Parse string to int golang

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Parse string to int golang

Golang has an inbuilt package called strconv that provide functions that convert string to int. The Atoi() Sscanf(), and ParseInt() are three functions that convert Golang string to int. Go is the statically typed language, data types are bound to variables rather than its values. What does that mean is that if you define the variable as int, it can only be int; you can't assign the string to it without converting the string data type of a variable.How To Convert Golang String To IntGo is statically typed. Every variable has the static type, that is, precisely one type known and fixed at compile time: int, float32, *MyType, []byte, and so on. In Go, data types are used to distinguish one specific type of data, defining the values that you can assign to a type and the operations you can execute on it. In programming, there are times when you will need to convert values between types to modify values differently. So, type conversion in Golang is one of the most important topics.There are three ways you can convert go string to integer(number).Convert string to int with strconv.Atoi(str)Golang strconv.Atoi() function returns its value of type int. If the str is a valid input, then the function returns the equivalent integer number for the passed string number. Atoi stands for ASCII to integer.If no valid conversion takes place, then the function returns zero.See the following code.// hello.go package main import ( "fmt" "strconv" ) func main() { data := "11" if sv, err := strconv.Atoi(data); err == nil { fmt.Printf("%T, %v", sv, sv) } } Outputgo run hello.go int, 11We have defined a string called "11" and use Atoi() function to convert string to an integer.Then we have used the fmt verbs to print the converted data type and value.From the above example, we can see that it convert string "11" to integer 11.In the above code example, we have taken an integer 11 and make it string by putting " ", so after converting to an integer, it will be like 11, which is an ordinary integer, but let's try to convert "Golang" string and see the output.// hello.go package main import ( "fmt" "strconv" ) func main() { data := "Golang" sv, err := strconv.Atoi(data) if err == nil { fmt.Printf("%T, %v", sv, sv) } else { fmt.Println(err) } } In the above code, our data is "Golang," which is a string.Now, strconv.Atoi() function will return an error because the "Golang" string will be counted as invalid syntax and throws an error like the following.strconv.Atoi: parsing "Golang": invalid syntaxOutputgo run hello.go strconv.Atoi: parsing "Golang": invalid syntaxYou can use strconv.Atoi(s) to convert a string s to a 32-bit integer. Atoi() function is equivalent to ParseInt(s, 10, 0) function, converted to type int.Parsing a Custom string to int in GolangThere is also Golang fmt.Sscanf(), which gives even greater flexibility as with a format string, you can specify the number format (like width, base, etc.) along with some additional extra characters in the input string. Let's deep dive into Golang fmt.Sscanf() function.func Sscanf()Golang Sscanf() function scans the argument string, storing successive space-separated values into successive arguments as defined by the format. The Sscanf() returns the number of items successfully parsed. The newlines in the input must match newlines in the format.See the following code example.// hello.go package main import ( "fmt" ) func main() { s := "id:00211" var i int if _, err := fmt.Sscanf(s, "id:%5d", &i); err == nil { fmt.Println(i) } } Outputgo run hello.go 211Here our input is provided in the form of "id:00211" where you have the prefix "id:" and the number is fixed 5 digits, padded with zeros if shorter, this is very quickly parsable. That is why we got 211 in the output.With this Sscanf() method, we must specify the format string to guide the parsing of the values. We can use the standard format codes in the format string. Sscanf works the same way as Sscan, except we must pass a format string as the second argument.Convert string to int using strconv.ParseInt()Golang ParseInt() method interprets the string s in the given base (0, 2 to 36) and bit size (0 to 64) and returns a corresponding value i. See the following syntax.func ParseInt(s string, base int, bitSize int) (i int64, err error)If the base == 0, the base is implied by a string's prefix: base 2 for "0b", base 8 for "0" or "0o", base 16 for "0x", and base 10 otherwise.Also, for the base == 0 only, underscore characters are allowed per the Go integer literal syntax. If the base is below 0, is 1, or is above 36, an error is returned.The bitSize argument defines an integer type that the result must fit into. The Bit sizes 0, 8, 16, 32, and 64 correspond to int, int8, int16, int32, and int64. If bitSize is below 0 or above 64, an error will be thrown.The errors that ParseInt returns have particular type *NumError and include err.Num = s. If the 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 the signed integer of the given size, err.Err = ErrRange and the returned value is the maximum magnitude integer of the appropriate bitSize and sign.See the following code example.