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.
but I want to avoid GC entirely.
The ideal scenario is to have something like "void RenderText(
/*etc*/, const char* fmt, ... )" but I can't seem to figure a
way to pass the variadic parameters to sprintf.
Any ideas?
With sformat, something like this (not tested):
import std.format;
char buf[1024];
auto fmt = sformat(buf, "Foo: %s", 42);
if(fmt.length < buf.length) buf[fmt.length] = 0;
else buf[$-1] = 0;
RenderText(blah, blah, buf.ptr);
sformat returns a slice of the buffer containing the formatted
string. You can use its length to guarantee the buffer is null
terminated.
