From e3d10c994d3abf47706ee2fb9b09cde2c3300208 Mon Sep 17 00:00:00 2001
From: Terry Golubiewski <tjgolubi@netins.net>
Date: Sun, 8 Nov 2026 08:10:13 -0800
Subject: [PATCH] fix: avoid null pointers in zero-length string comparisons
 (#5014)

Return zero from detail::compare when n == 0. Sanitizer checking reported
null pointers being passed to memcmp when comparing empty string views,
even though the comparison length was zero.
---
 include/fmt/core.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/fmt/core.h b/include/fmt/core.h
index 1bcf6442..0d675baf 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -462,6 +462,7 @@ constexpr FMT_ALWAYS_INLINE auto narrow(const char* s) -> const char* {
 
 template <typename Char>
 FMT_CONSTEXPR auto compare(const Char* s1, const Char* s2, size_t n) -> int {
+  if (n == 0) return 0;
   if (!is_constant_evaluated() && sizeof(Char) == 1) return memcmp(s1, s2, n);
   for (; n != 0; ++s1, ++s2, --n) {
     if (*s1 < *s2) return -1;