CC1352R: Implementation of a Union

Ilian Chakarov

Expert 2170 points

Part Number: CC1352R

Hi,

IDE CCS Version: 9.3.0.00012

Compiler: TI v18.12.15

Implementing the next Union:

union
{
unsigned int data;
unsigned short data_1;
unsigned short data_2;
unsigned char data_buf[4];
}u_data;

data_buf [0] = 0xaa;

data_buf [1] = 0xbb;

data_buf [2] = 0xcc;

data_buf [3] = 0xdd;

I expect data to be - 0xddccbbaa and it is correct.

data_1 to be 0xddcc

data_2 to be 0xbbaa

Here is the problem. data_1 == data_2 -> 0xbbaa. In the debuger data_ and data_2 have the same address?

What is the problem

Best regards,

Ilian

over 4 years ago

0 George Mock over 4 years ago

TI__Guru**** 249870 points

Ilian Chakarov said:
data_ and data_2 have the same address?

Yes, they do. Every member of a union has the same address. See this FAQ (not from TI).

Thanks and regards,

-George

0 Ilian Chakarov over 4 years ago in reply to George Mock

Expert 2170 points

Yes, but why the value of the data_1 and data_2 are the same, they are unsigned short?

Best regards,

Ilian

+1 George Mock over 4 years ago in reply to Ilian Chakarov

TI__Guru**** 249870 points

Ilian Chakarov said:
why the value of the data_1 and data_2 are the same

Because they have the same type and the same address. Because every member of a union has the same address, there is no good reason for multiple members to have the same type. The specification of the C language allows it, even though it is not useful.

You probably need to change this union to something similar to ...

union
{
    unsigned int data;

    struct tag_struct_inside_union
    {
        unsigned short data_1;
        unsigned short data_2;
    } s;

    unsigned char data_buf[4];
} u_data;

A reference to one of those short members looks like u_data.s.data_1;

Thanks and regards,

-George

0 Ilian Chakarov over 4 years ago in reply to George Mock

Expert 2170 points

Hi thanks,

Best regards,

Ilian

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CC1352R: Implementation of a Union