Convert string to integer type in Go

Question

I m trying to convert a string returned from flag Arg n  to an int  What is the idiomatic way to do this in Go

User · Answer

Converting Simple strings

The easiest way is to use the strconv.Atoi() function.

Note that there are many other ways. For example fmt.Sscan() and strconv.ParseInt() which give greater flexibility as you can specify the base and bitsize for example. Also as noted in the documentation of strconv.Atoi():

Atoi is equivalent to ParseInt(s, 10, 0), converted to type int.

Here's an example using the mentioned functions (try it on the Go Playground):

flag.Parse()
s := flag.Arg(0)

if i, err := strconv.Atoi(s); err == nil {
    fmt.Printf("i=%d, type: %T\n", i, i)
}

if i, err := strconv.ParseInt(s, 10, 64); err == nil {
    fmt.Printf("i=%d, type: %T\n", i, i)
}

var i int
if _, err := fmt.Sscan(s, &i); err == nil {
    fmt.Printf("i=%d, type: %T\n", i, i)
}

Output (if called with argument "123"):

i=123, type: int
i=123, type: int64
i=123, type: int

Parsing Custom strings

There is also a handy fmt.Sscanf() which gives even greater flexibility as with the format string you can specify the number format (like width, base etc.) along with additional extra characters in the input string.

This is great for parsing custom strings holding a number. For example if your input is provided in a form of "id:00123" where you have a prefix "id:" and the number is fixed 5 digits, padded with zeros if shorter, this is very easily parsable like this:

s := "id:00123"

var i int
if _, err := fmt.Sscanf(s, "id:%5d", &i); err == nil {
    fmt.Println(i) // Outputs 123
}

User · Answer

For example   package main  import        flag       fmt       os       strconv     func main         flag Parse       s    flag Arg 0         string to int     i  err    strconv Atoi s      if err    nil              handle error         fmt Println err          os Exit 2            fmt Println s  i

User · Answer

Try this import   quot strconv quot    value     quot 123 quot  number err    strconv ParseUint value  10  32  finalIntNum    int number    Convert uint64 To int

User · Answer

Here are three ways to parse strings into integers  from fastest runtime to slowest    strconv ParseInt      fastest strconv Atoi      still very fast fmt Sscanf      not terribly fast but most flexible   Here s a benchmark that shows usage and example timing for each function   package main  import  fmt  import  strconv  import  testing   var num   123456 var numstr    123456   func BenchmarkStrconvParseInt b  testing B      num64    int64 num    for i    0  i  lt  b N  i         x  err    strconv ParseInt numstr  10  64      if x    num64    err    nil         b Error err               func BenchmarkAtoi b  testing B      for i    0  i  lt  b N  i         x  err    strconv Atoi numstr      if x    num    err    nil         b Error err               func BenchmarkFmtSscan b  testing B      for i    0  i  lt  b N  i         var x int     n  err    fmt Sscanf numstr    d    amp x      if n    1    x    num    err    nil         b Error err                You can run it by saving as atoi test go and running go test -bench   atoi test go   goos  darwin goarch  amd64 BenchmarkStrconvParseInt-8      100000000           17 1 ns op BenchmarkAtoi-8                 100000000           19 4 ns op BenchmarkFmtSscan-8               2000000          693   ns op PASS ok      command-line-arguments  5 797s

User · Answer

If you control the input data  you can use the mini version  package main  import        testing       strconv     func Atoi  s string  int       var           n uint64         i int         v byte              for   i  lt  len s   i             d    s i          if  0   lt   d  amp  amp  d  lt    9                v   d -  0            else if  a   lt   d  amp  amp  d  lt    z                v   d -  a    10           else if  A   lt   d  amp  amp  d  lt    Z                v   d -  A    10           else               n   0  break                           n    uint64 10           n    uint64 v            return int n     func BenchmarkAtoi b  testing B        for i    0  i  lt  b N  i             in    Atoi  9999               in             func BenchmarkStrconvAtoi b  testing B        for i    0  i  lt  b N  i             in       strconv Atoi  9999               in              the fastest option  write your check if necessary   Result    Path gt go test -bench   atoi test go goos  windows goarch  amd64 BenchmarkAtoi-2                 100000000               14 6 ns op BenchmarkStrconvAtoi-2          30000000                51 2 ns op PASS ok      path     3 293s

[string] Convert string to integer type in Go?

Converting Simple strings

Parsing Custom strings

Examples related to string

Examples related to go

Examples related to type-conversion