add get_version() for c_api. (facebookresearch#3688)

Summary:
Pull Request resolved: facebookresearch#3688
Looks like our previous changes only modified the cpp API. Not the c_api like the request wanted. This attempts to add faiss_get_version to c_api

Reviewed By: ramilbakhshyiev

Differential Revision: D60207739

fbshipit-source-id: 07184aeae92a154bb3f440279595077f002851f3

c_api/CMakeLists.txt

@@ -30,6 +30,7 @@ set(FAISS_C_SRC
   index_io_c.cpp
   impl/AuxIndexStructures_c.cpp
   utils/distances_c.cpp
+  utils/utils_c.cpp
 )
 add_library(faiss_c ${FAISS_C_SRC})
 target_link_libraries(faiss_c PRIVATE faiss)

c_api/utils/utils_c.cpp

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// Copyright 2004-present Facebook. All Rights Reserved.
+// -*- c++ -*-
+
+#include "utils_c.h"
+#include <faiss/Index.h>
+
+const char* faiss_get_version() {
+    return VERSION_STRING;
+}

c_api/utils/utils_c.h

@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// Copyright 2004-present Facebook. All Rights Reserved.
+// -*- c -*-
+
+#ifndef FAISS_UTILS_C_H
+#define FAISS_UTILS_C_H
+
+#include <stdint.h>
+#include <stdlib.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+const char* faiss_get_version();
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif