Re: [Boost-users] [Bind] Unexpected behavior when binding const char* to function

Subject: Re: [Boost-users] [Bind] Unexpected behavior when binding const char* to function
From: Lars Viklund (zao_at_[hidden])
Date: 2010-04-27 17:48:07

On Tue, Apr 27, 2010 at 11:35:19PM +0200, Piotr Jachowicz wrote:
> I've called it "unexpected", because f1() and f2() in code below
> behaves differently:
> 
> void echo1(const char* c) {
>   cout << c << '\n';
> }
> 
> void echo2(const string& s) {
>   cout << s << '\n';
> }
> 
> int main() {
>   boost::function<void ()> f1 = boost::bind(echo1, "abc"); //ups!
> binding to address of temporary
>   boost::function<void ()> f2 = boost::bind(echo2, "abc"); //ok, bind
> copies temporary string("abc")
>   f1(); f2();
> }

First off, your first bind comment is incorrect, as string literals have
static storage duration, and both examples behave as intended.

So, according to you, no-one should ever be able to bind a function
parameter without it magically being cloned, in a way I can't remotely
imagine how to implement.

If a developer does not understand strings, they should learn how to
use strings, not horribly mutilate unrelated APIs.

The bind rules are very simple. It copies whatever arguments you bind to
it, and stores them internally. If you feed it a raw pointer, it copies
the raw pointer value. If you pass it an object, it copies the object.

It's all very simple, and if you want different lifetime semantics for
say pointers, use a smart pointer like shared_ptr.

-- 
Lars Viklund | zao_at_[hidden]