// hello.go package main import ( "fmt" "reflect" "strconv" ) func main() { fmt.Println("Convert String into Integer Data type") str3 := "AppDividend" fmt.Println("Before String Value: ", str3) fmt.Println("Before converting Datatype:", reflect.TypeOf(str3)) intStr, _ := strconv.ParseInt(str3, 10, 64) fmt.Println("After Integer Value: ", intStr) fmt.Println("After converting Datatype:", reflect.TypeOf(intStr)) } Outputgo run hello.go Convert String into Integer Data type Before String Value: AppDividend Before converting Datatype: string After Integer Value: 0 After converting Datatype: int64Here, we get output 0 because the string is built upon characters and not signed integers, but its data type is changed from string to int64. We have used Golang ParseInt() function to convert string to an integer. We have used the reflection to get the datatype of the variables using reflect.TypeOf() function.Reflection in computing is the capacity of the program to study its structure, especially through types; it's a form of metaprogramming. The reflection forms on the type system.func TypeOf(i interface{}) TypeThe TypeOf() returns a reflection Type that represents the dynamic type of i. If i is the nil interface value, TypeOf returns nil.Let's take another example. See the below code.// hello.go package main import ( "fmt" "reflect" "strconv" ) func main() { fmt.Println("Convert String into Integer Data type") str3 := "11192146" fmt.Println("Before String Value: ", str3) fmt.Println("Before converting Datatype:", reflect.TypeOf(str3)) intStr, _ := strconv.ParseInt(str3, 10, 64) fmt.Println("After Integer Value: ", intStr) fmt.Println("After converting Datatype:", reflect.TypeOf(intStr)) } Outputgo run hello.go Convert String into Integer Data type Before String Value: 11192146 Before converting Datatype: string After Integer Value: 11192146 After converting Datatype: int64ConclusionGolang string is the sequence of one or more characters (letters, numbers, or symbols). Strings are the most used form of data in computer programs, and you may need to convert the strings to numbers or numbers to strings reasonably often, especially when you are taking in user-generated data.Strings can be converted to numbers by using a Golang inbuilt strconv package in the Go standard library. The strconv package has functions for converting both integer and float number types. This is a pervasive operation when accepting input from the user.We have seen three methods that can convert Go string to int.If your string does not have decimal places, you'll most likely want to convert it to an integer by using the strconv.Atoi function. But you can always go for Sscanf() function for complex scenarios.Finally, How To Convert Golang String To Number Example Tutorial is over. Golang strconv.ParseInt() is an inbuilt function that parses a decimal string (base 10) and checks if it fits into an int64. The size of an int is implementation-specific, it's either 32 or 64 bits, and that is why you won't lose any key info when converting from int to int64.Golang string to int64Go strconv.ParseInt to convert a decimal string (base 10) and check that it fits into a 64-bit signed integer.func ParseInt()ParseInt interprets the string in the given base (0, 2 to 36) and bit size (0 to 64) and returns the corresponding value i. If a base argument is 0, the true base is implied by a string's prefix: 2 for "0b", 8 for "0" or "0o", 16 for "0x", and 10 otherwise. Also, for argument base 0 only, underscore characters are permitted as defined by the Golang syntax for integer literals. The bitSize parameter specifies an integer type that the result must fit into. Bit sizes 0, 8, 16, 32, and 64 correspond to int, int8, int16, int32, and int64. If the bitSize is below 0 or above 64, an error is returned.Let's use the Golang strconv.ParseInt() function to convert string to int64 in Golang.