Convert a String to int

Question

Note  this question contains deprecated pre-1 0 code  The answer is correct  though   To convert a str to an int in Rust  I can do this   let my int   from str   lt int gt  my str     The only way I know how to convert a String to an int is to get a slice of it and then use from str on it like so   let my int   from str   lt int gt  my string as slice       Is there a way to directly convert a String to an int

User · Answer

Well  no  Why there should be  Just discard the string if you don t need it anymore    amp str is more useful than String when you need to only read a string  because it is only a view into the original piece of data  not its owner  You can pass it around more easily than String  and it is copyable  so it is not consumed by the invoked methods  In this regard it is more general  if you have a String  you can pass it to where an  amp str is expected  but if you have  amp str  you can only pass it to functions expecting String if you make a new allocation   You can find more on the differences between these two and when to use them in the official strings guide

User · Answer

You can use the FromStr trait s from str method  which is implemented for i32   let my num   i32  from str  9   unwrap or 0

User · Answer

With a recent nightly  you can do this   let my int   from str   lt int gt   amp  my string     What s happening here is that String can now be dereferenced into a str   However  the function wants an  amp str  so we have to borrow again   For reference  I believe this particular pattern   amp    is called  cross-borrowing

User · Answer

You can directly convert to an int using the str  parse   lt T gt    method   let my string    27  to string         parse    works with   amp str  and  String   let my int   my string parse   lt i32 gt    unwrap      You can either specify the type to parse to with the turbofish operator     lt  gt   as shown above or via explicit type annotation   let my int  i32   my string parse   unwrap      As mentioned in the comments  parse   returns a Result  This result will be an Err if the string couldn t be parsed as the type specified  for example  the string  peter  can t be parsed as i32

User · Answer

If you get your string from stdin   read line  you have to trim it first   let my num  i32   my num trim   parse       expect  please give me correct string number

User · Answer

So basically you want to convert a String  into an Integer right  here is what I mostly use and that is also mentioned in official documentation    fn main          let char    23       let char   i32   char trim   parse   unwrap        println        char   1        This works for both  String and  amp str  Hope this will help too

User · Answer

let my u8  u8    42  parse   lt u8 gt    unwrap    let my u32  u32    42  parse   lt u32 gt    unwrap        or  to be safe  match the  Err  match  foobar  parse   lt i32 gt        Ok n    gt  do something with n     Err e    gt  weep and moan        str  parse   lt u32 gt  returns a Result lt u32  core  num  ParseIntError gt  and Result  unwrap  Unwraps a result  yielding the content of an Ok  or  panics if the value is an Err  with a panic message provided by the Err s value    str  parse is a generic function  hence the type in angle brackets

[rust] Convert a String to int?

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