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From: Jelte Fennema-Nio <[email protected]>
To: PostgreSQL Hackers <[email protected]>
To: Thomas Munro <[email protected]>
Subject: Make copyObject work in C++
Date: Fri, 5 Dec 2025 15:46:57 +0100
Message-ID: <CAGECzQR21OnnKiZO_1rLWO0-16kg1JBxnVq-wymYW0-_1cUNtg@mail.gmail.com> (raw)

Calling copyObject fails in C++ with an error like in most setups:

error: use of undeclared identifier 'typeof'; did you mean 'typeid'

This is due to the C compiler supporting used to compile postgres
supporting typeof, but that function actually not being present in the
C++ compiler. This fixes that by using decltype instead of typeof when
including the header in C++.

Realized because of Thomas' not about how much of our headers should
work in C++, and remembering I hit this specific problem myself.

Another approach would be to force the value of HAVE_TYPEOF to 0 if __cplusplus.


Attachments:

  [application/x-patch] v1-0001-Make-copyObject-work-in-C.patch (1.3K, 2-v1-0001-Make-copyObject-work-in-C.patch)
  download | inline diff:
From 7ce44917fe789e394193ff20e3b88b2e82f96c20 Mon Sep 17 00:00:00 2001
From: Jelte Fennema-Nio <[email protected]>
Date: Fri, 5 Dec 2025 15:37:59 +0100
Subject: [PATCH v1] Make copyObject work in C++

Calling copyObject fails in C++ with an error like in most setups:

error: use of undeclared identifier 'typeof'; did you mean 'typeid'

This is due to the C compiler supporting used to compile postgres
supporting typeof, but that function actually not being present in the
C++ compiler. This fixes that by using decltype instead of typeof when
including the header in C++.
---
 src/include/nodes/nodes.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index fb3957e75e5..5a4fa8260f2 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -226,7 +226,9 @@ extern int16 *readAttrNumberCols(int numCols);
 extern void *copyObjectImpl(const void *from);
 
 /* cast result back to argument type, if supported by compiler */
-#ifdef HAVE_TYPEOF
+#if defined(__cplusplus)
+#define copyObject(obj) ((decltype(obj)) copyObjectImpl(obj))
+#elif defined(HAVE_TYPEOF)
 #define copyObject(obj) ((typeof(obj)) copyObjectImpl(obj))
 #else
 #define copyObject(obj) copyObjectImpl(obj)

base-commit: 4d936c3fff1ac8dead2cc240ba3da2ed6337257c
-- 
2.52.0

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