Re: C++: Missing documentation for MODOP_EXPR

[Mark Mitchell <mark at codesourcery dot com>]

On Fri, 2003-08-15 at 11:24, Gabriel Dos Reis wrote:
> Mark Mitchell <mark@codesourcery.com> writes:
> 
> | On Fri, 2003-08-15 at 11:10, Gabriel Dos Reis wrote:
> | > Mark,
> | > 
> | >   While working on the new C++ pretty-printer, I came to realize that 
> | > MODOP_EXPR is documented nowhere.  The only comment I can find is this:
> | > 
> | > /* A whole bunch of tree codes for the initial, superficial parsing of
> | >    templates.  */
> | > 
> | > from cp/cp-tree.def.  While the meaning of most of those "bunch of
> | > tree codes" may be infered from their names and some familiarity with
> | > the C++ front end, that of MODOP_EXPR remains obscure to me.
> | > 
> | > Could you enlighten me?
> | 
> | It's an assignment operator (including compound assignments) while
> | parsing a template.
> 
> I guessed that while looking at some output.  But I could not go far.
> For example, given the following from libstdc++-v3
> 
> 
>     // Convert numeric value of type _Tv to string and return length of
>     // string.  If snprintf is available use it, otherwise fall back to
>     // the unsafe sprintf which, in general, can be dangerous and should
>     // be avoided.
>     template<typename _Tv>
>       int
>       __convert_from_v(char* __out, const int __size, const char* __fmt,
>   #if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
>                        _Tv __v, const __c_locale& __cloc, int __prec = -1)
>       {
>         __c_locale __old = __gnu_cxx::__uselocale(__cloc);
>   #else
>                        _Tv __v, const __c_locale&, int __prec = -1)
>       {
>         char* __old = setlocale(LC_ALL, NULL);
>         char* __sav = static_cast<char*>(malloc(strlen(__old) + 1));
>         if (__sav)
>           strcpy(__sav, __old);
>         setlocale(LC_ALL, "C");
>   #endif
> 
>         int __ret;
>   #ifdef _GLIBCPP_USE_C99
>         if (__prec >= 0)
>           __ret = snprintf(__out, __size, __fmt, __prec, __v);
>         else
>           __ret = snprintf(__out, __size, __fmt, __v);
>   #else
>         if (__prec >= 0)
>           __ret = sprintf(__out, __fmt, __prec, __v);
>         else
>           __ret = sprintf(__out, __fmt, __v);
>   #endif
> 
>   #if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
>         __gnu_cxx::__uselocale(__old);
>   #else
>         setlocale(LC_ALL, __sav);
>         free(__sav);
>   #endif
>         return __ret;
>       }
>   }
> 
> 
> Both 
>           __ret = sprintf(__out, __fmt, __prec, __v);
> and
>           __ret = sprintf(__out, __fmt, __v);
> 
> are represented as MODOP_EXPR.
> 
> My questions are:
> 
>   1) is __ret the first operand?
>   2) is sprintf the second operand?
>   3) is the argument list the third operand?
> 
> I don't think the answers for the last two questions are "yes".  What
> I'm after is the meaning of the tree operands.

The first operand is __ret; the third is the call to sprintf.

The second indicates whether it's a plain assignment operator or a
compound assignment.

-- 
Mark Mitchell <mark@codesourcery.com>
CodeSourcery, LLC