[cfe-commits] [patch] Added a suggestion when a std::string is passed to printf()

Sam Panzer panzer at google.com
Mon Jun 4 14:09:17 PDT 2012

Now I'm wondering how much of this behavior should be "string"-specific. If
we're paying attention to conversion operators from non-POD types, why not
check for all possible conversion operators? I think this is a better
solution than checking to see if there's a conversion operator from the
return type of a c_str() function.

Not depending on std::string was the plan, and in fact how I implemented it

On Mon, Jun 4, 2012 at 1:44 PM, Chandler Carruth <chandlerc at google.com>wrote:

> On Mon, Jun 4, 2012 at 1:37 PM, Sam Panzer <panzer at google.com> wrote:
>> Here is one other question: With this patch, incorrectly passing an
>> std::string to printf generates an error (can't pass non-POD member), a
>> warning (printf format doesn't match), and a note (the c_str() suggestion).
>> Is this the behavior we want?
> I don't think so... Ideally:
> 1) If we are about to issue a an error (non-POD object passed through
> printf), check whether the non-POD object has a 'c_str()' method that
> returns a type which matches the format specifier. If so, use a specific
> diagnostic message for the error, attach a fixit-hint suggesting
> '.c_str()', and continue parsing as-if the user had done that.
> 2) If there is no error (passing a std::string* perhaps), then in the
> warning message, give a more precise message than 'cannot convert
> std::string* to const char*' or whatever by checking if there is a c_str()
> method that matches the type of the printf.
> One thing I would encourage you to do: don't base this on 'std::string'. I
> actually think the error/warning should fire for any class type with a
> c_str method that returns a viable type. That way non-standard string
> libraries will get the same benefit if they conform the the same conceptual
> interface as the standard string library.
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