A Rust crate with a sscanf (inverse of format!()) Macro based on Regex
sscanf is a C-function that takes a String, a format String with placeholders and several
Variables (in the Rust version replaced with Types). It then parses the input String, writing
the values behind the placeholders into the Variables (the Rust version returns a Tuple of
the specified Types). This process can be thought of as reversing a call to format!():
```Rust
let s = format!("Hello {} #{}", "World", 5);
assert_eq!(s, "Hello World #5");
let parsed = sscanf::scanf!(s, "Hello {} #{}", String, usize);
// parsed is Option<(String, usize)>
asserteq!(parsed, Some((String::from("World"), 5)));
As can be seen in the example, `scanf` takes a format String like `format!()`, but instead of
writing the values from the remaining parameters into the `{}` it instead extracts the contents
of the input string. Those parts are then parsed according to the specified Types and returned
as a Tuple, or `None` if the parsing failed or the strings don't match.
Rust
let s = "Random Text";
let parsed = sscanf::scanf!(s, "Hello {} #{}", String, usize);
asserteq!(parsed, None); // "Random Text" and "Hello..." do not match
```
Note that the original C-function (and this Crate) are called sscanf, which is the correct
version in this context. scanf is itself a C-function with the same functionality, but
reading the input from stdin instead of taking a String parameter. The macro itself is called
scanf because that is shorter, can be pronounced without sounding too weird and nobody uses
the stdin version anyway.
More examples of the capabilities of scanf:
```Rust
use sscanf::scanf;
let input = "4-5 t: ftttttrvts"; let parsed = scanf!(input, "{}-{} {}: {}", usize, usize, char, String); assert_eq!(parsed, Some((4, 5, 't', String::from("ftttttrvts"))));
let input = " let input = "Goto N36E21";
let parsed = scanf!(input, "Goto {}{}{}{}", char, usize, char, usize);
assert_eq!(parsed, Some(('N', 36, 'E', 21))); let input = "A Sentence. Another Sentence. Yet more Words with Spaces.";
let parsed = scanf!(input, "{}. {}. {}.", String, String, String);
assert!(parsed.issome());
let (a, b, c) = parsed.unwrap();
asserteq!(a, "A Sentence");
asserteq!(b, "Another Sentence");
asserteq!(c, "Yet more Words with Spaces");
``` The parsing part of this macro has very few limitations, since it replaces the And so on. The actual implementation for numbers tries to take the size of the Type into
account and some other details, but that is the gist of the parsing. This means that any sequence of replacements is possible as long as the Regex finds a
combination that works. In the More Types can easily be added, as long as they implement let input = "[1518-10-08 23:51] Guard #751 begins shift";
let parsed = scanf!(input, "{} Guard #{} begins shift", TimeStamp, usize);
assert_eq!(parsed, Some((TimeStamp{
year: 1518, month: 10, day: 8,
hour: 23, minute: 51
}, 751)));
```{} with a Regular
Expression (regex) that corresponds to that type.
For example:
- char is just one Character (regex ".")
- String is any sequence of Characters (regex ".+")
- Numbers are any sequence of digits (regex "\d+")char, usize, char, usize example above it manages to assign
the N and E to the chars because they cannot be matched by the usizes. If the input
were slightly different then it might have matched the 6 of the 36 or the 2 of the 21
to the second char.Custom Types
scanf works with the most primitive Types from std as well as String by default. The
full list can be seen here: Implementations of RegexRepresentation.FromStr for the parsing
and RegexRepresentation for scanf to obtain the Regex of the Type:
```Rust
struct TimeStamp {
year: usize, month: u8, day: u8,
hour: u8, minute: u8,
}
impl sscanf::RegexRepresentation for TimeStamp {
/// Matches "[year-month-day hour:minute]"
const REGEX: &'static str = r"[\d\d\d\d-\d\d-\d\d \d\d:\d\d]";
}
impl std::str::FromStr for TimeStamp {
// ...
}