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digitalmars.D.learn - readf

reply Nick Voronin <elfy.nv gmail.com> writes:
Hello.

I'm new to D and I stumbled upon something strange about readf while writing
some test code.

The code:

import std.stream;
import std.stdio;

int main(char[][] args)
{
	string input = "2abc";
	auto memstream = new TArrayStream!(string)(input);
	int x;
	memstream.readf("%d", &x);
	char[] s = memstream.readString(x);
	writefln("%d:%s", x, s); // expected 2:ab, writes 2:bc.
	return 0;
}

After looking in stream.d I can understand why it is working in unexpected way
(readf uses ungetc() which has no effect on readString() ), but is it intended
behavior? I see in documentation that ungetc() affects only what is read
afterwards with getc(), but no mention that readf() is incompatible with other
reading methods.

It wouldn't even be the problem if I knew for sure that there is always
_exactly_ one char offset, or that return value of readf must be number of
bytes read from stream. Is it so or is it all just the way it happened to be in
current implementation?

On another topic. Compiled with D 2.050 it won't work at all, printing
"object.Error: Access Violation". Apparently readf in 2.0 requires mutable
string as a format string. Writing it like this

memstream.readf("%d".dup, &x);

works. Is it intended too?

On yet another topic :) Is there alternative to stream.readf? Somehow while
searching for explanation of unexpected behavior I got the idea that readf and
streams considered to be second-class citizens in world of D and they are not a
proper way to do things, so no one really cares about them... Therefore the
question. What do I use to read numbers from file?
Nov 02 2010
parent bearophile <bearophileHUGS lycos.com> writes:
Nick Voronin:

 On yet another topic :) Is there alternative to stream.readf? Somehow while
searching for explanation of unexpected behavior I got the idea that readf and
streams considered to be second-class citizens in world of D and they are not a
proper way to do things, so no one really cares about them... Therefore the
question. What do I use to read numbers from file?

In std.stdio there is a function to read a line, and then you may use std.conv.parse or std.conv.to. Bye, bearophile
Nov 02 2010