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digitalmars.D.learn - char* to long

reply "Mars" <- -.-> writes:
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) );

to go? Or is there something better? Mars
Jan 24 2012
next sibling parent Mantis <mail.mantis.88 gmail.com> writes:
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) );

Or is there something better? Mars

char[] c = "123\0".dup; auto l = parse!long(c); writeln( l );
Jan 24 2012
prev sibling next sibling parent reply "Jonathan M Davis" <jmdavisProg gmx.com> writes:
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 std.conv.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
Jan 24 2012
parent mta`chrono <chrono mta-international.net> writes:
Why not just go the "good old" way? you char* should be zero terminated
when coming from c.

====
private import  core.stdc.stdlib,
                std.stdio;

void main()
{
    const(char)* str = "1234567890".ptr;
    long lng = atoll(str);
    writeln(lng);
}
====
Jan 24 2012
prev sibling parent "Mars" <- -.-> writes:
Thanks for the replies, everyone.I guess I'll go with the double 
conversion for now.
Jan 25 2012