DOC: update sample calc.c to match doc

Author: kamahen

man/calc.c

@@ -1,19 +1,30 @@
+#include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <SWI-Prolog.h>
 
-#define MAXLINE 1024
-
 int
 main(int argc, char **argv)
-{ char expression[MAXLINE];
-  char *e = expression;
+{ char *expression;
   char *program = argv[0];
-  char *plav[2];
-  int n;
 
-  /* combine all the arguments in a single string */
+  if ( argc < 2 )
+  { fprintf(stderr, "Usage: %s expression\n", program);
+    exit(1);
+  }
+
+  /* Determine length of joined arguments */
+  size_t len = 1 + argc - 2;
+  for(int n=1; n<argc; n++)
+    len += strlen(argv[n]);
+  if ( !(expression = malloc(len)) ) // freed on exit
+  { perror("allocate");
+    exit(1);
+  }
 
-  for(n=1; n<argc; n++)
+  /* combine all the arguments as a single string */
+  char *e = expression;
+  for(int n=1; n<argc; n++)
   { if ( n != 1 )
       *e++ = ' ';
     strcpy(e, argv[n]);
@@ -22,24 +33,27 @@ main(int argc, char **argv)
 
   /* make the argument vector for Prolog */
 
-  plav[0] = program;
-  plav[1] = NULL;
+  int   plac=0;
+  char *plav[2];
+  plav[plac++] = program;
+  plav[plac]   = NULL;
 
   /* initialise Prolog */
 
-  if ( !PL_initialise(1, plav) )
+  if ( !PL_initialise(plac, plav) )
     PL_halt(1);
 
   /* Lookup calc/1 and make the arguments and call */
 
   { predicate_t pred = PL_predicate("calc", 1, "user");
-    term_t h0 = PL_new_term_refs(1);
-    int rval;
+    bool rc;
+    term_t h0;
 
-    PL_put_atom_chars(h0, expression);
-    rval = PL_call_predicate(NULL, PL_Q_NORMAL, pred, h0);
+    rc = ( (h0=PL_new_term_refs(1)) &&
+	   PL_unify_chars(h0, PL_STRING|REP_MB, (size_t)-1, expression) &&
+	   PL_call_predicate(NULL, PL_Q_NORMAL, pred, h0) );
 
-    PL_halt(rval ? 0 : 1);
+    PL_halt(!rc);
   }
 
   return 0;