readfile1-rs
This is just an example of a rust program that uses the standard IO module to read a file into a vector data structure, demonstrating the complexity (compared to C) of handling error conditions.
Once the file is read, the program prints out how many bytes were read and a classic hex dump of the file's bytes with the printable ASCII representation on the right. Example:
reading file name: ../sierpinski-rs/img/sierpinski.png.. 2229 bytes read.
simple hexdump (dot <.> denotes unprintable char)
87654321 00 11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff |0123456789abcdef|
-------- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- |----------------|
00000000 89 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 |.PNG........IHDR|
00000010 00 00 00 c8 00 00 00 96 08 00 00 00 00 be b7 98 |................|
00000020 c5 00 00 08 7c 49 44 41 54 78 01 ed 5c 5b 96 a3 |....|IDATx..\[..|
00000030 3a 0c 64 f6 bf 68 a6 e4 f2 43 22 56 b0 c0 4e 27 |:.d..h...C"V..N'|
00000040 dd b9 87 08 bd 55 65 9b 90 9e 8f fb 6f db b7 d5 |.....Ue.....o...|
00000050 ff bd 62 c6 f6 ef 15 3c b6 57 ac d6 97 c8 e8 81 |..b....<.W......|
...
00000890 a2 46 2f 24 cd 26 e1 e2 95 5d 8d 48 76 7c ea ed |.F/$.&...].Hv|..|
000008a0 3f cd de 5b 3f c2 2c 40 9c 00 00 00 00 49 45 4e |?..[?.,@.....IEN|
000008b0 44 ae 42 60 82 |D.B`.|
hexdump of 2229 (0x8b5) bytes completed.
This demonstrates the use of std:env:args(), std::fs::File::open and how to:
- handle a function which returns Option type like std::env::args().nth()
- Option types return Some() / None
- handle a function which returns a Result type like fs::File::open()
- Result types return Ok() / Err()
- use low level file IO from rust
- populate a buffer safely leveraging the vector (Vec) built in type
- how to use match with error handling
You can run the program using cargo like this:
$ cargo run <filename>Examples of error and ok results:
- no argument given specifying the file name to read:
$ cargo run
Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
Running `target/debug/readfile1-rs`
thread 'main' panicked at 'no file argument present', main.rs:28:12
note: Run with `RUST_BACKTRACE=1` for a backtrace.- argument given, but file cannot be opened because it is missing or unreadable:
$ cargo run bad_fname
Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
Running `target/debug/readfile1-rs bad_fname`
thread 'main' panicked at 'failed to open file: No such file or directory (os error 2)', main.rs:23:20
note: Run with `RUST_BACKTRACE=1` for a backtrace.- successful file read (I just passed in this project's Cargo.toml file):
$ cargo run ./Cargo.toml
Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
Running `target/debug/readfile1-rs ./Cargo.toml`
reading file name: ./Cargo.toml.. 112 bytes read.
simple hexdump (dot <.> denotes unprintable char)
87654321 00 11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff |0123456789abcdef|
-------- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- |----------------|
00000000 5b 70 61 63 6b 61 67 65 5d 0a 6e 61 6d 65 20 3d |[package].name =|
00000010 20 22 72 65 61 64 66 69 6c 65 31 2d 72 73 22 0a | "readfile1-rs".|
00000020 76 65 72 73 69 6f 6e 20 3d 20 22 30 2e 31 2e 30 |version = "0.1.0|
00000030 22 0a 61 75 74 68 6f 72 73 20 3d 20 5b 22 44 61 |".authors = ["Da|
00000040 6e 20 4d 61 63 6b 20 3c 6d 61 63 6b 40 6d 61 63 |n Mack <mack@mac|
00000050 6b 74 72 6f 6e 69 63 73 2e 63 6f 6d 3e 22 5d 0a |ktronics.com>"].|
00000060 0a 5b 64 65 70 65 6e 64 65 6e 63 69 65 73 5d 0a |.[dependencies].|
hexdump of 112 bytes completed.Hope this is useful. Error handling in rust is more powerful but comes with a bit more complexity.
This worked with rust version 1.20.