char* to long

Jonathan M Davis jmdavisProg at
Tue Jan 24 13:45:39 PST 2012

On Tuesday, January 24, 2012 23:02:18 Mantis wrote:
> 24.01.2012 22:48, Mars пишет:
> > Hello everybody.
> > I have to convert a char* (from a C function) to long. At the moment
> > I'm using
> > 
> >> long foo = to!long( to!string(bar) );
> > 
> > but this doesn't feel right... with 2 to calls. Is this the way to go?
> > Or is there something better?
> > 
> > Mars
> This seems to work:
> char[] c = "123\0".dup;
> auto l = parse!long(c);
> writeln( l );

Yeah, but note that that's really equivalent to

auto foo = to!long(to!(char[])(bar));

except that you're creating an extra variable and using parse with its 
somewhat different semantics. In either case, you need to convert it from a 
char* to an actual character array of some kind before converting it to a 
long, and that means that you're allocating memory. In general, I would 
recommend just doing what the OP said

auto foo = to!long(to!string(bar));

It's the cleanest solution IMHO, and in general, that extra bit of memory 
allocation isn't a big deal. However, if you know the length of the char*, 
then you can slice it and pass that to e.g.

auto foo = to!long(bar[0 .. 3]);

But you have to know the length of the string already - or use strlen on it to 
get its length. e.g.

auto foo = to!long(bar[0 .. strlen(bar)]);

It's quite doable and probably faster than converting to string and then to 
long, but it's certainly uglier code. This should only be a problem when 
interfacing with C though, since you really shouldn't be using char*'s or 
null-terminated strings otherwise.

- Jonathan M Davis

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