// hello.go package main import ( "fmt" "strconv" ) func main() { str := "101" n, err := strconv.ParseInt(str, 10, 64) if err == nil { fmt.Printf("%d of type %T", n, n) } } Outputgo run hello.go 101 of type int64The two numeric arguments represent the base (0, 2 to 36) and a bit size (0 to 64).If the first argument is 0, the base is implied by a string's prefix: base 16 for "0x", base 8 for "0", and base 10 otherwise.The second argument describes an integer type that a result must fit into. Bit sizes 0, 8, 16, 32, and 64 correspond to int, int8, int16, int32, and int64.Example 2: Convert Golang string to intSee the following code.// hello.go package main import ( "fmt" "strconv" ) func main() { v32 := "-354634382" if s, err := strconv.ParseInt(v32, 10, 32); err == nil { fmt.Printf("%T, %v", s, s) } if s, err := strconv.ParseInt(v32, 16, 32); err == nil { fmt.Printf("%T, %v", s, s) } v64 := "-3546343826724305832" if s, err := strconv.ParseInt(v64, 10, 64); err == nil { fmt.Printf("%T, %v", s, s) } if s, err := strconv.ParseInt(v64, 16, 64); err == nil { fmt.Printf("%T, %v", s, s) } } Outputgo run hello.go int64, -354634382 int64, -3546343826724305832Parsing string into int64See the following code.// hello.go package main import ( "fmt" "reflect" "strconv" ) func main() { var s string = "112119462926854775" i, err := strconv.ParseInt(s, 10, 64) if err != nil { panic(err) } fmt.Printf("Bonjour, %v with type %s!", i, reflect.TypeOf(i)) }Outputgo run hello.go Bonjour, 112119462926854775 with type int64!ConclusionIf you want to convert Golang string to int64, you should also pass in the 64 as the last argument to ParseInt(), or it might not produce the expected value on the 32-bit system.See also Go (Golang) offers a vast standard library with a lot tools coming directly out of the box for most every day tasks. One of this is the conversion of strings to numeric values. For this kind of problem we have an handful of different options, here some of them: Use strconv.ParseInt One option is strconv.ParseInt. Which gives you a lot of flexibility on what numeric base (base 2, 10, 16 etc) the expected integer is supposed to be and the bitsize (16, 32, 64 etc) of the integer you are trying to parse. func ParseInt(s string, base int, bitSize int) (int64, error) ParseInt interprets a string s in the given base (0, 2 to 36) and bit size (0 to 64) and returns the corresponding value i. If the base argument is 0, the true base is implied by the string's prefix: 2 for "0b", 8 for "0" or "0o", 16 for "0x", and 10 otherwise. Also, for argument base 0 only, underscore characters are permitted as defined by the Go syntax for integer literals. 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. If bitSize is below 0 or above 64, an error is returned. 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. Here's an example below package main import ( "strconv" "log" ) func main() { i, err := strconv.ParseInt("12345", 10, 64) if err != nil { log.Fatal(err) } log.Println(i) } This is the expected output 2009/11/10 23:00:00 12345 Use strconv.Atoi One options is to use strconv.Atoi function which is much quicker to use as it's using by default a decimal base. func Atoi(s string) (int, error) Atoi is equivalent to ParseInt(s, 10, 0), converted to type int. Here's an example below package main import ( "strconv" "log" ) func main() { i, err := strconv.Atoi("12345") if err != nil { log.Fatal(err) } log.Println(i) } This is the expected output for the much simpler strconv.Atoi function 2009/11/10 23:00:00 12345 Use fmt.Sscanf One more sophisticated option is to use the fmt.Sscanf function. Which allows you to parse integer values inside strings but using different format options func Sscanf(str string, format string, a ...interface{}) (n int, err error) Sscanf scans the argument string, storing successive space-separated values into successive arguments as determined by the format. It returns the number of items successfully parsed. Newlines in the input must match newlines in the format. Let's see an example to better understand its possible use cases package main import ( "fmt" ) func main() { var userID, sessionID int _, err := fmt.Sscanf("UserID:12345 SessionID:54321", "UserID:%d SessionID:%d", &userID, &sessionID) if err != nil { panic(err) } fmt.Printf("%d, %d", userID, sessionID) } Here's an example of the output for this code snippet 12345, 54321 Ready for your next Go Job? Submit your profile and get hired on Golang Cafe Numeric Conversions String Conversions 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 := strconv.Quote("Hello, ") q := strconv.QuoteToASCII("Hello, ") QuoteRune and QuoteRuneToASCII are similar but accept runes and return quoted Go rune literals. Unquote and UnquoteChar unquote Go string and rune literals. 