unsigned long to char

[MaxD]

how to change unsigned long to char?

CODE: SELECT_ALL_CODE

unsigned long currentData = 12345678;
char res[4];

res[0] = currentData & 0x000000FF;
res[1] = (currentData & 0x0000FF00) >>8;
res[2] = (currentData & 0x00FF0000) >>16;
res[3] = (currentData & 0xFF000000) >>24;


what I expect:
res[0] = 78
res[1] = 65
res[2] = 34
res[3] = 12

But I can't get the correct value. Why?

[ABSF]

For those who are interested in knowing what the problems could be, read here...

http://forum.allaboutcircuits.com/showt ... hp?t=70479

Allen

[robosang]

Din went to the link Allen paste, but first guess would be the decimal value and hexadecimal value.

You assign the value with decimal value, but when you shift, the controller is shifting in binary bits So definitely you cannot get what you expect.

The formula works, just your assignment is in decimal, you should assign it in hexadecimal, it should works

[yonghui]

unsigned long currentData = 12345678;
char res[4];

res[0] = currentData & 0x000000FF;
res[1] = (currentData & 0x0000FF00) >>8;
res[2] = (currentData & 0x00FF0000) >>16;
res[3] = (currentData & 0xFF000000) >>24;

u do it in binary and u will know why.
convert decimal 12345678 to binary. then do it.


regards,
yh

[MaxD]

OK, I know the problem. But what if, in my actual case, the long type value is read from the PORTS of the PIC. So I want to extract the value into the char array because I send/receive the data is in char array format (byte by byte).

[takao21203]

there is more than one way.

All you need is practice with C.

You can for instance use typecast:

(char) (currentData >> 16) & 0xff

or you can use a pointer to the long data, and use this for char array as well.
This is however "dirty", if you port it, you get endian issues. For most programs it's not too much relavent = means don't care.

if you don't get correct value for the typecase you must use 0x000000ff, or 0x00ff0000.

[takao21203]

the original code can't work as pointed out, you should use 0x12345678 but that also is not decimal.