opt: Don't segfault if a string's default is NULL

Instead show '(nil)', like other people do. This is distinguishable
from a similar looking string value, because the latter is shown with
double quotes while NULL's nil has no quotes.

Signed-off-by: Douglas Bagnall <douglas@halo.gen.nz>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/ccan/opt/helpers.c b/ccan/opt/helpers.c
index c557f96d8488d01d3e1297ea235f6c2c8b76fb4f..43b86d7ca2ad953665522cf37f449b8046ffd3b7 100644 (file)
--- a/ccan/opt/helpers.c
+++ b/ccan/opt/helpers.c
@@ -202,14 +202,19 @@ void opt_show_invbool(char buf[OPT_SHOW_LEN], const bool *b)
 
 void opt_show_charp(char buf[OPT_SHOW_LEN], char *const *p)
 {
 
 void opt_show_charp(char buf[OPT_SHOW_LEN], char *const *p)
 {

-       size_t len = strlen(*p);
-       buf[0] = '"';
-       if (len > OPT_SHOW_LEN - 2)
-               len = OPT_SHOW_LEN - 2;
-       strncpy(buf+1, *p, len);
-       buf[1+len] = '"';
-       if (len < OPT_SHOW_LEN - 2)
-               buf[2+len] = '\0';
+       if (*p){
+               size_t len = strlen(*p);
+               buf[0] = '"';
+               if (len > OPT_SHOW_LEN - 2)
+                       len = OPT_SHOW_LEN - 2;
+               strncpy(buf+1, *p, len);
+               buf[1+len] = '"';
+               if (len < OPT_SHOW_LEN - 2)
+                       buf[2+len] = '\0';
+       }
+       else {
+               strncpy(buf, "(nil)", OPT_SHOW_LEN);
+       }

 }
 
 /* Show an integer value, various forms. */
 }
 
 /* Show an integer value, various forms. */