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 FormatComplex(c complex128, fmt byte, prec, bitSize int) 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 ParseComplex(s string, bitSize int) (complex128, 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 func (e *NumError) Unwrap() error View Source const IntSize = intSize IntSize is the size in bits of an int or uint value. View Source var ErrRange = errors.New("value out of range") ErrRange indicates that a value is out of range for the target type. View Source var ErrSyntax = errors.New("invalid syntax") ErrSyntax indicates that a value does not have the right syntax for the target type. 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. package main import ( "fmt" "strconv" ) func main() { b := []byte("bool:") b = strconv.AppendBool(b, true) fmt.Println(string(b)) } Output: bool:true 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. package main import ( "fmt" "strconv" ) func main() { 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(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. package main import ( "fmt" "strconv" ) func main() { 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(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. package main import ( "fmt" "strconv" ) func main() { b := []byte("quote:") b = strconv.AppendQuote(b, `"Fran & Freddie's Diner"`) fmt.Println(string(b)) } Output: quote:"\"Fran & Freddie's Diner\"" 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. package main import ( "fmt" "strconv" ) func main() { b := []byte("rune:") b = strconv.AppendQuoteRune(b, '') fmt.Println(string(b)) } Output: rune:'' 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. package main import ( "fmt" "strconv" ) func main() { b := []byte("rune (ascii):") b = strconv.AppendQuoteRuneToASCII(b, '') fmt.Println(string(b)) } Output: rune (ascii):'\u263a' 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(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. package main import ( "fmt" "strconv" ) func main() { 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(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(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. package main import ( "fmt" "strconv" ) func main() { 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(s string) (int, error) Atoi is equivalent to ParseInt(s, 10, 0), converted to type int. package main import ( "fmt" "strconv" ) func main() { v := "10" if s, err := strconv.Atoi(v); err == nil { fmt.Printf("%T, %v", s, s) } } Output: int, 10 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. package main import ( "fmt" "strconv" ) func main() { fmt.Println(strconv.CanBackquote("Fran & Freddie's Diner ")) fmt.Println(strconv.CanBackquote("`can't backquote this`")) } Output: true false func FormatBool(b bool) string FormatBool returns "true" or "false" according to the value of b. package main import ( "fmt" "strconv" ) func main() { v := true s := strconv.FormatBool(v) fmt.Printf("%T, %v", s, s) } Output: string, true func FormatComplex(c complex128, fmt byte, prec, bitSize int) string FormatComplex converts the complex number c to a string of the form (a+bi) where a and b are the real and imaginary parts, formatted according to the format fmt and precision prec. The format fmt and precision prec have the same meaning as in FormatFloat. It rounds the result assuming that the original was obtained from a complex value of bitSize bits, which must be 64 for complex64 and 128 for complex128. 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), 'G' ('E' for large exponents, 'f' otherwise), 'x' (-0xd.ddddp?ddd, a hexadecimal fraction and binary exponent), or 'X' (-0Xd.ddddP?ddd, a hexadecimal fraction and binary exponent). The precision prec controls the number of digits (excluding the exponent) printed by the 'e', 'E', 'f', 'g', 'G', 'x', and 'X' formats. For 'e', 'E', 'f', 'x', and 'X', it is the number of digits after the decimal point. For 'g' and 'G' it is the maximum number of significant digits (trailing zeros are removed). The special precision -1 uses the smallest number of digits necessary such that ParseFloat will return f exactly. package main import ( "fmt" "strconv" ) func main() { v := 3.1415926535 s32 := strconv.FormatFloat(v, 'E', -1, 32) fmt.Printf("%T, %v", s32, s32) s64 := strconv.FormatFloat(v, 'E', -1, 64) fmt.Printf("%T, %v", s64, s64) } Output: string, 3.1415927E+00 string, 3.1415926535E+00 func FormatInt(i int64, base int) string FormatInt returns the string representation of i in the given base, for 2

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