Don't care if you call me stupid..

Don't care if you call me stupid..

Kevin Epps

Member #5,856

May 2005

I just CANNOT think of how to do this for some reason. And since I don't really know the term for it, It's hard to search for what I'm looking for.

Does ANYONE know what it's called to pass several values in one argument of a function in c++?

Example:

void func(arg1, val1 | val2 | val3, arg3);

I think you're supposed to make the argument in question a type of unsigned. If that's so how do extract each value from that one argument?

Steve Terry

Member #1,989

March 2002

That's a binary OR operation.

1enum { val1 = 1, val2 = 2, val3 = 4 }val;
2 
3void func(val v)
4{
5    if(v & val1)
6    {
7 
8    }
9    if(v & val2)
10    {
11 
12    }
13}
14 
15int main(int argc, char **argv)
16{
17   func(val1 | val2);
18}

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Kevin Epps

Member #5,856

May 2005

AHHH! ENUMERATION!!!

Thanks so much, Steve!

Thomas Fjellstrom

Member #476

June 2000

You dont even need the enum.

#define foo  1
#define bar  2
#define baz  4
#define frob 8

// or

const int foo  = 1;
const int bar  = 2;
const int baz  = 4;
const int frob = 8;

Notice the pattern. You can also use shifts to make the values, if you think it helps understanding..

const int foo  = 1; // << 0
const int bar  = 1     << 1;
const int baz  = 1     << 2;
const int frob = 1     << 3;

Basically "flags" need to have one bit in the integer set to on, and the rest off for this to work properly. Powers of two just happen to have this property.

--
Thomas Fjellstrom - [website] - [email] - [Allegro Wiki] - [Allegro TODO]
"If you can't think of a better solution, don't try to make a better solution." -- weapon_S
"The less evidence we have for what we believe is certain, the more violently we defend beliefs against those who don't agree" -- https://twitter.com/neiltyson/status/592870205409353730

Kevin Epps

Member #5,856

May 2005

Hey Thomas,

That really didn't help me much. I don't have a problem understanding that part, it's how to declare the function that's going to use the flags.

What I'm trying to do is make a function that's passed several flags that then write out a message based on the flags passed.

I tried Steve's approach, but I get an error message saying that I can't convert a const int to an enum.

Then I tried Thomas's approach somewhat, but I don't know if I'm declaring the function correctly.

1#define    KEV    1
2#define    A_H    2
3#define    A_F    3
4#define    JER    4
5#define    STE    5
6#define    MIK    6
7#define    NAU    7
8#define    DAN    8
9#define    IV    9
10#define    ROB    10
11 
12/*enum NAMES { KEV, A_H, A_F, JER, STE, MIK, NAU, DAN, IV, ROB };*/
13 
14#define    KEVIN_E    "Kevin Epps"
15#define    ADAM_H    "Adam Howard"
16#define    ADAM_F    "Adam Friday"
17#define    JEREMY_L  "Jeremy Landig"
18#define    STEVEN_C  "Steven Cooper"
19#define    MIKE_P    "Mike Phillips"
20#define    NAUMAN_H  "Nauman Hafiz"
21#define    DANNY_L    "Danny Luisi"
22#define    IVAN_D    "Ivan Dixon"
23#define    ROBERT_P  "Robert Parks"
24 
25void show_credits(BITMAP *buffer, char *category, const int nam, int y, int num_of_names)
26{
27  int new_y = y+text_height(money_fonts) + 5;
28  textprintf_centre_ex(buffer, money_fonts_2, 320, y, -1, -1, category);
29  if(nam == KEV)
30  {
31    textprintf_centre_ex(buffer, dialog_fonts, 320, new_y, -1, -1, "%s", KEVIN_E);
32    new_y+=text_height(dialog_fonts);
33  }
34  if(nam == A_H)
35  {
36    textprintf_centre_ex(buffer, dialog_fonts, 320, new_y, -1, -1, "%s", ADAM_H);
37    new_y+=text_height(dialog_fonts);
38  }
39  if(nam == A_F)
40  {
41    textprintf_centre_ex(buffer, dialog_fonts, 320, new_y, -1, -1, "%s", ADAM_F);
42    new_y+=text_height(dialog_fonts);
43  }
44}

And I called the function like this:

show_credits(fade_buffer, "Project Manager", KEV | A_F, 300, 2);
/*Is supposed to print out:
Project Manager
Kevin Epps
Adam Friday*/

But "Adam Friday"'s the only text shown under Project Manager.

(Also, if I change the conditionals back to (nam & whatever), then the all print regardless of the flags passed thru.

