strconv - ActiveState ActiveGo 1.8
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Package strconv

import "strconv"
Overview
Index
Examples

Overview ▾

Package strconv implements conversions to and from string representations of basic data types.

Numeric Conversions

The most common numeric conversions are Atoi (string to int) and Itoa (int to string). 

i, err := strconv.Atoi("-42")
s := strconv.Itoa(-42)

These assume decimal and the Go int type.

ParseBool, ParseFloat, ParseInt, and ParseUint convert strings to values: 

b, err := strconv.ParseBool("true")
f, err := strconv.ParseFloat("3.1415", 64)
i, err := strconv.ParseInt("-42", 10, 64)
u, err := strconv.ParseUint("42", 10, 64)

The parse functions return the widest type (float64, int64, and uint64), but if the size argument specifies a narrower width the result can be converted to that narrower type without data loss: 

s := "2147483647" // biggest int32
i64, err := strconv.ParseInt(s, 10, 32)
...
i := int32(i64)

FormatBool, FormatFloat, FormatInt, and FormatUint convert values to strings: 

s := strconv.FormatBool(true)
s := strconv.FormatFloat(3.1415, 'E', -1, 64)
s := strconv.FormatInt(-42, 16)
s := strconv.FormatUint(42, 16)

AppendBool, AppendFloat, AppendInt, and AppendUint are similar but append the formatted value to a destination slice.

String Conversions

Quote and QuoteToASCII convert strings to quoted Go string literals. The latter guarantees that the result is an ASCII string, by escaping any non-ASCII Unicode with \u: 

q := Quote("Hello, 世界")
q := QuoteToASCII("Hello, 世界")

QuoteRune and QuoteRuneToASCII are similar but accept runes and return quoted Go rune literals.

Unquote and UnquoteChar unquote Go string and rune literals.

Index ▾

Constants
Variables
func AppendBool(dst []byte, b bool) []byte
func AppendFloat(dst []byte, f float64, fmt byte, prec, bitSize int) []byte
func AppendInt(dst []byte, i int64, base int) []byte
func AppendQuote(dst []byte, s string) []byte
func AppendQuoteRune(dst []byte, r rune) []byte
func AppendQuoteRuneToASCII(dst []byte, r rune) []byte
func AppendQuoteRuneToGraphic(dst []byte, r rune) []byte
func AppendQuoteToASCII(dst []byte, s string) []byte
func AppendQuoteToGraphic(dst []byte, s string) []byte
func AppendUint(dst []byte, i uint64, base int) []byte
func Atoi(s string) (int, error)
func CanBackquote(s string) bool
func FormatBool(b bool) string
func FormatFloat(f float64, fmt byte, prec, bitSize int) string
func FormatInt(i int64, base int) string
func FormatUint(i uint64, base int) string
func IsGraphic(r rune) bool
func IsPrint(r rune) bool
func Itoa(i int) string
func ParseBool(str string) (bool, error)
func ParseFloat(s string, bitSize int) (float64, error)
func ParseInt(s string, base int, bitSize int) (i int64, err error)
func ParseUint(s string, base int, bitSize int) (uint64, error)
func Quote(s string) string
func QuoteRune(r rune) string
func QuoteRuneToASCII(r rune) string
func QuoteRuneToGraphic(r rune) string
func QuoteToASCII(s string) string
func QuoteToGraphic(s string) string
func Unquote(s string) (string, error)
func UnquoteChar(s string, quote byte) (value rune, multibyte bool, tail string, err error)
type NumError
    func (e *NumError) Error() string

Package files

atob.go atof.go atoi.go decimal.go doc.go extfloat.go ftoa.go isprint.go itoa.go quote.go

Constants

IntSize is the size in bits of an int or uint value. 

const IntSize = intSize

Variables

ErrRange indicates that a value is out of range for the target type. 

var ErrRange = errors.New("value out of range")

ErrSyntax indicates that a value does not have the right syntax for the target type. 

var ErrSyntax = errors.New("invalid syntax")

func AppendBool 

func AppendBool(dst []byte, b bool) []byte

AppendBool appends "true" or "false", according to the value of b, to dst and returns the extended buffer.

