Update example of building dll on Windows

meteorcloudy · Copybara-Service · commit a65ce6d547ee · 2019-02-12T01:42:44.000-08:00
Closes #7252. Change-Id: I9bc2d80deda291d3818c690fc3b36aacf62e0830 PiperOrigin-RevId: 233564393
diff --git a/examples/windows/dll/BUILD b/examples/windows/dll/BUILD
@@ -4,18 +4,66 @@ filegroup(
     visibility = ["//examples:__pkg__"],
 )
 
+cc_library(
+    name = "hello-library-header",
+    hdrs = ["hello-library.h"],
+)
+
 cc_binary(
     name = "hellolib.dll",
     srcs = [
         "hello-library.cpp",
     ],
+    # Define COMPILING_DLL to export symbols during compiling the DLL.
+    # See hello-library.h
+    copts = ["/DCOMPILING_DLL"],
     linkshared = 1,
+    deps = [
+        ":hello-library-header",
+    ],
 )
 
+# **Explicitly link to hellolib.dll**
+
+# Declare hellolib.dll as data dependency and load it explicitly in code.
 cc_binary(
-    name = "hello",
+    name = "hello_world-load-dll-at-runtime",
     srcs = [
-        "hello-world.cpp",
+        "hello_world-load-dll-at-runtime.cpp",
     ],
     data = [":hellolib.dll"],
 )
+
+# **Implicitly link to hellolib.dll**
+
+# Get the import library for hellolib.dll
+filegroup(
+    name = "hello_lib_import_lib",
+    srcs = [":hellolib.dll"],
+    output_group = "interface_library",
+)
+
+# Because we cannot directly depend on cc_binary from other cc rules in deps attribute,
+# we use cc_import as a bridge to depend on hellolib.dll
+cc_import(
+    name = "hellolib_dll_import",
+    interface_library = ":hello_lib_import_lib",
+    shared_library = ":hellolib.dll",
+)
+
+# Create a new cc_library to also include the headers needed for hellolib.dll
+cc_library(
+    name = "hellolib_dll",
+    deps = [
+        ":hello-library-header",
+        ":hellolib_dll_import",
+    ],
+)
+
+cc_binary(
+    name = "hello_world-link-to-dll-via-lib",
+    srcs = [
+        "hello_world-link-to-dll-via-lib.cpp",
+    ],
+    deps = [":hellolib_dll"],
+)
diff --git a/examples/windows/dll/hello-library.cpp b/examples/windows/dll/hello-library.cpp
@@ -1,23 +1,15 @@
 #include <stdio.h>
+#include <time.h>
 #include <windows.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-#include <time.h>
+#include "examples/windows/dll/hello-library.h"
 
-__declspec(dllexport) char *get_time() {
+DLLEXPORT char *get_time() {
   time_t ltime;
   time(&ltime);
   return ctime(&ltime);
 }
 
-__declspec(dllexport) void say_hello(char *message) {
+DLLEXPORT void say_hello(char *message) {
   printf("Hello from dll!\n%s", message);
 }
-
-#ifdef __cplusplus
-}
-#endif
-
diff --git a/examples/windows/dll/hello-library.h b/examples/windows/dll/hello-library.h
@@ -0,0 +1,13 @@
+#ifndef HELLO_LIBRARY_H
+#define HELLO_LIBRARY_H
+
+#ifdef COMPILING_DLL
+#define DLLEXPORT __declspec(dllexport)
+#else
+#define DLLEXPORT __declspec(dllimport)
+#endif
+
+extern "C" DLLEXPORT char *get_time();
+extern "C" DLLEXPORT void say_hello(char *);
+
+#endif
diff --git a/examples/windows/dll/hello_world-link-to-dll-via-lib.cpp b/examples/windows/dll/hello_world-link-to-dll-via-lib.cpp
@@ -0,0 +1,7 @@
+#include "examples/windows/dll/hello-library.h"
+
+int main() {
+  char *now = get_time();
+  say_hello(now);
+  return 0;
+}
diff --git a/examples/windows/dll/hello_world-load-dll-at-runtime.cpp b/examples/windows/dll/hello_world-load-dll-at-runtime.cpp
