Smartest way to read a number?

[Jonathan M Davis]

On Thursday, November 10, 2011 13:48 Fabian wrote:
> Hey guys.
> 
> I just want to write a few console applications. Usualy I have to read
> numbers to calculate some values. But what's the smartest way to read and
> convert the input?
> 
> I've coded these lines:
> 
> import std.stdio, std.string, std.conv;
> 
> T readNumber(T)()
> {
> string buffer;
> stdin.readln(buffer);
> buffer = chomp(buffer);
> 
> if(isNumeric(buffer))
> {
> return parse!T(buffer);
> }
> else
> {
> throw new Exception("Input is not a number!");
> }
> }
> 
> void main()
> {
> try
> {
> int n = readNumber!int();
> writeln(n);
> 
> float f = readNumber!float();
> writeln(f);
> }
> catch(Exception e)
> {
> writeln(e.msg);
> }
> }
> 
> Can I use that function or is there a cleaner way to do this job?

parse already throws an exception if it can't parse anything. There's no need 
to call isNumeric and throw an exception yourself. However, if you want to 
guarantee that the whole string is a valid number instead of just the 
beginning (parse parses as much as it can, leaving what it can't in the 
string, and throwing if it couldn't parse anything), then use std.conv.to. It 
requires that the string be _exactly_ a number (no whitespace or extraneous 
characters). It also doesn't consume the string at all (since it's converting 
all or nothing).

- Jonathan M Davis