Darren New <dne### [at] sanrrcom> wrote:

> I saw a bit of a note describing how to use an "assert" and a "check" 
> call in some C++.  "Assert" would exit the program if it failed, and 
> "check" would let the program continue after logging in order to look 
> for more failures.

> But the invocation was along the lines of

> assert(x < 10) <<
>     "The value x is " << x << " but that's too small";

  That's a rather obscure, although clever way of printing error information
in case of assertion failure.

  It's actually not obvious how it's implemented, but at least this would
work:

//------------------------------------------------------------------------
#include <iostream>
#include <cstdlib>

class DataOutput
{
    const bool doExit;

 public:
    DataOutput(bool e): doExit(e) {}

    ~DataOutput()
    {
        if(doExit)
        {
            std::cerr << std::endl;
            std::exit(1);
        }
    }

    template<typename T>
    DataOutput& operator<<(const T& data)
    {
        if(doExit) std::cerr << data;
        return *this;
    }
};

#define assert(cond) ((!(cond)) ? \
  (DataOutput(true) << __FILE__ << " " << __LINE__ \
                    << ": Assertion (" << #cond << ") failed. ") : \
   DataOutput(false))
//------------------------------------------------------------------------

  The only problem I see with this is that you can't compile this in a
way that completely drops out the operator<< calls and its parameters.
The operator<< calls are *always* performed, even if no assertion failure
happens, and there's no way of compiling the program so that the compiler
would drop those calls.

-- 
                                                          - Warp

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