Thread: Array inside an 2dimensional array

First of all I would like to apologize if my question has been answered in the past...


I want to create a 30 columns *2 rows array (A[30][2]) and store at every element of it another array.

Practically, I want to store 8 bit binary addresses in a 2dimensional array, however I want these addresses to be stored as arrays and not as integers as I want to be able to read them byte by byte.

Therefore

Code:

int A[30][2];

as declaration is not what I want.

What I want is to store

Code:

B[8]={0,0,0,0,1,1,1,1}, C[8]=..., etc at every element of A[30][2].

If somebody could help me I would be grateful!!!

Thank you very much in advance.

Maybe a 3 dimensional array? Or have I just missed your point?

Originally Posted by mike_g

Maybe a 3 dimensional array? Or have I just missed your point?

Yes, you 're right, I didn' t explain well what I want...

If I declare an

Code:

int A[30][2][8];

array I will have to fill it up like this:

Code:

A[0][0][0] = 0;
A[0][0][1] = 0;
A[0][0][2] = 0;
A[0][0][3] = 0;
A[0][0][4] = 1;
A[0][0][5] = 1;
A[0][0][6] = 1;
A[0][0][7] = 1;

which represents the first byte 11110000 (from MSB to LSB).

I will have to repeat this 30*2 = 60 times.

Could you please tell how I could put in every element of the 30*2 array directly a full byte as an array?
How can I just declare

Code:

B[8] = {0,0,0,0,1,1,1,1};

and then just put it inside A[0][0]?

Thank you again for your time...

Use a union and a struct with bitfields:

Code:

union
{
    unsigned char thebyte;
    struct
    {
        unsigned int bit1:1;
        unsigned int bit2:1;
        unsigned int bit3:1;
        unsigned int bit4:1;
        unsigned int bit5:1;
        unsigned int bit6:1;
        unsigned int bit7:1;
        unsigned int bit8:1;
    }bits;
}byte;

int main(void)
{
    byte.thebyte = 0;

    byte.bits.bit8 = 1;  // equivalent to 1000 0000 (msb to lsb order)


    printf("Byte is: %d\n", byte.thebyte);

    return 0;
}

Originally Posted by Dave_Sinkula

Code:

unsigned char array[2][30];
array[0][0] = 0xF0;

?

This would be just fine if I just wanted to be able to write a full 8 bit binary at once and read it at once. However, I mentioned that I' ll have to be able to read the data bit by bit as I will send them through a serial port to a external hardware device bit by bit . So it is very helpful for me that each bit is an array element.

p.s. I' m sorry for the "stupid" questions, however I' m much more familiar with hardware programming than with software programming.

Originally Posted by mike_g

Maybe you could use bitwise operators to filter out the bits in the byte you want?

Untested, but maybe something like:

Code:

int GetBit(unsigned char byte, unsigned char bit)
{
    bit = 1 << bit;
    return (byte & bit);
}

int main()
{
    unsigned char byte = 0xFF;
    int state = GetBit(byte, 4);
}

This seems practical. I will try it and give you the feedback in a while.

Thank you for your time and patience...

Originally Posted by Dave_Sinkula

This serial port doesn't use a byte-sized shift register like every other CPU under the sun?

I wish it did... it would have made my work much easier.

It' s a Nios II Stratix II board (for those who know) of which I can control the I/O pins. Therefore I have to create a program that will work as hardware does.
Specifically, I use the one pin as a clock (practically by constantly changing its output from 0 to 1) and in the same time I use the other pin to send bit by bit the data synchronized with the clock. That' s why I can' t send the whole byte at once, as I'm not using an existing hardware.

@Dave_Sinkula

I used this:

Code:

#include "stdafx.h"
#include <stdio.h>
#include <windows.h>
#include "math.h"


int GetBit(unsigned char byte, unsigned char bit)
{
    bit = 1 << bit;
    return (byte & bit);
}

int _tmain(int argc, _TCHAR* argv[])
{
	unsigned char byte = 0x2B;
    int i;
	
	for (i=7;i>-1;i--)
	{
		int state = GetBit(byte, i);
        
		if (state == 0)
		{
			printf("%d",state);
		}
		else
		{
			state = state/(pow(2,i));
			printf("%d",state);
		}
	}

	for(;;)
	{
	}
}

to test it and it' s just what I wanted! Now I can use a 2 dimension array with unsigned char elements.
I just had to add

Code:

state = state/(pow(2,i));

because without this state had as a value the power of 2 of the location of the bit.

You have been really helpful

If you want the get bit function to return 0 or 1 you could use:

Code:

int GetBit(unsigned char byte, unsigned char bit)
{
    bit = 1 << bit;
    if(byte & bit) return 1;
    return 0;
}

It would save using an expensive pow function

Originally Posted by mike_g

If you want the get bit function to return 0 or 1 you could use:

Code:

int GetBit(unsigned char byte, unsigned char bit)
{
    bit = 1 << bit;
    if(byte & bit) return 1;
    return 0;
}

It would save using an expensive pow function

True!!!

I made the change and it works just fine!

Thank you all! You have been really helpful!!!