Re: C++: Missing documentation for MODOP_EXPR

[Gabriel Dos Reis <gdr at integrable-solutions dot net>]

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.

Thanks.

-- Gaby