▾ Example

Code:

b := []byte("bool:")
b = strconv.AppendBool(b, true)
fmt.Println(string(b))

Output:

bool:true

func AppendFloat 

func AppendFloat(dst []byte, f float64, fmt byte, prec, bitSize int) []byte

AppendFloat appends the string form of the floating-point number f, as generated by FormatFloat, to dst and returns the extended buffer.

▾ Example

Code:

b32 := []byte("float32:")
b32 = strconv.AppendFloat(b32, 3.1415926535, 'E', -1, 32)
fmt.Println(string(b32))

b64 := []byte("float64:")
b64 = strconv.AppendFloat(b64, 3.1415926535, 'E', -1, 64)
fmt.Println(string(b64))

Output:

float32:3.1415927E+00
float64:3.1415926535E+00

func AppendInt 

func AppendInt(dst []byte, i int64, base int) []byte

AppendInt appends the string form of the integer i, as generated by FormatInt, to dst and returns the extended buffer.

▾ Example

Code:

b10 := []byte("int (base 10):")
b10 = strconv.AppendInt(b10, -42, 10)
fmt.Println(string(b10))

b16 := []byte("int (base 16):")
b16 = strconv.AppendInt(b16, -42, 16)
fmt.Println(string(b16))

Output:

int (base 10):-42
int (base 16):-2a

func AppendQuote 

func AppendQuote(dst []byte, s string) []byte

AppendQuote appends a double-quoted Go string literal representing s, as generated by Quote, to dst and returns the extended buffer.

▾ Example

Code:

b := []byte("quote:")
b = strconv.AppendQuote(b, `"Fran & Freddie's Diner"`)
fmt.Println(string(b))

Output:

quote:"\"Fran & Freddie's Diner\""

func AppendQuoteRune 

func AppendQuoteRune(dst []byte, r rune) []byte

AppendQuoteRune appends a single-quoted Go character literal representing the rune, as generated by QuoteRune, to dst and returns the extended buffer.

▾ Example

Code:

b := []byte("rune:")
b = strconv.AppendQuoteRune(b, '☺')
fmt.Println(string(b))

Output:

rune:'☺'

func AppendQuoteRuneToASCII 

func AppendQuoteRuneToASCII(dst []byte, r rune) []byte

AppendQuoteRuneToASCII appends a single-quoted Go character literal representing the rune, as generated by QuoteRuneToASCII, to dst and returns the extended buffer.

▾ Example

Code:

b := []byte("rune (ascii):")
b = strconv.AppendQuoteRuneToASCII(b, '☺')
fmt.Println(string(b))

Output:

rune (ascii):'\u263a'

func AppendQuoteRuneToGraphic 

func AppendQuoteRuneToGraphic(dst []byte, r rune) []byte

AppendQuoteRuneToGraphic appends a single-quoted Go character literal representing the rune, as generated by QuoteRuneToGraphic, to dst and returns the extended buffer.

func AppendQuoteToASCII 

func AppendQuoteToASCII(dst []byte, s string) []byte

AppendQuoteToASCII appends a double-quoted Go string literal representing s, as generated by QuoteToASCII, to dst and returns the extended buffer.

▾ Example

Code:

b := []byte("quote (ascii):")
b = strconv.AppendQuoteToASCII(b, `"Fran & Freddie's Diner"`)
fmt.Println(string(b))

Output:

quote (ascii):"\"Fran & Freddie's Diner\""

func AppendQuoteToGraphic 

func AppendQuoteToGraphic(dst []byte, s string) []byte

AppendQuoteToGraphic appends a double-quoted Go string literal representing s, as generated by QuoteToGraphic, to dst and returns the extended buffer.

func AppendUint 

func AppendUint(dst []byte, i uint64, base int) []byte

AppendUint appends the string form of the unsigned integer i, as generated by FormatUint, to dst and returns the extended buffer.

▾ Example

Code:

b10 := []byte("uint (base 10):")
b10 = strconv.AppendUint(b10, 42, 10)
fmt.Println(string(b10))

b16 := []byte("uint (base 16):")
b16 = strconv.AppendUint(b16, 42, 16)
fmt.Println(string(b16))

Output:

uint (base 10):42
uint (base 16):2a

func Atoi 

func Atoi(s string) (int, error)

Atoi returns the result of ParseInt(s, 10, 0) converted to type int.