Carrus85

Member #2,633

August 2002

Well, there are two problems with that code:
One, your enumeration values (or defines, in this case), need to be powers of two, not counting numbers.
Two, testing for equality directly is not going to work, you need to and the mask (code, in other words) with your nam variable:

1#define    KEV    1
2#define    A_H    2
3#define    A_F    4
4#define    JER    8
5#define    STE    16
6#define    MIK    32
7#define    NAU    64
8#define    DAN    128
9#define    IV    256
10#define    ROB    512
11 
12/*enum NAMES { KEV, A_H, A_F, JER, STE, MIK, NAU, DAN, IV, ROB };*/
13 
14#define    KEVIN_E    "Kevin Epps"
15#define    ADAM_H    "Adam Howard"
16#define    ADAM_F    "Adam Friday"
17#define    JEREMY_L  "Jeremy Landig"
18#define    STEVEN_C  "Steven Cooper"
19#define    MIKE_P    "Mike Phillips"
20#define    NAUMAN_H  "Nauman Hafiz"
21#define    DANNY_L    "Danny Luisi"
22#define    IVAN_D    "Ivan Dixon"
23#define    ROBERT_P  "Robert Parks"
24 
25void show_credits(BITMAP *buffer, char *category, const int nam, int y, int num_of_names)
26{
27  int new_y = y+text_height(money_fonts) + 5;
28  textprintf_centre_ex(buffer, money_fonts_2, 320, y, -1, -1, category);
29  if(nam & KEV)
30  {
31    textprintf_centre_ex(buffer, dialog_fonts, 320, new_y, -1, -1, "%s", KEVIN_E);
32    new_y+=text_height(dialog_fonts);
33  }
34  if(nam & A_H)
35  {
36    textprintf_centre_ex(buffer, dialog_fonts, 320, new_y, -1, -1, "%s", ADAM_H);
37    new_y+=text_height(dialog_fonts);
38  }
39  if(nam & A_F)
40  {
41    textprintf_centre_ex(buffer, dialog_fonts, 320, new_y, -1, -1, "%s", ADAM_F);
42    new_y+=text_height(dialog_fonts);
43  }
44}

Edit:

Ah, just noticed the last line of your post. Yes, the &'s are required. They just don't work if you don't set the nam value correctly! The codes must be powers of two in order to be set in the bitmask properly. Oh, and just as a note, it might be wise to make your function take a const unsigned int nam instead of a const int, to avoid any potential weirdness with the signs.

Kevin Epps

Member #5,856

May 2005

THERE we go!! It works now! I was missing the point about the powers of two bit. Thanks man.

Bob

Free Market Evangelist

September 2000

It sounds like you actually want a list of things in general, not just list of bits. What's wrong with passing an array (or vector) of string?

--
- Bob
[ -- All my signature links are 404 -- ]

Kris Asick

Member #1,424

July 2001

Think of it this way, Kevin:

Computers work on bits, 1's and 0's, thus each number is a combination of bits. For instance:

33 = 00100001, 145 = 10010001, 26710 = 0110100001010110

What you're doing is a form of "bitmasking" usually called "flags" or "tags". The idea is that one variable stores multiple true/false values in each bit. The reason why you need to use powers of 2 is because each power of 2 only touches one bit:

So let's give these all values:

#define FLAG_SOLID  1
#define FLAG_PHASED  2
#define FLAG_IMMUNE  4
#define FLAG_SPHERICAL  8
#define FLAG_AI    16
#define FLAG_AUTOMOVE  32
#define FLAG_SPECIAL  64
#define FLAG_PLAYER  128

Now, you simply use a bit-wise OR operation, the | symbol, to combine them, which effectively does something like this:

0100101110100101 | 1010100101110100 = 1110101111110101

Thus if you did this:

variable = FLAG_PHASED | FLAG_AI | FLAG_SPECIAL

...the result is:

00000010 | 00010000 | 01000000 = 01010010

Then when you want to check if a particular flag is set or not, you use a bit-wise AND operation instead, which is the & symbol:

if (variable & FLAG_AI) ProcessAI();

if (variable & FLAG_SPECIAL) TriggerSpecial();

Make sense now?

You'll also note that using '+' instead of '|' works the exact same under these circumstances, provided you don't accidentally add the same flag more than once. (But you can't use '-' in place of '&'!)

--- Kris Asick (Gemini)
--- http://www.pixelships.com

Kevin Epps

Member #5,856

May 2005

thanks for the input. I got working after Carrus's explanation and I understand it now. I had just forgotten about setting up the flags to be powers of two. Thanks guys for you help.

Johan Halmén

Member #1,550

September 2001

Stupid! Couldn't resist. Actually you're not. That was a good question. And remember, there are no stupid questions, just a lot of inquisitive idiots... Sorry again.

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Fladimir da Gorf

Member #1,565

October 2001

class Clazz {
   Clazz operator | (const Clazz &other) {
      return //..
   }
};

const Clazz OPT1( ... );
const Clazz OPT2( ... );
const Clazz OPT3( ... );

callFunc( OPT1 | OPT2 | OPT3 );

Tee hee

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KnightWhoSaysNi

Member #7,339

June 2006

Thank you for asking this question. It has helped me too. Before reading this I had a few functions that were something like this:

void drawtext(srting text, int size, bool bold, bool italic, bool underline, bool strikeout, bool etc...)