Lua string to int

Question

How can I convert a string to an integer in Lua   I have a string like this   a    10    I would like it to be converted to 10  the number

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Lua 5 3 1  Copyright  C  1994-2015 Lua org  PUC-Rio  gt  math floor  10    10  gt  tonumber  10    10  gt   10    0  10 0  gt   10    0  10

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local a    10  print type a   local num   tonumber a  print type num     Output     string                                                                                                                                                                              number

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tonumber  e    base    tonumber takes two arguments  first is string which is converted to number and second is base of e   Return value tonumber is in base 10   If no base is provided it converts number to base 10    gt  a    101   gt  tonumber a  101   If base is provided  it converts it to the given base    gt  a    101   gt    gt  tonumber a  2  5  gt  tonumber a  8  65  gt  tonumber a  10  101  gt  tonumber a  16  257  gt     If e contains invalid character then it returns nil    gt  --   Failed because base 2 numbers consist  0 and 1  --    gt  a    112   gt  tonumber a  2  nil  gt    gt  --   similar to above one  this failed because --    gt  --   base 8 consist  0 - 7  --    gt  --   base 10 consist  0 - 9  --    gt  a    AB   gt  tonumber a  8  nil  gt  tonumber a  10  nil  gt  tonumber a  16  171   I answered considering Lua5 3

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here is what you should put  local stringnumber    10  local a   tonumber stringnumber  print a   10   output   20

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All numbers in Lua are floats  edit  Lua 5 2 or less   If you truly want to convert to an  int   or at least replicate this behavior   you can do this   local function ToInteger number      return math floor tonumber number  or error  Could not cast       tostring number        to number      end   In which case you explicitly convert the string  or really  whatever it is  into a number  and then truncate the number like an  int  cast would do in Java    Edit  This still works in Lua 5 3  even thought Lua 5 3 has real integers  as math floor   returns an integer  whereas an operator such as number    1 will still return a float if number is a float

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It should be noted that math floor   always rounds down  and therefore does not yield a sensible result for negative floating point values   For example  -10 4 represented as an integer would usually be either truncated or rounded to -10  Yet the result of math floor   is not the same   math floor -10 4    gt  -11   For truncation with type conversion  the following helper function will work   function tointeger  x       num   tonumber  x       return num  lt  0 and math ceil  num   or math floor  num   end   Reference  http   lua 2524044 n2 nabble com 5-3-Converting-a-floating-point-number-to-integer-td7664081 html

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say the string you want to turn into a number is in the variable S  a tonumber S    provided that there are numbers and only numbers in S it will return a number  but if there are any characters that are not numbers  except periods for floats  it will return nil

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You can force an implicit conversion by using a string in an arithmetic operations as in a   10    0  but this is not quite as clear or as clean as using tonumber explicitly

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I would recomend to check Hyperpolyglot  has an awesome comparison  http   hyperpolyglot org   http   hyperpolyglot org more str-to-num-note  ps  Actually Lua converts into doubles not into ints      The number type represents real  double-precision floating-point    numbers    http   www lua org pil 2 3 html

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The clearer option is to use tonumber   As of 5 3 2  this function will automatically detect  signed  integers  float  if a point is present  and hexadecimal  both integers and floats  if the string starts by  0x  or  0X     The following snippets are shorter but not equivalent     a   0 -- forces the conversion into float  due to how   works   a   0 --    is the bitwise or  forces the conversion into integer   -- However  unlike  math tointeger   it errors if it fails

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Use the tonumber function  As in a   tonumber  10

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Since lua 5 3 there is a new math tointeger function for string to integer  Just for integer  no float  For example  print math tointeger  quot 10 1 quot    -- nil print math tointeger  quot 10 quot    -- 10  If you want to convert integer and float  the tonumber function is more appropriate

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You can make an accessor to keep the  10  as int 10 in it   Example   x   tonumber  10     if you print the x variable  it will output an int 10 and not  10   same like Python process  x   int  10    Thanks

[lua] Lua string to int

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