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Go string handling overview [cheat sheet]

 3 years ago
source link: https://yourbasic.org/golang/string-functions-reference-cheat-sheet/
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Go string handling overview [cheat sheet]

yourbasic.org/golang
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String literals (escape characters)

Expression Result Note "" Default zero value for type string "Japan 日本" Japan 日本 Go code is Unicode text encoded in UTF‑8 "\xe6\x97\xa5" 日 \xNN specifies a byte "\u65E5" 日 \uNNNN specifies a Unicode value "\\" \ Backslash "\"" " Double quote "\n" Newline "\t" Tab `\xe6` \xe6 Raw string literal* html.EscapeString("<>") <> HTML escape for <, >, &, ' and " url.PathEscape("A B") A%20B URL percent-encoding net/url

* In `` string literals, text is interpreted literally and backslashes have no special meaning. See Escapes and multiline strings for more on raw strings, escape characters and string encodings.

Concatenate

Expression Result Note "Ja" + "pan" Japan Concatenation

Performance tips
See 3 tips for efficient string concatenation for how to best use a string builder to concatenate strings without redundant copying.

Equal and compare (ignore case)

Expression Result Note "Japan" == "Japan" true Equality strings.EqualFold("Japan", "JAPAN") true Unicode case folding "Japan" < "japan" true Lexicographic order

Length in bytes or runes

Expression Result Note len("日") 3 Length in bytes utf8.RuneCountInString("日") 1 in runes unicode/utf8 utf8.ValidString("日") true UTF-8? unicode/utf8

Index, substring, iterate

Expression Result Note "Japan"[2] 'p' Byte at position 2 "Japan"[1:3] ap Byte indexing "Japan"[:2] Ja "Japan"[2:] pan

A Go range loop iterates over UTF-8 encoded characters (runes):

for i, ch := range "Japan 日本" {
    fmt.Printf("%d:%q ", i, ch)
}
// Output: 0:'J' 1:'a' 2:'p' 3:'a' 4:'n' 5:' ' 6:'日' 9:'本'

Iterating over bytes produces nonsense characters for non-ASCII text:

s := "Japan 日本"
for i := 0; i < len(s); i++ {
    fmt.Printf("%q ", s[i])
}
// Output: 'J' 'a' 'p' 'a' 'n' ' ' 'æ' '\u0097' '¥' 'æ' '\u009c' '¬'

Search (contains, prefix/suffix, index)

Expression Result Note strings.Contains("Japan", "abc") false Is abc in Japan? strings.ContainsAny("Japan", "abc") true Is a, b or c in Japan? strings.Count("Banana", "ana") 1 Non-overlapping instances of ana strings.HasPrefix("Japan", "Ja") true Does Japan start with Ja? strings.HasSuffix("Japan", "pan") true Does Japan end with pan? strings.Index("Japan", "abc") -1 Index of first abc strings.IndexAny("Japan", "abc") 1 a, b or c strings.LastIndex("Japan", "abc") -1 Index of last abc strings.LastIndexAny("Japan", "abc") 3 a, b or c

Replace (uppercase/lowercase, trim)

Expression Result Note strings.Replace("foo", "o", ".", 2) f.. Replace first two “o” with “.” Use -1 to replace all f := func(r rune) rune {
    return r + 1
}
strings.Map(f, "ab") bc Apply function to each character strings.ToUpper("Japan") JAPAN Uppercase strings.ToLower("Japan") japan Lowercase strings.Title("ja pan") Ja Pan Initial letters to uppercase strings.TrimSpace(" foo\n") foo Strip leading and trailing white space strings.Trim("foo", "fo") Strip leading and trailing f:s and o:s strings.TrimLeft("foo", "f") oo only leading strings.TrimRight("foo", "o") f only trailing strings.TrimPrefix("foo", "fo") o strings.TrimSuffix("foo", "o") fo

Split by space or comma

Expression Result Note strings.Fields(" a\t b\n") ["a" "b"] Remove white space strings.Split("a,b", ",") ["a" "b"] Remove separator strings.SplitAfter("a,b", ",") ["a," "b"] Keep separator

Join strings with separator

Expression Result Note strings.Join([]string{"a", "b"}, ":") a:b Add separator strings.Repeat("da", 2) dada 2 copies of “da”

Format and convert

Expression Result Note strconv.Itoa(-42) "-42" Int to string strconv.FormatInt(255, 16) "ff" Base 16

Sprintf

The fmt.Sprintf function is often your best friend when formatting data:

s := fmt.Sprintf("%.4f", math.Pi) // s == "3.1416"
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This fmt cheat sheet covers the most common formatting flags.

Regular expressions

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For more advanced string handling, see this Regular expressions tutorial, a gentle introduction to the regexp package with cheat sheet and plenty of examples.

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