Distinguish float and integer types from string
Hi,
Recently, I was trying to solve some funny coding challenges
(https://www.techgig.com).
The questions were really simple, but I found it interesting
because the website allows to use D.
One of the task was to take a string from STDIN and detect its
type.
There were a few options: Float, Integer, string and "something
else" (which, I think, doesn't have any sense under the scope of
the task).
Anyway, I was struggling to find a built-in function to
distinguish float and integer types from a string.
I came to the following solution:
```
import std.stdio;
import std.range;
import std.conv;
import std.string;
import std.format;
immutable msg = "This input is of type %s";
void main()
{
string type;
auto data = stdin.byLine.takeOne.front;
if (data.isNumeric) {
type = data.indexOf(".") >= 0 ? "Float" : "Integer";
}
else {
type = "string";
}
writeln(msg.format(type));
}
```
But I think that's ugly. The thing is that in PHP, for example, I
would do that like this:
```
if (is_integer($data)) {
//...do smth
}
else if (is_float($data)) {
//...do smth
}
else {
//...do smth
}
```
I tried to use std.conv.to and std.conv.parse, but found that
they can't really do this. When I call `data.to!int`, the value
of "123.45" will be converted to int!
Is there any built-in way to detect these types?
Thanks!
Re: Distinguish float and integer types from string
On Saturday, 9 March 2019 at 18:11:09 UTC, Jacob Shtokolov wrote:w
One of the task was to take a string from STDIN and detect its
type.
The way I'd do this is a very simple loop:
enum Type { String, Float, Int }
if(str.length && str[0] == '-') {
str = str[1 .. $];
}
Type type = str.length ? Type.Int : Type.String;
foreach(ch; str) {
if(ch == '.' && type = Type.Int)
type = Type.Float;
else if(ch < '0' || ch > '9') {
type = Type.String;
break;
}
}
And if you need to support other details, add them on top of
that. For example, exponents on floats may be a second clause
like how I put negative ahead.
You may also choose to use a regular expression though I think
that is overkill for this.
if (data.isNumeric) {
There are several caveats on that isNumeric function: it sees if
something looks like a D numeric literal, which might not be what
you want. For example, isNumeric("1UL") passes because the U and
L suffixes are allowed in D literals...
But I think that's ugly. The thing is that in PHP, for example,
I would do that like this:
```
if (is_integer($data)) {
Simiarly, this also will not od what you want. is_integer("1")
will return false. "1" is of type string. Those functions check
the dynamic type tag, not the contents of a string.
(actually, you arguably can just always return "string" cuz stdin
is basically just a string or a binary stream anyway :P )
PHP's is_numeric returns true for both integer and floating point
things, similarly to D's...
Re: Distinguish float and integer types from string
On 09/03/2019 19:11, Jacob Shtokolov via Digitalmars-d-learn wrote: The thing is that in PHP, for example, I would do The thing is php needs to be able to "lexify" raw input data at runtime, while in D this is done at compile-time. The ompiler has the lexer to do that. But I agree that, for user input, it would be cool to have such a feature available. However, this would quickly become complex because of (the reciprocal of) localisation, or even personalisation. Eg I like to write decimals like: -1'234'457,098 diniz
Re: Distinguish float and integer types from string
On Saturday, 9 March 2019 at 18:11:09 UTC, Jacob Shtokolov wrote:
Hi,
Recently, I was trying to solve some funny coding challenges
(https://www.techgig.com).
The questions were really simple, but I found it interesting
because the website allows to use D.
One of the task was to take a string from STDIN and detect its
type.
There were a few options: Float, Integer, string and "something
else" (which, I think, doesn't have any sense under the scope
of the task).
Anyway, I was struggling to find a built-in function to
distinguish float and integer types from a string.
I came to the following solution:
```
import std.stdio;
import std.range;
import std.conv;
import std.string;
import std.format;
immutable msg = "This input is of type %s";
void main()
{
string type;
auto data = stdin.byLine.takeOne.front;
if (data.isNumeric) {
type = data.indexOf(".") >= 0 ? "Float" : "Integer";
}
else {
type = "string";
}
writeln(msg.format(type));
}
```
But I think that's ugly. The thing is that in PHP, for example,
I would do that like this:
```
if (is_integer($data)) {
//...do smth
}
else if (is_float($data)) {
//...do smth
}
else {
//...do smth
}
```
I tried to use std.conv.to and std.conv.parse, but found that
they can't really do this. When I call `data.to!int`, the value
of "123.45" will be converted to int!
Is there any built-in way to detect these types?
Thanks!
Unless I'm missing something perhaps two functions like this:
bool isInteger(string value) pure nothrow @safe
{
import std.string : isNumeric;
return (isNumeric(value) && value.count(".") == 0) ? true :
false;
}
bool isDecimal(string value) pure nothrow @safe
{
import std.string : isNumeric;
return (isNumeric(value) && value.count(".") == 1) ? true :
false;
}
Re: Distinguish float and integer types from string
On Saturday, 9 March 2019 at 18:11:09 UTC, Jacob Shtokolov wrote:
I tried to use std.conv.to and std.conv.parse, but found that
they can't really do this. When I call `data.to!int`, the value
of "123.45" will be converted to int!
Are you sure? This here works for me:
import std.stdio;
import std.string;
import std.conv;
void main ()
{
auto s = readln.strip;
try
{
int i = to!int (s);
writefln ("string is an int: %s", i);
}
catch(Exception e)
{
try
{
float f = to!float(s);
writefln ("string is a float: %s", f);
}
catch(Exception e)
{
writefln ("string is an neither an int nor a float:
%s", s);
}
}
}
Re: Distinguish float and integer types from string
On Saturday, 9 March 2019 at 18:11:09 UTC, Jacob Shtokolov wrote:
One of the task was to take a string from STDIN and detect its
type.
There were a few options: Float, Integer, string and "something
else" (which, I think, doesn't have any sense under the scope
of the task).
Another std-based solution I came up with:
bool isInteger(string str)
{
if(str.isNumeric)
{
try { return str.to!long == str.to!real; }
catch(ConvException) { return false; }
}
else return false;
}
I tried to use std.conv.to and std.conv.parse, but found that
they can't really do this. When I call `data.to!int`, the value
of "123.45" will be converted to int!
What compiler version are you using? I on the other hand was
surprised that I needed the try-catch above, after having already
checked isNumeric. The documentation claims that the conversion
to int or long would truncate, but my compiler (v2.084.0) throws
instead.
Re: Distinguish float and integer types from string
On Monday, 11 March 2019 at 15:03:39 UTC, XavierAP wrote: What compiler version are you using? I on the other hand was surprised that I needed the try-catch above, after having already checked isNumeric. The documentation claims that the conversion to int or long would truncate, but my compiler (v2.084.0) throws instead. Of course now I realize that using try-catch I no longer need to check isNumeric... My design didn't use try-catch but I had to add it because std.conv:to behaves differently from the documentation: https://dlang.org/phobos/std_conv.html#to Not sure if I need to update my DMD, or it's the documentation that's out of date, or something else is wrong.
