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

Chandler Carruth chandlerc at google.com
Mon Jun 4 13:44:30 PDT 2012

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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