▾ Example

Code:

v := "10"
if s, err := strconv.Atoi(v); err == nil {
    fmt.Printf("%T, %v", s, s)
}

Output:

int, 10

func CanBackquote 

func CanBackquote(s string) bool

CanBackquote reports whether the string s can be represented unchanged as a single-line backquoted string without control characters other than tab.

▾ Example

Code:

fmt.Println(strconv.CanBackquote("Fran & Freddie's Diner ☺"))
fmt.Println(strconv.CanBackquote("`can't backquote this`"))

Output:

true
false

func FormatBool 

func FormatBool(b bool) string

FormatBool returns "true" or "false" according to the value of b

▾ Example

Code:

v := true
s := strconv.FormatBool(v)
fmt.Printf("%T, %v\n", s, s)

Output:

string, true

func FormatFloat 

func FormatFloat(f float64, fmt byte, prec, bitSize int) string

FormatFloat converts the floating-point number f to a string, according to the format fmt and precision prec. It rounds the result assuming that the original was obtained from a floating-point value of bitSize bits (32 for float32, 64 for float64).

The format fmt is one of 'b' (-ddddp±ddd, a binary exponent), 'e' (-d.dddde±dd, a decimal exponent), 'E' (-d.ddddE±dd, a decimal exponent), 'f' (-ddd.dddd, no exponent), 'g' ('e' for large exponents, 'f' otherwise), or 'G' ('E' for large exponents, 'f' otherwise).

The precision prec controls the number of digits (excluding the exponent) printed by the 'e', 'E', 'f', 'g', and 'G' formats. For 'e', 'E', and 'f' it is the number of digits after the decimal point. For 'g' and 'G' it is the total number of digits. The special precision -1 uses the smallest number of digits necessary such that ParseFloat will return f exactly.

▾ Example

Code:

v := 3.1415926535

s32 := strconv.FormatFloat(v, 'E', -1, 32)
fmt.Printf("%T, %v\n", s32, s32)

s64 := strconv.FormatFloat(v, 'E', -1, 64)
fmt.Printf("%T, %v\n", s64, s64)

Output:

string, 3.1415927E+00
string, 3.1415926535E+00

func FormatInt 

func FormatInt(i int64, base int) string

FormatInt returns the string representation of i in the given base, for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z' for digit values >= 10.

▾ Example

Code:

v := int64(-42)

s10 := strconv.FormatInt(v, 10)
fmt.Printf("%T, %v\n", s10, s10)

s16 := strconv.FormatInt(v, 16)
fmt.Printf("%T, %v\n", s16, s16)

Output:

string, -42
string, -2a

func FormatUint 

func FormatUint(i uint64, base int) string

FormatUint returns the string representation of i in the given base, for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z' for digit values >= 10.

▾ Example

Code:

v := uint64(42)

s10 := strconv.FormatUint(v, 10)
fmt.Printf("%T, %v\n", s10, s10)

s16 := strconv.FormatUint(v, 16)
fmt.Printf("%T, %v\n", s16, s16)

Output:

string, 42
string, 2a

func IsGraphic 

func IsGraphic(r rune) bool

IsGraphic reports whether the rune is defined as a Graphic by Unicode. Such characters include letters, marks, numbers, punctuation, symbols, and spaces, from categories L, M, N, P, S, and Zs.

func IsPrint 

func IsPrint(r rune) bool

IsPrint reports whether the rune is defined as printable by Go, with the same definition as unicode.IsPrint: letters, numbers, punctuation, symbols and ASCII space.

▾ Example

Code:

c := strconv.IsPrint('\u263a')
fmt.Println(c)

bel := strconv.IsPrint('\007')
fmt.Println(bel)

Output:

true
false

func Itoa 

func Itoa(i int) string

Itoa is shorthand for FormatInt(int64(i), 10).

▾ Example

Code:

i := 10
s := strconv.Itoa(i)
fmt.Printf("%T, %v\n", s, s)

Output:

string, 10

func ParseBool 

func ParseBool(str string) (bool, error)

ParseBool returns the boolean value represented by the string. It accepts 1, t, T, TRUE, true, True, 0, f, F, FALSE, false, False. Any other value returns an error.

