The strconv Package

strconv converts strings to and from Go's basic types: integers, floats, booleans, and quoted string literals.

Examples

Itoa and Atoi cover the common decimal case. ParseFloat and FormatFloat mirror them for floating-point values, both returning an error alongside the result.

n, err := strconv.Atoi("42")
fmt.Println(n, err)

s := strconv.Itoa(100)
fmt.Println(s)

f, err := strconv.ParseFloat("3.14159", 64)
fmt.Println(f, err)

fmt.Println(strconv.FormatFloat(f, 'f', 2, 64))

Output

ParseInt and FormatInt take an explicit base, so the same pair of functions covers hex, octal, and binary without a separate function per base.

n, err := strconv.ParseInt("2a", 16, 64)
fmt.Println(n, err)

fmt.Println(strconv.FormatInt(255, 16))
fmt.Println(strconv.FormatInt(10, 2))

u, err := strconv.ParseUint("377", 8, 64)
fmt.Println(u, err)

Output

ParseBool accepts several common spellings of true and false. Quote and Unquote round-trip a Go string literal, escapes included.

b, err := strconv.ParseBool("TRUE")
fmt.Println(b, err)

fmt.Println(strconv.FormatBool(false))

q := strconv.Quote("line one\nline two")
fmt.Println(q)

s, err := strconv.Unquote(q)
fmt.Println(s == "line one\nline two", err)

Output

true 
false
"line one\nline two"
true

A failed parse returns a *strconv.NumError, which carries the failing function name and input alongside the underlying error.

_, err := strconv.Atoi("12x")
fmt.Println(err)

var numErr *strconv.NumError
if errors.As(err, &numErr) {
    fmt.Println(numErr.Func, numErr.Num)
}

Output

strconv.Atoi: parsing "12x": invalid syntax
Atoi 12x

Integer conversions

Function	Description
Itoa(i int) string `strconv.Itoa(42)`	Converts i to a decimal string, shorthand for FormatInt(int64(i), 10)
Atoi(s string) (int, error) `strconv.Atoi("42")`	Parses s as a decimal integer, shorthand for ParseInt(s, 10, 0)
ParseInt(s string, base, bitSize int) (int64, error) `strconv.ParseInt("2a", 16, 64)`	Parses s as a signed integer in the given base and bit size
ParseUint(s string, base, bitSize int) (uint64, error) `strconv.ParseUint("42", 10, 64)`	Parses s as an unsigned integer in the given base and bit size
FormatInt(i int64, base int) string `strconv.FormatInt(255, 16)`	Formats i as a string in the given base
FormatUint(i uint64, base int) string `strconv.FormatUint(255, 16)`	Formats an unsigned integer as a string in the given base
AppendInt(dst []byte, i int64, base int) []byte `strconv.AppendInt(b, 42, 10)`	Appends the formatted integer to dst and returns the extended slice
AppendUint(dst []byte, i uint64, base int) []byte `strconv.AppendUint(b, 42, 10)`	Appends the formatted unsigned integer to dst

Float & complex conversions

Function	Description
ParseFloat(s string, bitSize int) (float64, error) `strconv.ParseFloat("3.14", 64)`	Parses s as a floating-point number
FormatFloat(f float64, fmt byte, prec, bitSize int) string `strconv.FormatFloat(3.14159, 'f', 2, 64)`	Formats f per the given verb byte and precision
AppendFloat(dst []byte, f float64, fmt byte, prec, bitSize int) []byte `strconv.AppendFloat(b, 3.14, 'f', 2, 64)`	Appends the formatted float to dst
ParseComplex(s string, bitSize int) (complex128, error) `strconv.ParseComplex("1+2i", 128)`	Parses s as a complex number
FormatComplex(c complex128, fmt byte, prec, bitSize int) string `strconv.FormatComplex(c, 'f', 2, 128)`	Formats a complex number as a string

Bool conversions

Function	Description
ParseBool(s string) (bool, error) `strconv.ParseBool("true")`	Parses s as a boolean; accepts 1, t, T, TRUE, true, True and the false equivalents
FormatBool(b bool) string `strconv.FormatBool(true)`	Formats b as the string "true" or "false"
AppendBool(dst []byte, b bool) []byte `strconv.AppendBool(b, true)`	Appends the formatted boolean to dst

Quoting & unquoting

Function	Description
Quote(s string) string `strconv.Quote("hi\n")`	Returns a double-quoted Go string literal, escaping non-printable characters
QuoteRune(r rune) string `strconv.QuoteRune('é')`	Returns a single-quoted Go rune literal
QuoteToASCII(s string) string `strconv.QuoteToASCII("héllo")`	Like Quote, but escapes every non-ASCII character
QuoteRuneToASCII(r rune) string `strconv.QuoteRuneToASCII('é')`	Like QuoteRune, but escapes a non-ASCII rune
QuoteToGraphic(s string) string `strconv.QuoteToGraphic("café")`	Like Quote, but leaves printable Unicode characters unescaped
QuoteRuneToGraphic(r rune) string `strconv.QuoteRuneToGraphic('é')`	Like QuoteRune, but leaves a graphic rune unescaped
AppendQuote(dst []byte, s string) []byte `strconv.AppendQuote(b, "hi")`	Appends a quoted string to dst
AppendQuoteRune(dst []byte, r rune) []byte `strconv.AppendQuoteRune(b, 'a')`	Appends a quoted rune to dst
AppendQuoteToASCII(dst []byte, s string) []byte `strconv.AppendQuoteToASCII(b, "héllo")`	Appends an ASCII-escaped quoted string to dst
AppendQuoteRuneToASCII(dst []byte, r rune) []byte `strconv.AppendQuoteRuneToASCII(b, 'é')`	Appends an ASCII-escaped quoted rune to dst
AppendQuoteToGraphic(dst []byte, s string) []byte `strconv.AppendQuoteToGraphic(b, "café")`	Appends a graphic-preserving quoted string to dst
AppendQuoteRuneToGraphic(dst []byte, r rune) []byte `strconv.AppendQuoteRuneToGraphic(b, 'é')`	Appends a graphic-preserving quoted rune to dst
Unquote(s string) (string, error) strconv.Unquote(`"hi\n"`)	Interprets s as a single-quoted, double-quoted, or backquoted Go string literal
UnquoteChar(s string, quote byte) (value rune, multibyte bool, tail string, err error) strconv.UnquoteChar(`\n`, 0)	Decodes the first character or escape sequence in s
QuotedPrefix(s string) (string, error) strconv.QuotedPrefix(`"hi" rest`)	Returns the quoted string at the start of s, without unquoting it

Predicates

Function	Description
CanBackquote(s string) bool `strconv.CanBackquote("hi")`	Reports whether s can be represented unchanged as a backquoted string
IsPrint(r rune) bool `strconv.IsPrint('a')`	Reports whether r is defined as printable by Go's rules
IsGraphic(r rune) bool `strconv.IsGraphic('a')`	Reports whether r is defined as a Unicode graphic character

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