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

On 27 April 2010 20:55, Michael Caisse wrote:

Piotr -

I don't think this is "unexpected behavior" to most. You have *not* bound abc. You have bound a pointer. What that pointer points to may change and when you use the pointer it may very well point to something different than at the time of the bind.

This isn't "unexpected". Your bind is to a pointer. You need to either ensure that the value pointed at doesn't change or you can pass an object containing the data itself.

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 f1 = boost::bind(echo1, "abc"); //ups! binding to address of temporary boost::function f2 = boost::bind(echo2, "abc"); //ok, bind copies temporary string("abc") f1(); f2(); } Incoming book "How to code with C++0x and not commit suicide" will have to contain advise "When you bind, ensure that function signature have no pointers; otherwise you are in trouble". To be serious: library should naturally promote its proper usage. Code like "boost::bind(echo1, "abc")" looks natural, does not emit any warning, and is dangerous. Cases like that promote stereotype "It's better to avoid Boost because it contains many traps". I think that compiler warning would save hours of debugging for many programmers.

michael

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---------------------------------- Michael Caisse Object Modeling Designs www.objectmodelingdesigns.com

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