▾ Example

Code:

v := "true"
if s, err := strconv.ParseBool(v); err == nil {
    fmt.Printf("%T, %v\n", s, s)
}

Output:

bool, true

func ParseFloat 

func ParseFloat(s string, bitSize int) (float64, error)

ParseFloat converts the string s to a floating-point number with the precision specified by bitSize: 32 for float32, or 64 for float64. When bitSize=32, the result still has type float64, but it will be convertible to float32 without changing its value.

If s is well-formed and near a valid floating point number, ParseFloat returns the nearest floating point number rounded using IEEE754 unbiased rounding.

The errors that ParseFloat returns have concrete type *NumError and include err.Num = s.

If s is not syntactically well-formed, ParseFloat returns err.Err = ErrSyntax.

If s is syntactically well-formed but is more than 1/2 ULP away from the largest floating point number of the given size, ParseFloat returns f = ±Inf, err.Err = ErrRange.

▾ Example

Code:

v := "3.1415926535"
if s, err := strconv.ParseFloat(v, 32); err == nil {
    fmt.Printf("%T, %v\n", s, s)
}
if s, err := strconv.ParseFloat(v, 64); err == nil {
    fmt.Printf("%T, %v\n", s, s)
}

Output:

float64, 3.1415927410125732
float64, 3.1415926535

func ParseInt 

func ParseInt(s string, base int, bitSize int) (i int64, err error)

ParseInt interprets a string s in the given base (2 to 36) and returns the corresponding value i. If base == 0, the base is implied by the string's prefix: base 16 for "0x", base 8 for "0", and base 10 otherwise.

The bitSize argument specifies the integer type that the result must fit into. Bit sizes 0, 8, 16, 32, and 64 correspond to int, int8, int16, int32, and int64.

The errors that ParseInt returns have concrete type *NumError and include err.Num = s. If s is empty or contains invalid digits, err.Err = ErrSyntax and the returned value is 0; if the value corresponding to s cannot be represented by a signed integer of the given size, err.Err = ErrRange and the returned value is the maximum magnitude integer of the appropriate bitSize and sign.

▾ Example

Code:

v32 := "-354634382"
if s, err := strconv.ParseInt(v32, 10, 32); err == nil {
    fmt.Printf("%T, %v\n", s, s)
}
if s, err := strconv.ParseInt(v32, 16, 32); err == nil {
    fmt.Printf("%T, %v\n", s, s)
}

v64 := "-3546343826724305832"
if s, err := strconv.ParseInt(v64, 10, 64); err == nil {
    fmt.Printf("%T, %v\n", s, s)
}
if s, err := strconv.ParseInt(v64, 16, 64); err == nil {
    fmt.Printf("%T, %v\n", s, s)
}

Output:

int64, -354634382
int64, -3546343826724305832

func ParseUint 

func ParseUint(s string, base int, bitSize int) (uint64, error)

ParseUint is like ParseInt but for unsigned numbers.

▾ Example

Code:

v := "42"
if s, err := strconv.ParseUint(v, 10, 32); err == nil {
    fmt.Printf("%T, %v\n", s, s)
}
if s, err := strconv.ParseUint(v, 10, 64); err == nil {
    fmt.Printf("%T, %v\n", s, s)
}

Output:

uint64, 42
uint64, 42

func Quote 

func Quote(s string) string

Quote returns a double-quoted Go string literal representing s. The returned string uses Go escape sequences (\t, \n, \xFF, \u0100) for control characters and non-printable characters as defined by IsPrint.

▾ Example

Code:

s := strconv.Quote(`"Fran & Freddie's Diner	☺"`)
fmt.Println(s)

Output:

"\"Fran & Freddie's Diner\t☺\""

func QuoteRune 

func QuoteRune(r rune) string

QuoteRune returns a single-quoted Go character literal representing the rune. The returned string uses Go escape sequences (\t, \n, \xFF, \u0100) for control characters and non-printable characters as defined by IsPrint.

▾ Example

Code:

s := strconv.QuoteRune('☺')
fmt.Println(s)

Output:

'☺'

func QuoteRuneToASCII 

func QuoteRuneToASCII(r rune) string

QuoteRuneToASCII returns a single-quoted Go character literal representing the rune. The returned string uses Go escape sequences (\t, \n, \xFF, \u0100) for non-ASCII characters and non-printable characters as defined by IsPrint.

