Re[3]: [Dev-C++] using char* as bitfield

[<ca...@kr...>]

hi Per,

I'll show you my code now. somehow it does not work as planned..

char *alloc_bits(unsigned int);
void set_bit(char*, unsigned int);

int main(int argc, char *argv[])
{
    char *mybits;
    
    mybits = alloc_bits(60);

    if (mybits) printf("bits[%d]: %X\n",sizeof(mybits), *mybits);

    if (mybits) set_bit(mybits,2);

    if (mybits) printf("bits[%d]: %X\n",sizeof(mybits), *mybits);

    system("PAUSE");
    return 0;
}

char *alloc_bits(unsigned int bits)
{
    return calloc(((bits+7)/8), sizeof(char));
}

void set_bit(char* bits,unsigned int bit)
{
    bits[bit/8] |= 1 << (bit&3);
}

what exactly does the set_bit() function do?
I don't understand it fully especially the (bit&3) part.
also I am totally lost in writing a get_bit() function..

any help appreciated!

 
gruss
/Christian                   mailto:ca...@kr...

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I propose that the following character sequence for joke markers:

:-)

                             19-Sep-82 11:44    Scott E  Fahlman