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digitalmars.D.learn - int to char at compile time

reply Hendrik Renken <funsheep gmx.net> writes:
hello,

i am trying something like that:

char[] foo(int level, char[] msg)
{
     static c = toString(level);
     return "writefln(\"%d: %s\""~ c ~", \"" ~ msg ~ "\");";
}


int main(char[][] args)
{
    mixin(foo(100, "Test"));
    return 1;
}

but gdmd complaints that toString() cannot be evaluated at compile time. 
is there a way to convert the int to char at compile time?

regards,
Hendrik
Mar 20 2007
next sibling parent reply BCS <ao pathlink.com> writes:
Reply to Hendrik,


 hello,
 
 i am trying something like that:
 
 char[] foo(int level, char[] msg)
 {
 static c = toString(level);
 return "writefln(\"%d: %s\""~ c ~", \"" ~ msg ~ "\");";
 }
 int main(char[][] args)
 {
 mixin(foo(100, "Test"));
 return 1;
 }
 but gdmd complaints that toString() cannot be evaluated at compile
 time. is there a way to convert the int to char at compile time?
 
 regards,
 Hendrik




Don Clugston's decimaldigit and itoa, see
http://trac.dsource.org/projects/ddl/browser/trunk/meta/conv.d

template decimalDigit(int n)
{
  const char[] decimalDigit = "0123456789"[n..n+1];
} 

template itoa(long n)
{   
  static if (n < 0)
     const char[] itoa = "-" ~ itoa!(-n);  
  else static if (n < 10)
     const char[] itoa = decimalDigit!(n); 
  else
     const char[] itoa = itoa!(n/10L) ~ decimalDigit!(n%10L); 
}
Mar 20 2007
parent reply Hendrik Renken <funsheep gmx.net> writes:
BCS wrote:

 Reply to Hendrik,
 

 hello,

 i am trying something like that:

 char[] foo(int level, char[] msg)
 {
 static c = toString(level);
 return "writefln(\"%d: %s\""~ c ~", \"" ~ msg ~ "\");";
 }
 int main(char[][] args)
 {
 mixin(foo(100, "Test"));
 return 1;
 }
 but gdmd complaints that toString() cannot be evaluated at compile
 time. is there a way to convert the int to char at compile time?



 
 Don Clugston's decimaldigit and itoa, see 
 http://trac.dsource.org/projects/ddl/browser/trunk/meta/conv.d




this doesn't work for variables like "level", just with directly wrote 
numbers.

char[] foo(int level, char[] msg)
{
     char[] c = itoa!(level); //does not work
     char[] c = itoa!(100);   //does work
}

is there no chance, to get this variable value converted?
Mar 20 2007
parent Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:
Hendrik Renken wrote:

 BCS wrote:

 Reply to Hendrik,


 i am trying something like that:

 char[] foo(int level, char[] msg)
 {
 static c = toString(level);









You can't make it static, since parameters aren't known when the 
function is compiled. Remember the function is also compiled for regular 
run-time use. It needs to make sense as such.
Also, std.string.toString(int) unfortunately isn't compile-time executable.


 return "writefln(\"%d: %s\""~ c ~", \"" ~ msg ~ "\");";
 }
 int main(char[][] args)
 {
 mixin(foo(100, "Test"));
 return 1;
 }
 but gdmd complaints that toString() cannot be evaluated at compile
 time. is there a way to convert the int to char at compile time?









Yes, see below


 Don Clugston's decimaldigit and itoa, see 
 http://trac.dsource.org/projects/ddl/browser/trunk/meta/conv.d






Doesn't work for CTFE parameters.


 this doesn't work for variables like "level", just with directly wrote 
 numbers.
 
 char[] foo(int level, char[] msg)
 {
     char[] c = itoa!(level); //does not work
     char[] c = itoa!(100);   //does work
 }
 
 is there no chance, to get this variable value converted?



---
import std.stdio;

char[] ctfe_itoa(int value) {
	if (value < 0) return "-" ~ ctfe_itoa(-value);
	if (value < 10) return "0123456789"[value .. value+1];
	return ctfe_itoa(value / 10) ~ ctfe_itoa(value % 10);
}

char[] foo(int level, char[] msg)
{
     auto c = ctfe_itoa(level);
     return "writefln(\"%d: %s\","~ c ~", \"" ~ msg ~ "\");";
}

int main(char[][] args)
{
    pragma(msg, foo(42u, "The answer"));
    pragma(msg, foo(int.max, "int.max"));
    mixin(foo(100, "Test"));
    return 1;
}
---

I originally wrote that function to be more efficient (so it could also 
reasonably be used at runtime) by using a stack-based buffer and 
returning buffer.dup, without any recursion. Unfortunately CTFE didn't 
like it :(.
This version will of course still work at runtime, but will perform way 
too many allocations for a function like this. (I'm not sure if this 
will be a problem at compile time).
Mar 20 2007
prev sibling parent reply torhu <fake address.dude> writes:
Hendrik Renken wrote:


 but gdmd complaints that toString() cannot be evaluated at compile time. 
 is there a way to convert the int to char at compile time?




std.metastrings has a couple of ways of doing this.
Mar 20 2007
parent reply Hendrik Renken <funsheep gmx.net> writes:
torhu wrote:

 Hendrik Renken wrote:
 

 but gdmd complaints that toString() cannot be evaluated at compile 
 time. is there a way to convert the int to char at compile time?



 
 std.metastrings has a couple of ways of doing this.



just for the records: with std.metastrings i am running in the same 
problems having with DDL.

the ctfe_itoa function from Frits van Bommel works great. Thanks again.


another little problem/maybe-bug i ran into:
since i currently only have defined int values for "level", i use a 
switch-Statement to get propper String representations.

const int CORE = 100;

char[] foo(int level, char[] msg)
{
     char[] name;
     switch(level)
     {
	case CORE:
		name = "CORE"; /******* important line ********/

		break;
	default:
		name = "TEST";
	}
     return "writefln(\"%s: %s\", "~ name ~", \"" ~ msg ~ "\");";
}


int main(char[][] args)
{
    mixin(foo(CORE, "Testmsg"));
    return 1;
}


using
name = "CORE";
writes to the console

100: Testmsg


using
name = "\"CORE\"";
gives me what i want

CORE: Testmsg

shouldnt it also work with "CORE"? or am i missing something here?

regards
Hendrik
Mar 21 2007
parent Hendrik Renken <funsheep gmx.net> writes:
--------8< snip code 8<----------

 
 using
 name = "CORE";
 writes to the console
 
 100: Testmsg
 
 
 using
 name = "\"CORE\"";
 gives me what i want
 
 CORE: Testmsg
 
 shouldnt it also work with "CORE"? or am i missing something here?



sorry for bothering, answered the question myself.

Code:
"writefln(\"%s: %s\", "~ name ~", \"" ~ msg ~ "\");"


using name = "CORE";
gives us the line
"writefln(\"%s: %s\", CORE, "Testmsg");"

note: around ~msg~ i inserted " with \"

so this is not "CORE", instead is uses the defined int variable, which 
has (of course) the value 100. giving

100: Testmsg
Mar 21 2007