▾ Example

Code:

s := strconv.QuoteRuneToASCII('☺')
fmt.Println(s)

Output:

'\u263a'

func QuoteRuneToGraphic 

func QuoteRuneToGraphic(r rune) string

QuoteRuneToGraphic returns a single-quoted Go character literal representing the rune. The returned string uses Go escape sequences (\t, \n, \xFF, \u0100) for non-ASCII characters and non-printable characters as defined by IsGraphic.

func QuoteToASCII 

func QuoteToASCII(s string) string

QuoteToASCII returns a double-quoted Go string literal representing s. The returned string uses Go escape sequences (\t, \n, \xFF, \u0100) for non-ASCII characters and non-printable characters as defined by IsPrint.

▾ Example

Code:

s := strconv.QuoteToASCII(`"Fran & Freddie's Diner	☺"`)
fmt.Println(s)

Output:

"\"Fran & Freddie's Diner\t\u263a\""

func QuoteToGraphic 

func QuoteToGraphic(s string) string

QuoteToGraphic returns a double-quoted Go string literal representing s. The returned string uses Go escape sequences (\t, \n, \xFF, \u0100) for non-ASCII characters and non-printable characters as defined by IsGraphic.

func Unquote 

func Unquote(s string) (string, error)

Unquote interprets s as a single-quoted, double-quoted, or backquoted Go string literal, returning the string value that s quotes. (If s is single-quoted, it would be a Go character literal; Unquote returns the corresponding one-character string.)

▾ Example

Code:

test := func(s string) {
    t, err := strconv.Unquote(s)
    if err != nil {
        fmt.Printf("Unquote(%#v): %v\n", s, err)
    } else {
        fmt.Printf("Unquote(%#v) = %v\n", s, t)
    }
}

s := `\"Fran & Freddie's Diner\t\u263a\"\"`
// If the string doesn't have quotes, it can't be unquoted.
test(s) // invalid syntax
test("`" + s + "`")
test(`"` + s + `"`)
test(`'\u263a'`)

Output:

Unquote("\\\"Fran & Freddie's Diner\\t\\u263a\\\"\\\""): invalid syntax
Unquote("`\\\"Fran & Freddie's Diner\\t\\u263a\\\"\\\"`") = \"Fran & Freddie's Diner\t\u263a\"\"
Unquote("\"\\\"Fran & Freddie's Diner\\t\\u263a\\\"\\\"\"") = "Fran & Freddie's Diner	☺""
Unquote("'\\u263a'") = ☺

func UnquoteChar 

func UnquoteChar(s string, quote byte) (value rune, multibyte bool, tail string, err error)

UnquoteChar decodes the first character or byte in the escaped string or character literal represented by the string s. It returns four values: 

1) value, the decoded Unicode code point or byte value;
2) multibyte, a boolean indicating whether the decoded character requires a multibyte UTF-8 representation;
3) tail, the remainder of the string after the character; and
4) an error that will be nil if the character is syntactically valid.

The second argument, quote, specifies the type of literal being parsed and therefore which escaped quote character is permitted. If set to a single quote, it permits the sequence \' and disallows unescaped '. If set to a double quote, it permits \" and disallows unescaped ". If set to zero, it does not permit either escape and allows both quote characters to appear unescaped.

▾ Example

Code:

v, mb, t, err := strconv.UnquoteChar(`\"Fran & Freddie's Diner\"`, '"')
if err != nil {
    log.Fatal(err)
}

fmt.Println("value:", string(v))
fmt.Println("multibyte:", mb)
fmt.Println("tail:", t)

Output:

value: "
multibyte: false
tail: Fran & Freddie's Diner\"

type NumError

A NumError records a failed conversion. 

type NumError struct {
    Func string // the failing function (ParseBool, ParseInt, ParseUint, ParseFloat)
    Num  string // the input
    Err  error  // the reason the conversion failed (ErrRange, ErrSyntax)
}

▾ Example

Code:

str := "Not a number"
if _, err := strconv.ParseFloat(str, 64); err != nil {
    e := err.(*strconv.NumError)
    fmt.Println("Func:", e.Func)
    fmt.Println("Num:", e.Num)
    fmt.Println("Err:", e.Err)
    fmt.Println(err)
}

Output:

Func: ParseFloat
Num: Not a number
Err: invalid syntax
strconv.ParseFloat: parsing "Not a number": invalid syntax

func (*NumError) Error 

func (e *NumError) Error() string