union and bits

[chandra sekhar nunna]

Hello All,

typedef union
{
int m_4ByteData;
char m_8bitData[4];
}data;

data conv;
conv.m_4ByteData = 1000;

I am using above union i am getting all the individual 8 bits ( 8 * 4 =
32 bits for int ). How to get the int value ( m_4ByteData) using
m_8bitData[4].

Thanks in advance
Chandra-

[olaf]

Just access the structure

typedef union
{
int m_4ByteData;
char m_8bitData[4];
}data;

data conv;
conv.m_4ByteData = 1000;
printf("m_8bitData = %d %d %d %d\n",
conv.m_8bitData[0],
conv.m_8bitData[1],
conv.m_8bitData[2],
conv.m_8bitData[3]);

It has the same memmory attached to it

so &(conv.m_4ByteData) == &(conv.m_8bitData[0]) is always TRUE.

Greetings Olaf

chandra sekhar nunna <n.*************@sisl.co.in> wrote in message news:<3F*************@sisl.co.in>...

Hello All,

typedef union
{
int m_4ByteData;
char m_8bitData[4];
}data;

data conv;
conv.m_4ByteData = 1000;

I am using above union i am getting all the individual 8 bits ( 8 * 4 =
32 bits for int ). How to get the int value ( m_4ByteData) using
m_8bitData[4].

Thanks in advance
Chandra-

[chandra sekhar nunna]

Hi,

Any idea how round double values using the same concept.

Bye
Chandra-

olaf wrote:

Just access the structure

typedef union
{
int m_4ByteData;
char m_8bitData[4];
}data;

data conv;
conv.m_4ByteData = 1000;
printf("m_8bitData = %d %d %d %d\n",
conv.m_8bitData[0],
conv.m_8bitData[1],
conv.m_8bitData[2],
conv.m_8bitData[3]);

It has the same memmory attached to it

so &(conv.m_4ByteData) == &(conv.m_8bitData[0]) is always TRUE.

Greetings Olaf

chandra sekhar nunna <n.*************@sisl.co.in> wrote in message news:<3F*************@sisl.co.in>...

Hello All,

typedef union
{
int m_4ByteData;
char m_8bitData[4];
}data;

data conv;
conv.m_4ByteData = 1000;

I am using above union i am getting all the individual 8 bits ( 8 * 4 =
32 bits for int ). How to get the int value ( m_4ByteData) using
m_8bitData[4].

Thanks in advance
Chandra-

[Dan Pop]

In <3F*************@sisl.co.in> chandra sekhar nunna <n.*************@sisl.co.in> writes:

Hello All,

typedef union
{
int m_4ByteData;
char m_8bitData[4];
}data;

data conv;
conv.m_4ByteData = 1000;

I am using above union i am getting all the individual 8 bits ( 8 * 4 =
32 bits for int ). How to get the int value ( m_4ByteData) using
m_8bitData[4].

Put the stuff into m_8bitData[4] and read the value of m_4ByteData.
In theory, this invokes undefined behaviour, in practice, it works.

You may want to replace the magical constant 4 by sizeof(int) and to
use the type unsigned char for m_8bitData[4].

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de