I think your detailed investigation demonstrates why the code I posted in repsonse to creamygoodness's post behaves the way it does.

After much poking and scratching and re-reading of suggestions that have been kindly and thoughtfully presented here, I've eventually come up with using this approach in the PDL code:

#include <stdio.h>

#if defined _MSC_VER && _MSC_VER < 1400
#pragma optimize("", off)
#endif 

int main(void) {

#if defined _MSC_VER && _MSC_VER < 1400
   double nv = 2.0 / 3;
   float foo = 2.0 / 3;
   float dummy = (float)nv;

   if(foo == dummy) printf("True ");
   else printf("False ");

#else
   double nv = 2.0 / 3;
   float foo = 2.0 / 3;

   if(foo == (float)nv) printf("True ");
   else printf("False ");

#endif

   return 0;
}
[download]

It seems to be doing the right thing with all of my compilers.
I don't think that C script needs to have the optimization turned off - the creation of the dummy variable is alone sufficient to get the behaviour I'm after. But for some reason, in the PDL code, creation of the dummy variable is *not*, by itself, sufficient - optimization also needs to be disabled. (I turn it off for the setvaltobad functions, then turn it back on again.)

Thanks to *all* who replied.

Cheers,
Rob

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.