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stdin/stdout

I was attempting to compile the latest version of flex, 2.5.31, when it failed with three errors. All three had to do with invalid lvalues so I opened up filter.c (the offending file) and checked the lines. They were of the form:
if ((stdin = fdopen(0, "r") == NULL)

Since I had just successfully compiled this version on linux, I decided to open /usr/include/stdio.h to see just how stdin and stdout were defined. Here is what I found:
#define stdin (&__sF[0])
#define stdout (&__sF[1])
#define stderr (&__sF[2])

I checked the stdio.h file on the linux computer to see what it contained. It had:
extern FILE *stdin; /* Standard input stream. */
extern FILE *stdout; /* Standard output stream. */
extern FILE *stderr; /* Standard error output stream. */
#ifdef __STDC__
/* C89/C99 say they're macros. Make them happy. */
#define stdin stdin
#define stdout stdout
#define stderr stderr
#endif

I suspected that changing stdin/stdout in the lines that were failing to fp = fdopen... where fp was a FILE* and then adding an else clause of memcpy(stdin, fp, sizeof(FILE)) would be a bad idea but I went ahead and tried it. 5 tests failed when I ran make check (and then 4 subsequent times...) so I don't know if the problem is unrelated or if I was correct and that really was a bad idea.

After all that background, I suppose my questions are:
1) Is there a reason to make stdin, stdout, and stderr be addresses of a FILE rather than a FILE*?
2) How should I hack around the assignment to stdin/stdout?

Thanks,

Steve Checkoway
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