打印是通过一系列在标准定义std::fmt其中一些宏处理包括：
format!: 写格式化的文本到字符串
print!: 类似于 format! 但文本打印到控制台上。
println!: 类似于 print! 但追加一个换行符。
以相同的方式解析全部文本。加号是正确的格式将在编译时进行检查。
| 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 包括多个 traits 支配文本的显示。 两个重要的基本形式如下：
fmt::Debug: 使用 {:?} 标记。格式文本用于调试的目的。
fmt::Display: 使用 {} 标记。在一个更优雅的，用户友好的方式设置文本格式。
这里, fmt::Display 被使用，因为std库提供这些类型。 打印文本自定义类型，需要更多的步骤。
