printf int in binary format

william007
william007 used Ask the Experts™
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How to printf integer, byte etc in their binary format?
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ozo
Most Valuable Expert 2014
Top Expert 2015

Commented:
what do you mean when you say "in their binary format"?
ozo
Most Valuable Expert 2014
Top Expert 2015

Commented:
are you asking about %x

Author

Commented:
Hi, let say int i=4;
%x will be printing as hex form 4
But what I want is the binary form which is the 0100.
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ozo
Most Valuable Expert 2014
Top Expert 2015

Commented:
there is no standard printf format to do that.
you could write a function to do that.
How are you deciding how many leading 0s are in the binary form?

Author

Commented:
Hi ozo,
For the leading 0s I will consider omitted it.
But if we must write a function, then I would suggest to make it as a flag in the argument.
ozo
Most Valuable Expert 2014
Top Expert 2015

Commented:
how should the flag be interpreted?
This is a function I wrote sometime back, can be used to print in any base(between 2 and 36).
for base >36, we need more symbols than just numbers and alphabets.
maxwidth is the size of the dest buffer.

char * toString(int num, char * dest, unsigned radix, unsigned  maxwidth)
{
        if(!dest)
                return dest;
        if (radix < 2 || radix > 36)
        {
                dest[0] = 0;
                return dest;
        }

        int out = num;
        unsigned len = 0, i =0;
        int rem;

        while(out&& len<maxwidth)
        {
                rem = out % radix;
                out =  out/radix;
                if (rem > 9)
                        dest[len] = (char)(rem - 10) + 'a';
                else
                        dest[len] = (char)rem + '0';

                ++len;
        }

        if(!len)
                dest[len++]='0';//for number 0

        dest[len] = 0;

        // reverse digits
        for (i = 0; i < (len >> 1); ++i)
        {
                char c = dest[i];
                dest[i] = dest[len-1-i];
                dest[len-1-i] = c;
        }
}

Author

Commented:
>how should the flag be interpreted?
Something like convertToBinary(char omitZeroflag...
and check the omitZeroflag to decide whether we want to omit zero...
Since this is just a on and off switch..in Java we can use boolean, but I don't really confirm that what is the best way to implement in C(Can someone tell me what is the best way to do a on and off switch in C?).  Anyway, I think I have got many good idea to get the binary here, thanks for the question:)

>>How are you deciding how many leading 0s are in the binary form?
You did not mention the number of zeros you want. (there is no straight answer to this, it is best not to display any leading zeros or always display fixed width numbers; say 32 or 64 digits)

BTW, the function I posted works for unsigned numbers, negative numbers will get printed in 2's compliment format.

There is a miss-by-one error in the while loop condition,
it should be
while(out && len<maxwidth-1)

>Can someone tell me what is the best way to do a on and off switch in C?
usually an int is used(0 = false, anything else = true)

if you include stdbool.h, then you can use the bool datatype in C.

however, for most systems bool is not guaranteed to be 1 byte (can be as large as 8 bytes on some old systems),
till sometime back, the only thing you could assume was that size of bool <= size of long.
Though on latest versions on gcc, it is 1 byte.

Author

Commented:
>usually an int is used(0 = false, anything else = true)
Hi, I am curious why don't we use char...since int is 2 bytes(short integer, generally) but char is 1 byte, which can save more spaces?
if memory is an issue, char should be used. if it is a big issue and a lot of bools are needed, use each bit of an int as a bitmap.
if there are only a few bool on modern systems with memory running into GBs, it will not even me measurable, so does not matter at all.

however, i think the idea of using int where bool could be because:
-IMHO int as greater readability than char when used as bool (char 0 is non printable, while int 0 is)
-int used to be the default(implicit) datatype for lot of cases in C(not sure about this though)
Top Expert 2006
Commented:
Typically chars indeed are used for bool. 1 (non zero or !0) being true and 0 being false. chars are internally stored as ints. To print 0 and 1, use %d flag instead of %c - this would print the ASCII value of the char.

Author

Commented:
Thanks=)

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