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

28 Apr 2010


      On 28 April 2010 11:04, Joseph Gauterin  wrote:
...
...
My point is that difference between binding to echo and echo2 (string
vs. const char*) should not lead do different behavior. Otherwise user
has to be very careful on signature of bind'ed function.
Passing a std::string vs a const char* to boost::bind should have as
close as possible to same behaviour as passing that parameter to a
normal C++ function..
...
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.
That code is safe - the lifetime of string literals is the lifetime of
the program.
Good point! Yes, it's my mistake. I should have write something like that:

void f1(const string& s) {
  cout << s << '\n';
}

function make1(const string& s) {
  return bind(f1, s); //ok, bind copies s
}

void f2(const char* s) { //old-style method. Legacy code we reuse
  cout << s << '\n';
}

function make2(const string& s) {
  return bind(f2, s.c_str()); //ups, bind copies pointer
}

int main() {
  string s("abc");
  function g1 = make1(s);
  function g2 = make2(s);

  s = "xyz";
  g1(); //produces "abc"
  g2(); //produces "xyz"
}
...
Just to be clear, using char*s as strings is tricky and error prone -
but that is a problem with C++, not a problem with boost.
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-- 
Piotr Jachowicz