Writing C string to a C-allocated buffer from Go

howto.txt

# Project tree:
$  tree
.
├── go
│   ├── go.mod
│   └── strcpy.go
└── run.c

# Build DLL from Go code:
$ cd go
go$ CGO_ENABLED=1 CC=/usr/bin/i686-w64-mingw32-gcc GOOS=windows GOARCH=386 go build -buildmode=c-shared -o ../strcpy.dll

# Return back and build the executable which loads the DLL:
go$ cd ..
$ /usr/bin/i686-w64-mingw32-gcc -o run run.c -L`pwd` -lstrcpy

# Analyze the result:
$ file run.exe 
run.exe: PE32 executable (console) Intel 80386, for MS Windows

# Run the resulting executable:
$ wine run.exe
2022/09/09 16:32:07 Test func exec start ...
2022/09/09 16:32:07 Test func exec end ...
test_driver_success

Makefile

CC = /usr/bin/i686-w64-mingw32-gcc
GOOS = windows
GOARCH = 386
CGO_ENABLED = 1

export CC GOOS GOARCH CGO_ENABLED

.PHONY: all build run clean

all: run

build: run.exe

clean:
	@rm run.exe
	@rm strcpy.dll

run: run.exe
	wine run.exe

strcpy.dll: go/strcpy.go
	cd $(CURDIR)/go && \
	go build -buildmode=c-shared -o ../strcpy.dll

run.exe: run.c strcpy.dll
	$(CC) -o $@ run.c -L$(CURDIR) -lstrcpy

run.c

#include <stdlib.h>
#include <stdio.h>

extern void Test(char* params, int count, char* result);

int main(void)
{
	char *p;

	p = malloc(1000);
	if (p == NULL) {
		fputs("malloc failed\n", stderr);
		return 2;
	}

	Test(NULL, 1, p);

	puts(p);

	free(p);
}

strcpy.go

package main

// #include <string.h>
// #cgo windows LDFLAGS: -static-libgcc -static
import "C"

import "log"

//export Test
func Test(ptrParams *C.char, count C.int, resultStr *C.char) int {
	log.Println("Test func exec start ...")
	str := "test_driver_success"
	C.strcpy(resultStr, C.CString(str))
	log.Println("Test func exec end ...")
	return 0
}

func main() {}