Go字串格式化範例

Go語言為printf傳統中的字串格式化提供了極好的支援。 以下是常見字串格式化任務的一些範例。

Go提供了幾種列印「動詞」，設計用於格式化一般的值。 例如，列印 point 結構的一個範例。

如果值是一個結構體，%+v變體將包括結構體的欄位名。

%#v變體列印值的Go語法表示，即將生成該值的原始碼片段。

要列印值的型別，請使用 %T 。格式化布林是比較直截了當的。有許多格式化整數的選項。對於標準的base-10格式化，請使用％d。

具體的每個函式，可參考範例中的程式碼 -

所有的範例程式碼，都放在 F:\worksp\golang 目錄下。安裝Go程式設計環境請參考：/2/23/798.html

string-formatting.go的完整程式碼如下所示 -

package main

import "fmt"
import "os"

type point struct {
    x, y int
}

func main() {

    // Go offers several printing "verbs" designed to
    // format general Go values. For example, this prints
    // an instance of our `point` struct.
    p := point{1, 2}
    fmt.Printf("%v\n", p)

    // If the value is a struct, the `%+v` variant will
    // include the struct's field names.
    fmt.Printf("%+v\n", p)

    // The `%#v` variant prints a Go syntax representation
    // of the value, i.e. the source code snippet that
    // would produce that value.
    fmt.Printf("%#v\n", p)

    // To print the type of a value, use `%T`.
    fmt.Printf("%T\n", p)

    // Formatting booleans is straight-forward.
    fmt.Printf("%t\n", true)

    // There are many options for formatting integers.
    // Use `%d` for standard, base-10 formatting.
    fmt.Printf("%d\n", 123)

    // This prints a binary representation.
    fmt.Printf("%b\n", 14)

    // This prints the character corresponding to the
    // given integer.
    fmt.Printf("%c\n", 33)

    // `%x` provides hex encoding.
    fmt.Printf("%x\n", 456)

    // There are also several formatting options for
    // floats. For basic decimal formatting use `%f`.
    fmt.Printf("%f\n", 78.9)

    // `%e` and `%E` format the float in (slightly
    // different versions of) scientific notation.
    fmt.Printf("%e\n", 123400000.0)
    fmt.Printf("%E\n", 123400000.0)

    // For basic string printing use `%s`.
    fmt.Printf("%s\n", "\"string\"")

    // To double-quote strings as in Go source, use `%q`.
    fmt.Printf("%q\n", "\"string\"")

    // As with integers seen earlier, `%x` renders
    // the string in base-16, with two output characters
    // per byte of input.
    fmt.Printf("%x\n", "hex this")

    // To print a representation of a pointer, use `%p`.
    fmt.Printf("%p\n", &p)

    // When formatting numbers you will often want to
    // control the width and precision of the resulting
    // figure. To specify the width of an integer, use a
    // number after the `%` in the verb. By default the
    // result will be right-justified and padded with
    // spaces.
    fmt.Printf("|%6d|%6d|\n", 12, 345)

    // You can also specify the width of printed floats,
    // though usually you'll also want to restrict the
    // decimal precision at the same time with the
    // width.precision syntax.
    fmt.Printf("|%6.2f|%6.2f|\n", 1.2, 3.45)

    // To left-justify, use the `-` flag.
    fmt.Printf("|%-6.2f|%-6.2f|\n", 1.2, 3.45)

    // You may also want to control width when formatting
    // strings, especially to ensure that they align in
    // table-like output. For basic right-justified width.
    fmt.Printf("|%6s|%6s|\n", "foo", "b")

    // To left-justify use the `-` flag as with numbers.
    fmt.Printf("|%-6s|%-6s|\n", "foo", "b")

    // So far we've seen `Printf`, which prints the
    // formatted string to `os.Stdout`. `Sprintf` formats
    // and returns a string without printing it anywhere.
    s := fmt.Sprintf("a %s", "string")
    fmt.Println(s)

    // You can format+print to `io.Writers` other than
    // `os.Stdout` using `Fprintf`.
    fmt.Fprintf(os.Stderr, "an %s\n", "error")
}

執行上面程式碼，將得到以下輸出結果 -

F:\worksp\golang>go run string-formatting.go
{1 2}
{x:1 y:2}
main.point{x:1, y:2}
main.point
true
123
1110
!
1c8
78.900000
1.234000e+08
1.234000E+08
"string"
"\"string\""
6865782074686973
0xc042004280
|    12|   345|
|  1.20|  3.45|
|1.20  |3.45  |
|   foo|     b|
|foo   |b     |
a string
an error