Struct packing and alignment in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a packed struct in C.

Embedded C

struct __attribute__(([1])) PackedData {
    char a;
    int b;
};

Drag options to blanks, or click blank then click option'

Aaligned

Bunused

Cdeprecated

Dpacked

Attempts:

3 left

💡 Hint

Common Mistakes

Using __attribute__((aligned)) instead of packed

Forgetting to use attribute at all

The __attribute__((packed)) tells the compiler to pack the struct without padding bytes.

2fill in blank

medium

Complete the code to specify 1-byte alignment for the struct.

Embedded C

struct Data {
    char a;
    int b;
} __attribute__(([1](1)));

Drag options to blanks, or click blank then click option'

Apacked

Baligned

Cdeprecated

Dunused

Attempts:

3 left

💡 Hint

Common Mistakes

Using packed instead of aligned

Not specifying the alignment value

The __attribute__((aligned(1))) forces the struct to have 1-byte alignment, minimizing padding.

3fill in blank

hard

Fix the error in the struct declaration to correctly pack the struct.

Embedded C

struct Data {
    char a;
    int b;
} __attribute__(([1]));

Drag options to blanks, or click blank then click option'

Apacked

Balign

Calignas

Dpack

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'align' or 'pack' which are invalid

Confusing with C++11 alignas keyword

The correct attribute to pack a struct is packed. Other options are invalid or incorrect.

4fill in blank

hard

Fill both blanks to create a struct with 2-byte alignment and packed attribute.

Embedded C

struct Data {
    char a;
    short b;
} __attribute__(([1])) __attribute__(([2](2)));

Drag options to blanks, or click blank then click option'

Apacked

Baligned

Cdeprecated

Dunused

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the attributes

Using deprecated or unused attributes

Use packed to remove padding and aligned(2) to set 2-byte alignment.

5fill in blank

hard

Fill all three blanks to define a packed struct with 4-byte alignment and a member with 2-byte alignment.

Embedded C

struct Data {
    char a;
    short b __attribute__(([1](2)));
} __attribute__(([2])) __attribute__(([3](4)));

Drag options to blanks, or click blank then click option'

Aaligned

Bpacked

Cdeprecated

Dunused

Attempts:

3 left

💡 Hint

Common Mistakes

Using packed on member instead of aligned

Misordering attributes

The member b is aligned to 2 bytes, the struct is packed and aligned to 4 bytes.