macros with global variables?

["Robert P. J. Day" <rpjday@mindspring.com>]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1310 bytes --]


  not sure if this is outside the scope of this mailing list but i
just downloaded the source for a simple SSL-aware ftp client
(netkit-ftp-ssl), did the configure and the make and got:

ftp.c: In function ârecvrequestâ:
ftp.c:1127: error: âpdataâundeclared (first use in this function)
ftp.c:1127: error: (Each undeclared identifier is reported only once
ftp.c:1127: error: for each function it appears in.)


  ok, fair enough, check the offending header file to find the
following macro definition:

#define is_ssl_fd(X,Y)    ( (SSL_get_fd((X))==0) || \
                            (SSL_get_fd((X))==1) || \
                            (SSL_get_fd((X))==pdata) || \
                            (SSL_get_fd((X))==(Y)) \

  ?????.  so i have a macro which accepts two arguments, but expands
to include an explicit reference to something called "pdata", which
does not exist, hence the error message.

  i tend to avoid defining macros that refer to anything but their own
arguments.  what might the above mean?  is there some well-known idiom
for C programmers that makes the above, in some way, acceptable?
(i've perused the code and the object "pdata", whatever that is, is
simply not defined anywhere.  so is there a context in which the above
makes sense in some way?)

rday