Formatting a string on a variadic parameter function without using GC

[Luis via Digitalmars-d-learn]

On Wednesday, 2 March 2016 at 04:12:13 UTC, Mike Parker wrote:
> On Wednesday, 2 March 2016 at 01:39:13 UTC, David G. Maziero 
> wrote:
>
>> Consider the following function:
>>
>> void RenderText( FontBMP font, int x, int y, const char* text )
>> {
>
>> 	for( int r=0; text[r]!='\0'; ++r )
>> 	{
>
> You're asking for trouble here. There's no guarantee that any D 
> string is going to be null terminated. String literals are, but 
> beyond that, all bets are off.
>
>
>>
>> 	char[256] text;
>> 	sprintf( &text[0], "Player: pos:%.3f - speed:%.3f", 
>> player.position, player.speed );
>
> Instead of sprintf, look into using std.format.sformat [1] (see 
> below). It's equivalent to std.format.format, but allows you to 
> provide a buffer.
>
>
>> 	RenderText( font, 0, 0, cast(char*)text );
>
> It's considered bad form to cast an array to a pointer like 
> this. If you need a pointer to an array, just use the ptr 
> property: text.ptr. Always be aware of the null terminator 
> situation, though, when passing to C.
>
>>
>> I could simply do "RenderText(font,0,0,"FPS: 
>> "~to!string(fps));"
>
> Won't compile without using the .ptr property (or casting, 
> which again, you shouldn't do). Moreover, you run into the null 
> terminator problem. "FPS :" will be null terminated because 
> it's a literal, but the string produced by concatentating it 
> with the result of to!string would not be.
>

Read https://dlang.org/spec/arrays.html#strings and try to use 
std.string.toStringz 
(http://dlang.org/phobos/std_string.html#.toStringz)