From 3450df07b562f4c66af67f5b7f5d6e92c8fd3a3d Mon Sep 17 00:00:00 2001
From: Sergiu Deitsch <sergiu.deitsch@gmail.com>
Date: Fri, 25 Mar 2022 22:19:21 +0100
Subject: [PATCH] workaround msvc issue with C++17 consumer

---
 CXSparse/Include/cs.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/CXSparse/Include/cs.h b/CXSparse/Include/cs.h
index 2a7acff1a..1409392e3 100644
--- a/CXSparse/Include/cs.h
+++ b/CXSparse/Include/cs.h
@@ -31,6 +31,22 @@
 #include "cs_export.h"
 
 #ifndef NCOMPLEX
+/*
+ * A workaround for Visual Studio 2022 which does not define _Dcomplex if the
+ * consumer enabled the /std:c++17 flag. In this case, <complex.h> includes
+ * <ccomplex> which in turn includes <complex> that omits the necessary type
+ * definition.
+ */
+#if defined(__cplusplus) && defined(_MSC_VER)
+/* Adjust the definition of _CRT_USE_C_COMPLEX_H unless it is already defined
+ * and at the same time is non zero */
+#  if !(defined(_CRT_USE_C_COMPLEX_H) && !_CRT_USE_C_COMPLEX_H)
+#    if defined(_CRT_USE_C_COMPLEX_H)
+#      undef _CRT_USE_C_COMPLEX_H
+#    endif
+#    define _CRT_USE_C_COMPLEX_H 1
+#  endif
+#endif
 #include <complex.h>
 #endif /* !defined(NCOMPLEX) */