From 977d47f3330d0f07a32624d6fa1e519f6e098687 Mon Sep 17 00:00:00 2001
From: Erik Auerswald <auerswal@unix-ag.uni-kl.de>
Date: Tue, 13 Jan 2026 09:06:09 +0100
Subject: [PATCH] avoid crash with option -0

Instead of using the possible option character '0' (ASCII value 0x30)
to indicate a long option without a short alias, use the value 0 as
indicator.  This value is treated specially by the used option parsing
code, and might even be the intended value to use for long-only options.

Before, using option `-0` sometimes, but not always, resulted in a
crash with `Segmentation fault (core dumped)`.

This fixes GitHub issue #456.
---
 CHANGELOG.md |  1 +
 src/fping.c  | 14 +++++++-------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 25b40be..84129eb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ Next
   recvmsg with MSG_DONTWAIT instead (#449)
 - Improved compatibility with NetBSD (#452, thanks @auerswal)
 - Consistent variable names for command-line options (#453, thanks @gsnw-sebast)
+- Avoid crash with option `-0` (#457, thanks @auerswal)
 
 fping 5.5 (2025-12-31)
 ======================
diff --git a/src/fping.c b/src/fping.c
index 7ac8889..064da20 100644
--- a/src/fping.c
+++ b/src/fping.c
@@ -661,7 +661,7 @@ int main(int argc, char **argv)
         { "vcount", 'C', OPTPARSE_REQUIRED },
         { "rdns", 'd', OPTPARSE_NONE },
         { "timestamp", 'D', OPTPARSE_NONE },
-        { "timestamp-format", '0', OPTPARSE_REQUIRED },
+        { "timestamp-format", 0, OPTPARSE_REQUIRED },
         { "elapsed", 'e', OPTPARSE_NONE },
         { "file", 'f', OPTPARSE_REQUIRED },
         { "generate", 'g', OPTPARSE_NONE },
@@ -670,7 +670,7 @@ int main(int argc, char **argv)
         { "interval", 'i', OPTPARSE_REQUIRED },
         { "iface", 'I', OPTPARSE_REQUIRED },
         { "json", 'J', OPTPARSE_NONE },
-        { "icmp-timestamp", '0', OPTPARSE_NONE },
+        { "icmp-timestamp", 0, OPTPARSE_NONE },
 #ifdef SO_MARK
         { "fwmark", 'k', OPTPARSE_REQUIRED },
 #endif
@@ -694,10 +694,10 @@ int main(int argc, char **argv)
         { "version", 'v', OPTPARSE_NONE },
         { "reachable", 'x', OPTPARSE_REQUIRED },
         { "fast-reachable", 'X', OPTPARSE_REQUIRED },
-        { "check-source", '0', OPTPARSE_NONE },
-        { "print-tos", '0', OPTPARSE_NONE },
-        { "print-ttl", '0', OPTPARSE_NONE },
-        { "seqmap-timeout", '0', OPTPARSE_REQUIRED },
+        { "check-source", 0, OPTPARSE_NONE },
+        { "print-tos", 0, OPTPARSE_NONE },
+        { "print-ttl", 0, OPTPARSE_NONE },
+        { "seqmap-timeout", 0, OPTPARSE_REQUIRED },
 #if defined(DEBUG) || defined(_DEBUG)
         { NULL, 'z', OPTPARSE_REQUIRED },
 #endif
@@ -707,7 +707,7 @@ int main(int argc, char **argv)
     double opt_val_double;
     while ((c = optparse_long(&optparse_state, longopts, NULL)) != EOF) {
         switch (c) {
-        case '0':
+        case 0:
             if(strstr(optparse_state.optlongname, "timestamp-format") != NULL) {
                 if(strcmp(optparse_state.optarg, "ctime") == 0) {
                   opt_timestamp_format = 1;
-- 
2.43.0