Fix invalid pointer arithmetic.

[nmh] / h / mh.h

diff --git a/h/mh.h b/h/mh.h
index 8823d91963bd343f695618c031aa059619f39957..ebd124d18d0faf13f85b29f42eb787a1a854eab7 100644 (file)
--- a/h/mh.h
+++ b/h/mh.h
@@ -3,6 +3,19 @@
 
 #include <h/nmh.h>
 
+/* It's undefined behaviour in C99 to convert from a function pointer to
+ * a data-object pointer, e.g. void pointer.  gcc's -pedantic warns of
+ * this and can stop compilation.  POSIX requires the operation however,
+ * e.g. for dlsym(3), and so we know it's safe on POSIX platforms, e.g.
+ * the pointers are of the same size.  Thus use a union to subvert gcc's
+ * check.  The function-pointer equivalent of a void pointer is any
+ * function-pointer type as all function pointers are defined to be
+ * convertible from one another;  use the simplest available. */
+typedef union {
+    void *v;
+    void (*f)(void);
+} generic_pointer;
+
 /*
  * Well-used constants
  */
@@ -22,13 +35,6 @@
  */
 #define NMH_BUFSIZ  max(BUFSIZ, 8192)
 
-#ifndef FALSE
-#define FALSE false
-#endif
-#ifndef TRUE
-#define TRUE true
-#endif
-
 /* If we're using gcc then tell it extra information so it can do more
  * compile-time checks. */
 #if __GNUC__ > 2
@@ -126,11 +132,60 @@ struct swit {
 
     char *sw;
 
-    /* The minchars field is apparently used like this:
+    /*
+     * The previous comments here about minchars was incorrect; this is
+     * (AFAIK) the correct information.
+     *
+     * A minchars of "0" means this switch can be abbreviated to any number
+     * of characters (assuming the abbreviation does not match any other
+     * switches).
+     *
+     * A positive value for minchars means that when the user specifies
+     * the switch on the command line, it MUST be at least that many
+     * characters.
+     *
+     * A negative value for minchars means that the user-given switch must
+     * be that many characters, but will NOT be shown in -help output.
+     *
+     * So what should I use?  Well, for nearly all switches you want to specify
+     * a minchars of 0.  smatch will report an error if the switch given
+     * matches more than one entry.  Let's say you have the following
+     * two switches: -append and -apply.  -app will return AMBIGSW from
+     * smatch. -appe and -appl will work fine.  So 0 is the correct choice
+     * here.
+     *
+     * The only time you want to specify a minimum length is if you have
+     * a switch who's name is a substring of a longer switch.  The example
+     * you see sometimes in the code is -form and -format.  If you gave a
+     * minchars of 0 for both, -form would match both -form AND -format,
+     * and you'd always get AMBIGSW.  The solution is to specify a minchars
+     * of 5 for -format; that way just -form will just match -form.  When
+     * a minchars is given, the -help output will specify the minimum
+     * switch length, like this:
+     *
+     * -(forma)t string
+     *
+     * A negative value works the same way, except the switch isn't printed
+     * in -help.  Why would you do that?  Well, there are a few instances
+     * of internal switches and some switches which only appear if a particular
+     * feature is enabled (such as SASL or TLS).  Lately I've been of the
+     * opinion that all switches should be specified, even if they are
+     * internal or use non-available features, but currently the smatch
+     * code still supports this.
+     *
+     * This isn't the appropriate place to make this note, but since I was
+     * here ... when creating switches, you should make a negation switch
+     * right after the enabling switch.  E.g. you should have:
+     *
+     * X("sasl", 0, SASLSW) \
+     * X("nosasl", 0, NOSASLSW) \
+     *
+     * in the switch array, because when you run -help, print_sw will detect
+     * this and output:
+     *
+     * -[no]sasl
+     */
 
-       -# : Switch can be abbreviated to # characters; switch hidden in -help.
-       0  : Switch can't be abbreviated;               switch shown in -help.
-       #  : Switch can be abbreviated to # characters; switch shown in -help. */
     int minchars;
 
     /*
@@ -519,6 +574,4 @@ extern char *version_str;
 extern char *whatnowproc;
 extern char *whomproc;
 
-extern void (*done) (int) NORETURN;
-
 #include <h/prototypes.h>