From 2bfd96c9e0134e12cc69af95cbe9f416b1ad0f47 Mon Sep 17 00:00:00 2001
From: deepend-tildeclub <58404188+deepend-tildeclub@users.noreply.github.com>
Date: Mon, 16 Feb 2026 00:45:59 -0700
Subject: [PATCH] Fix vsnprintf handling for MSVC compiler

Add handling for MSVC's vsnprintf behavior
---
 src/common/sysinfo/win32/backend.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/common/sysinfo/win32/backend.c b/src/common/sysinfo/win32/backend.c
index be6df1b9..b2ed3ab8 100644
--- a/src/common/sysinfo/win32/backend.c
+++ b/src/common/sysinfo/win32/backend.c
@@ -588,7 +588,16 @@ static char *zoitechat_strdup_printf (const char *format, ...)
 
 	va_start (args, format);
 	va_copy (args_copy, args);
+	/*
+	 * MSVC's debug CRT treats vsnprintf(NULL, 0, ...) as an invalid parameter,
+	 * which triggers a fatal runtime exception via ucrtbased.dll. Use
+	 * _vscprintf() to determine required output length on that toolchain.
+	 */
+#ifdef _MSC_VER
+	length = _vscprintf (format, args_copy);
+#else
 	length = vsnprintf (NULL, 0, format, args_copy);
+#endif	
 	va_end (args_copy);
 
 	if (length < 0)