Read one and multiple bytes in function

Hello

I need help in my embedded project. assume array is loaded with five bytes so we know the location of each byte and data stored in the location.

byte 1 = location for byte1 6422296 = 00
byte 2 = location for byte2 6422300 = 01

byte 3 = location for byte3 6422304 = 02
byte 4 = location for byte4 6422308 = 03
byte 5 = location for byte5 6422312 = 04


I need to design two function

*read one byte
*read five bytes

In the read one byte function, function would take the memory location of one byte and save result

in read multiple byte function, read five bytes by calling read one byte function

I made my attempt

Code:

---

#include<stdio.h>
// Function to read one byte
void ReadByte (int *N)
{
    //loop to read 8 bits
    for ( n = 0; n <8; n++ )   
    {
      /*read each bit of one byte */
    }
}
 
// Function to read five byte 
void ReadMultipleByte (int *P )
{
    //loop to read 5 bytes
    for ( n = 0; n <5; n++ )
    {
          // call the function to read one byte and it will run five time in loop
       
    }
}
void main ()
{
        int n;
    int Data[]= {0,1,2,3,4}; //five bytes are stored into array
       
        ReadMultipleByte (&Data)
    return 0;
}

---

Well you should change your data type from 'int' to 'unsigned char' to begin with.

Quote:

---

Originally Posted by Salem

Well you should change your data type from 'int' to 'unsigned char' to begin with.

---

I have done

Code:

---

#include<stdio.h>
// Function to read one byte
void ReadByte (unsigned char *N)
{
    //loop to read 8 bits
    for ( n = 0; n <8; n++ )   
    {
      /*read each bit of one byte */
    }
}
 
// Function to read five byte 
void ReadMultipleByte (unsigned char *P )
{
    //loop to read 5 bytes
    for ( n = 0; n <5; n++ )
    {
          // call the function to read one byte and it will run five time in loop
       
    }
}
void main ()
{
        int n;
    unsigned char Data[]= {0,1,2,3,4}; //five bytes are stored into array
       
        ReadMultipleByte (&Data[0])
    return 0;
}

---

Is my logic correct ?

Looks better.

Now just complete the code for the comments.

Quote:

---

Originally Posted by Salem

Looks better.

Now just complete the code for the comments.

---

My attempt

Code:

---

#include<stdio.h>

// Function to read one byte
void ReadByte (unsigned char *byteAddress)
{
    //loop to read 8 bits
    for ( n = 0; n <8; n++ )   
    {
                if ( condition1 )
            *byteAddress |= 1 ;
               
        if ( n < 7 )
            *byteAddress <<= 1 ; 
    }
       
}
 
// Function to read five byte 
void ReadMultipleByte ( unsigned char *byteAddress)
{
        int n;
        unsigned char R;
    //loop to read 5 bytes
    for ( n = 0; n <5; n++ ) 
    {
      R =  ReadByte( unsigned char *byteAddress)    // call the function to read one byte and it will run five time in loop
          ++byteAddress;
   
    }
}
void main ()
{
    int n;
    unsigned char Data[]= {0,1,2,3,4}; //five bytes are stored into array
   
    ReadMultipleByte ( Data])
    return 0;
}

---

Quote:

---

Originally Posted by Salem

Looks better.

---

I amtrying to fix some issues

why code doesn't print the correct value stored in the first memory location of array

Code:

---

#include<stdio.h>

int read (unsigned int N, unsigned int *p);


int read (unsigned int N, unsigned int *p)
{
        N = 5;
       
        for ( N = 5; N > 0; --N)
        {
                printf("\n read address %p \n value store at this address %d", (p + N), *( p + N));
        }
       
}


int main ()
{
        int s;
    int i = 5 ;
    int array[]= {20, 18, 21, 45, 42 };
       
    for (i = 5; i>0; --i)
        {
                printf ("%p  = %d \n", &array[i], array[i]);
        }               
 
        s= read (i, array);
       
  return 0;
}

---

0061FF28 = 3203072
0061FF24 = 42
0061FF20 = 45
0061FF1C = 21
0061FF18 = 18


read address 0061FF28
value store at this address 3203072
read address 0061FF24
value store at this address 42
read address 0061FF20
value store at this address 45
read address 0061FF1C
value store at this address 21
read address 0061FF18
value store at this address 18

Just stop for a moment and ask yourself: in an array of 5 elements, is array[5] valid?

following approach work for me

Code:

---

#include<stdio.h>   

int read (unsigned int N, unsigned int *p);
 
int read (unsigned int N, unsigned int *p)
{
    int i;
          for (int i = N-1; i >= 0; i--) { 
          printf("\n read address %p \n ", (p + N-1)); 
      printf("value store at this address is = %d \n", *( p + N-1));
      --p;           
    }   
}
 
   
int main()   
{   
    int s;  int N = 5 ;  // length of array   
   
    //Initialize array   
    int Data[] = {1, 2, 3, 4, 5};   
       
    printf("Original array: \n");   
    for (int i = 0; i < N; i++) { 
        printf("%p  = %d \n", &Data[i], Data[i] );         
    }     
       
    printf("\n");   
       
    printf("Array in reverse order: \n");   
    //Loop through the array in reverse order   
    for (int i = N-1; i >= 0; i--) { 
        printf("%p  = %d \n", &Data[i], Data[i] );         
    }
    s= read (N, Data);       
    return 0;   
}

---

Original array:
0061FF0C = 1
0061FF10 = 2
0061FF14 = 3
0061FF18 = 4
0061FF1C = 5


Array in reverse order:
0061FF1C = 5
0061FF18 = 4
0061FF14 = 3
0061FF10 = 2
0061FF0C = 1


read address 0061FF1C
value store at this address is = 5


read address 0061FF18
value store at this address is = 4


read address 0061FF14
value store at this address is = 3


read address 0061FF10
value store at this address is = 2


read address 0061FF0C
value store at this address is = 1

> int i;
> for (int i = N-1; i >= 0; i--)
There's no point having the first declaration of i.

> printf("\n read address %p \n ", (p + N-1));
Try
printf("\n read address %p \n ", (p + i));

And stop messing about with decrementing p with p--
Since p points to the start of the array (in main), you're decrementing to somewhere before the beginning of the array.

Regardless, it's an invalid pointer.
Question 6.17