[Bug-glpk] Minor patch for recent glpk up to version 4.37

[Nelson H. F. Beebe]

Versions 4.35--4.37 of glpk have failed to build on SGI IRIX MIPS, but
I only today had the time to figure out why.

The problem is this definition in the native <ctype.h> file:

    #define _G       0x40000000      /* Graphic characters only */

It conflicts with this piece of code in src/glpnet03.c:

    int glp_netgen(glp_graph *_G, int _v_rhs, int _a_cap, int _a_cost,
          const int parm[1+15])

The rules of ISO Standard C (1989 and 1999) are that names beginning
with two underscores, and names beginning with an underscore and a
capital letter, are reserved for the implementation.  Thus, IRIX is
permitted to define _G as shown above, and glpk is in error in using
that name for its own variables.

As a quick workaround, I made this simple patch to include/glpstd.h:

% diff -c include/glpstd.h.~1~ include/glpstd.h
*** include/glpstd.h.~1~        Sun Mar 29 03:00:00 2009
--- include/glpstd.h    Mon Mar 30 15:33:04 2009
***************
*** 37,42 ****
--- 37,44 ----
  #include <string.h>
  #include <time.h>

+ #undef _G
+
  #endif

  /* eof */

The package then built correctly, and passed its validation test.

I suggest changing the initial underscores in local variables
and function arguments to be trailing underscores, in order
to easily avoid vendor namespaces.

Otherwise, the author(s) of glpk is(are) to be congratulated on its
portability.  I've routinely built it from version 4.29 onward on
about 25 flavors of Unix, and the success rate is almost universal.

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