RE: [Boost-users] lexical_cast causes level 4 warnings w/ VC7.1

From: Sam Partington (sam.partington_at_[hidden])
Date: 2003-11-20 13:53:13

Bruce Johnston <mailto:c_kernel_at_[hidden]> wrote:
> I'm working on a project with strict requirements for the
> build settings,
> including mandatory warning level 4 and "treat warnings as errors". I
> discovered that lexical_cast causes warnings C4127, C4511,
> and C4512 when
> compiling with warning level 4 using VC7.1. Try the following
> code for a
> quick repro:

4511 and 4512 are useless warnings.  They are telling you that the copy
constructor and assignment operator are inaccessible.  Even though you're
not trying to call them.  Take the following code

class noncopyable
{
private:
        noncopyable(const noncopyable&);
        noncopyable& operator=(const noncopyable&);
};

class a_resource : noncopyable
{
// ...
};

// ...

{
        a_resource res;
}

Clearly a_resource is not meant to be copied, the developer has gone to
lengths to make that clear.  Indeed it never is copied, or assigned, yet the
warnings will still be issued.  

C4127 is also awkward.  As it gives warnings for some common idioms.  It
refers to conditional expressions being constant.  So :

do { XXX } while(0);

Gives the warning, which is a common implementation of an ASSERT() macro,
and likewise

// in an header :

const bool debug = false;

// in code :

if (debug)
{
}

does also.  None of these technigues indicate a possible error in code.
Ideally all three of these warnings would be disabled in config.hpp.

> As an aside, what warning level is typically used by
> developers working on
> Boost?

On VC6 we build on warning level 3, 4 is just too noisy with the built in
headers.

On VC7.1 we use level 4, but with C4127, C4511, C4512 switched off.

HTH 

Sam

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