_NUMBER;



BTW, "set" means 1, and "clear" means 0. "[Window styles] typically have only one bit set" means that they are binary numbers that have a single 1, with the rest as zeroes (e.g. 0010). He wasn't talking about a "set of bits".

O-Deka-K

[meresaath]

thanks, this is what I was looking for.