Question

I am working on C firmware project. I have a union that is defined as,

typedef union {
    unsigned long value;
    unsigned char bytes[4];
} LONGVALUE;

I also have a function that has this prototype,

char sendHexToASCII_UART(char *msg, int cnt);

and a variable of type LONGVALUE defined as,

LONGVALUE countAddr;

THE PROBLEM:
I fill the individual bytes of the union variable with values from an array (tempBuff1), I then want to pass the address of the first element in the union to a function that will print it to the UART. On my function call sendHexToASCII_UART((int *)countAddr.bytes[0], 4);, I get a compiler warning saying “cast to pointer from integer of different size”. Can someone explain why I am getting this and how I can make it go away? NOTE: Changing the (int *) cast to (char *) causes the same warning.

countAddr.bytes[0] = tempBuff1[COUNT_ADDR - PWRD_ADDRESS];
countAddr.bytes[1] = tempBuff1[COUNT_ADDR - PWRD_ADDRESS + 1];
countAddr.bytes[2] = tempBuff1[COUNT_ADDR - PWRD_ADDRESS + 2];
countAddr.bytes[3] = tempBuff1[COUNT_ADDR - PWRD_ADDRESS + 3];
sendHexToASCII_UART((int *)countAddr.bytes[0], 4); 

Answer 1

Why not just:

sendHexToASCII_UART((char *)countAddr.bytes, 4);

or even better:

sendHexToASCII_UART((char *)countAddr.bytes, sizeof(countAddr.bytes));