single
Pack
メニューを表示するにはスワイプしてください
Using #pragma pack can reduce the overall size of a structure or ensure precise alignment for specific cases, such as network protocols or hardware interfaces.
main.c
1234567891011121314#include <stdio.h> #include <stdint.h> // Without using `#pragma pack` struct Packet { uint8_t flag; // 8 bits or 1 bytes uint16_t length; // 16 bits or 2 bytes uint8_t type; // 8 bits or 1 bytes }; int main() { printf("Size without packing: %zu bytes\n", sizeof(struct Packet)); return 0; }
As you may recall, structure alignment is determined by the largest field within the structure.
Using #pragma pack
main.c
123456789101112131415#include <stdio.h> #include <stdint.h> #pragma pack(push, 1) struct PacketPacked { uint8_t flag; // 8 bits = 1 bytes uint16_t length; // 16 bits == 2 bytes uint8_t type; // 8 bits == 1 bytes }; #pragma pack(pop) int main() { printf("Size with packing: %zu bytes\n", sizeof(struct PacketPacked)); return 0; }
The directive #pragma pack(push, 1) creates a local alignment context for a structure.
You start a new alignment scope with push, apply a specific rule (here, 1-byte alignment), define the structure, then restore the previous alignment with pop.
Using push with 1 ensures that all fields are aligned on 1-byte boundaries, with no padding between them.
スワイプしてコーディングを開始
You're working with a digital sensor that sends binary data packets over UART. Each packet follows a fixed 4-byte layout. To match this exact layout with no padding, use the #pragma pack directive to enforce 1-byte alignment.
| Bytes | Field | Type |
|---|---|---|
| 1 | Command code | uint8_t |
| 2 | Sensor value | uint16_t |
| 1 | Checksum | uint8_t |
- Fill in the first
___to start the packed context with 1-byte alignment. - Fill in the second
___to restore default alignment after the struct. - Use the correct field access expressions (e.g.
packet.cmd) in eachprintfto output: the command byte, the 2-byte value and the checksum byte.
解答
実践的な練習のためにデスクトップに切り替える下記のオプションのいずれかを利用して、現在の場所から続行するフィードバックありがとうございます！
single
AIに質問する
AIに質問する
何でも質問するか、提案された質問の1つを試してチャットを始めてください
