From a8ee202a434b6929a2f5488be5b1c0a0e10d6c02 Mon Sep 17 00:00:00 2001
From: Jeff Carr <jcarr@wit.com>
Date: Sat, 1 Nov 2025 10:26:18 -0500
Subject: example .c file on windows

---
 Makefile                | 13 +++++++++
 add_two.c               | 19 +++++++++++++
 adder.go                | 23 +++++++++++++++
 windowsCfileExample.txt | 74 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 129 insertions(+)
 create mode 100644 add_two.c
 create mode 100644 adder.go
 create mode 100644 windowsCfileExample.txt

diff --git a/Makefile b/Makefile
index ab46d8f..8da6b67 100644
--- a/Makefile
+++ b/Makefile
@@ -20,3 +20,16 @@ clean:
 	rm -f *.pb.go *.patch
 	-rm -f go.*
 	-go-mod-clean purge
+
+build:
+	go build -o add_two.dll -buildmode=c-shared
+	# PS D:\C\myextension> go build -o add_two.dll -buildmode=c-shared
+	# In PostgreSQL: open the query window (adjust path to your generated dynamically loaded library and header file (.dll, .h).
+	# CREATE FUNCTION add_two(int4) RETURNS int4
+	# AS 'D:/C/myextension/add_two.dll', 'add_two'
+	# LANGUAGE C STRICT;
+	# And finally test it:
+	# SELECT add_two(10)
+	# Result:
+		# add_two (integer)
+		# 1 	13
diff --git a/add_two.c b/add_two.c
new file mode 100644
index 0000000..78a268f
--- /dev/null
+++ b/add_two.c
@@ -0,0 +1,19 @@
+#include "postgres.h"
+#include "fmgr.h"
+
+
+PG_MODULE_MAGIC;
+
+
+extern int32 Adder(int32);
+
+
+PG_FUNCTION_INFO_V1(add_two);
+
+
+Datum
+add_two(PG_FUNCTION_ARGS)
+{
+    int32 arg = PG_GETARG_INT32(0);
+    PG_RETURN_INT32(Adder(arg));
+}
diff --git a/adder.go b/adder.go
new file mode 100644
index 0000000..351a9f0
--- /dev/null
+++ b/adder.go
@@ -0,0 +1,23 @@
+package main
+
+
+/*
+#cgo CFLAGS: -DWIN32 -ID:/pg18headers -ID:/pg18headers/port/win32
+#cgo LDFLAGS: -LD:/pg18lib
+#include "postgres.h"
+#include "fmgr.h"
+
+
+// Forward declare the C function so cgo compiles add_two.c too.
+extern void init_add_two();
+*/
+import "C"
+
+
+//export Adder
+func Adder(a C.int32) C.int32 {
+    return a + 3
+}
+
+
+func main() {}
diff --git a/windowsCfileExample.txt b/windowsCfileExample.txt
new file mode 100644
index 0000000..f4493ad
--- /dev/null
+++ b/windowsCfileExample.txt
@@ -0,0 +1,74 @@
+https://www.reddit.com/r/golang/comments/1ol2tqv/write_postgresql_functions_in_go_golang_example/
+
+
+Write PostgreSQL functions in Go Golang example
+
+It took me a while to figure this out. Go compiles the C files automatically.
+
+add_two.c
+
+#include "postgres.h"
+#include "fmgr.h"
+
+
+PG_MODULE_MAGIC;
+
+
+extern int32 Adder(int32);
+
+
+PG_FUNCTION_INFO_V1(add_two);
+
+
+Datum
+add_two(PG_FUNCTION_ARGS)
+{
+    int32 arg = PG_GETARG_INT32(0);
+    PG_RETURN_INT32(Adder(arg));
+}
+
+adder.go
+
+package main
+
+
+/*
+#cgo CFLAGS: -DWIN32 -ID:/pg18headers -ID:/pg18headers/port/win32
+#cgo LDFLAGS: -LD:/pg18lib
+#include "postgres.h"
+#include "fmgr.h"
+
+
+// Forward declare the C function so cgo compiles add_two.c too.
+extern void init_add_two();
+*/
+import "C"
+
+
+//export Adder
+func Adder(a C.int32) C.int32 {
+    return a + 3
+}
+
+
+func main() {}
+
+Compile it
+
+PS D:\C\myextension> go build -o add_two.dll -buildmode=c-shared
+
+In PostgreSQL: open the query window (adjust path to your generated dynamically loaded library and header file (.dll, .h).
+
+CREATE FUNCTION add_two(int4) RETURNS int4
+
+AS 'D:/C/myextension/add_two.dll', 'add_two'
+
+LANGUAGE C STRICT;
+
+And finally test it:
+
+SELECT add_two(10)
+
+Result:
+	add_two (integer)
+1 	13
-- 
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