Rust格式化打印

1.2 Rust格式化打印

打印是通過一系列在標準定義std::fmt其中一些處理包括:

  • format!: 寫格式化的文本到字符串
  • print!: 類似於 format! 但文本打印到控制檯上。
  • println!: 類似於 print! 但追加一個換行符。

以相同的方式解析全部文本。加號是正確的格式將在編譯時進行檢查。

fn main() {
// In general, the `{}` will be automatically replaced with any
// arguments. These will be stringified.
println!("{} days", 31);

// Without a suffix, 31 becomes an i32. You can change what type 31 is,
// with a suffix.

// There are various optional patterns this works with. Positional
// arguments can be used.
println!("{0}, this is {1}. {1}, this is {0}", "Alice", "Bob");

// As can named arguments.
println!("{subject} {verb} {predicate}",
         predicate="over the lazy dog",
         subject="the quick brown fox",
         verb="jumps");

// Special formatting can be specified after a \`:\`.
println!("{} of {:b} people know binary, the other half don't", 1, 2);

// It will even check to make sure the correct number of arguments are
// used.
println!("My name is {0}, {1} {0}", "Bond");
// FIXME ^ Add the missing argument: "James"

// Create a structure which contains an \`i32\`. Name it \`Structure\`.
struct Structure(i32);

// However, custom types such as this structure require more complicated
// handling. This will not work.
println!("This struct \`{}\` won't print...", Structure(3));
// FIXME ^ Comment out this line.

}

std::fmt 包括多個 traits 支配文本的顯示。 兩個重要的基本形式如下:

  • fmt::Debug: 使用 {:?} 標記。格式文本用於調試的目的。
  • fmt::Display: 使用 {} 標記。在一個更優雅的,用戶友好的方式設置文本格式。

這裏, fmt::Display 被使用,因爲std庫提供這些類型。 打印文本自定義類型,需要更多的步驟。

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