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30 lines
1 KiB
Markdown
30 lines
1 KiB
Markdown
# Parts of an Embedded Program
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We will look at the elements that distinguish an embedded Rust program from a desktop program.
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✅ Open the `beginner/apps` folder in VS Code.
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``` console
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$ # or use "File > Open Folder" in VS Code
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$ code beginner/apps
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```
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✅ Then open the `src/bin/hello.rs` file.
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## In the file, you will find the following attributes:
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### `#![no_std]`
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The `#![no_std]` attribute indicates that the program will not make use of the standard library, the `std` crate. Instead it will use the `core` library, a subset of the standard library that does not depend on an underlying operating system (OS).
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### `#![no_main]`
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The `#![no_main]` attribute indicates that the program will use a custom entry point instead of the default `fn main() { .. }` one.
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### `#[entry]`
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The `#[entry]` attribute declares the custom entry point of the program. The entry point must be a divergent function whose return type is the never type `!`. The function is not allowed to return; therefore the program is not allowed to terminate.
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