diff --git a/include/tmp/file b/include/tmp/file
index 74163b4..6513e70 100644
--- a/include/tmp/file
+++ b/include/tmp/file
@@ -7,10 +7,12 @@
 #define TMP_FILE_H
 
 #include <cstddef>
+#include <cstdio>
 #include <filesystem>
 #include <fstream>
 #include <ios>
 #include <istream>
+#include <memory>
 
 #ifdef __GLIBCXX__
 #include <ext/stdio_filebuf.h>
@@ -18,6 +20,18 @@
 
 namespace tmp {
 
+/// Implementation-defined handle type to the file
+#if defined(_WIN32)
+using file_native_handle = void*;    // HANDLE
+#elif __has_include(<unistd.h>)
+using file_native_handle = int;    // POSIX file descriptor
+#else
+#error "Target platform not supported"
+#endif
+
+extern "C++" std::FILE* create_file();
+extern "C++" file_native_handle get_native_handle(std::FILE* file) noexcept;
+
 /// tmp::file is a smart handle that manages a binary temporary file, ensuring
 /// its deletion when the handle goes out of scope
 ///
@@ -53,17 +67,27 @@ namespace tmp {
 class file : public std::iostream {
 public:
   /// Implementation-defined handle type to the file
-#if defined(_WIN32)
-  using native_handle_type = void*;    // HANDLE
-#elif __has_include(<unistd.h>)
-  using native_handle_type = int;    // POSIX file descriptor
-#else
-#error "Target platform not supported"
-#endif
+  using native_handle_type = file_native_handle;
 
   /// Creates and opens a binary temporary file as if by POSIX `tmpfile`
   /// @throws std::filesystem::filesystem_error if cannot create a file
-  explicit file();
+  explicit file()
+      : std::iostream(std::addressof(sb)),
+        underlying(create_file(), &std::fclose) {
+#if defined(_MSC_VER)
+    sb = std::filebuf(underlying.get());
+#elif defined(_LIBCPP_VERSION)
+    sb.__open(fileno(underlying.get()), binary | in | out);
+#else
+    sb = __gnu_cxx::stdio_filebuf<char>(underlying.get(), binary | in | out);
+#endif
+
+    if (!sb.is_open()) {
+      std::error_code ec = std::make_error_code(std::io_errc::stream);
+      throw std::filesystem::filesystem_error("Cannot create a temporary file",
+                                              ec);
+    }
+  }
 
   file(const file&) = delete;
   file& operator=(const file&) = delete;
@@ -87,7 +111,9 @@ public:
 
   /// Returns an implementation-defined handle to this file
   /// @returns The underlying implementation-defined handle
-  native_handle_type native_handle() const noexcept;
+  native_handle_type native_handle() const noexcept {
+    return get_native_handle(underlying.get());
+  }
 
   /// Closes and deletes this file
   ~file() noexcept override = default;
diff --git a/src/abi.hpp b/src/abi.hpp
index ea6a7aa..31d21da 100644
--- a/src/abi.hpp
+++ b/src/abi.hpp
@@ -4,6 +4,7 @@
 #ifndef TMP_ABI_H
 #define TMP_ABI_H
 
+#include <cstdio>
 #include <filesystem>
 #include <string_view>
 
@@ -15,10 +16,16 @@
 
 namespace tmp {
 
-std::filesystem::path abi create_directory(std::string_view prefix);
-void abi remove_all(const std::filesystem::path& path) noexcept;
+auto abi create_directory(std::string_view prefix) -> std::filesystem::path;
+auto abi remove_all(const std::filesystem::path& path) noexcept -> void;
 
-class abi file;
+auto abi create_file() -> std::FILE*;
+auto abi get_native_handle(std::FILE* file) noexcept ->
+#if defined(_WIN32)
+    void*;
+#elif __has_include(<unistd.h>)
+    int;
+#endif
 }    // namespace tmp
 
 #endif    // TMP_ABI_H
diff --git a/src/directory.cpp b/src/directory.cpp
index 636a633..8d81af4 100644
--- a/src/directory.cpp
+++ b/src/directory.cpp
@@ -22,6 +22,7 @@
 
 namespace tmp {
 namespace {
+
 namespace fs = std::filesystem;
 
 /// Checks if the given prefix is valid to attach to a temporary directory name
diff --git a/src/file.cpp b/src/file.cpp
index 6115789..27c12fa 100644
--- a/src/file.cpp
+++ b/src/file.cpp
@@ -23,7 +23,6 @@
 #endif
 
 namespace tmp {
-namespace {
 
 namespace fs = std::filesystem;
 
@@ -35,22 +34,6 @@ static_assert(std::is_trivially_copyable_v<file::native_handle_type>);
 static_assert(std::is_same_v<HANDLE, file::native_handle_type>);
 #endif
 
-#ifndef _MSC_VER
-/// Open mode for binary temporary files
-constexpr auto mode = std::ios::binary | std::ios::in | std::ios::out;
-#endif
-
-/// Returns an implementation-defined handle to the file
-/// @param[in] file The file to the native handle for
-/// @returns The underlying implementation-defined handle
-file::native_handle_type get_native_handle(std::FILE* file) noexcept {
-#ifdef _WIN32
-  return reinterpret_cast<HANDLE>(_get_osfhandle(_fileno(file)));
-#else
-  return fileno(file);
-#endif
-}
-
 /// Creates and opens a binary temporary file as if by POSIX `tmpfile`
 /// @returns A pointer to the file stream associated with the temporary file
 /// @throws fs::filesystem_error if cannot create a temporary file
@@ -63,26 +46,15 @@ std::FILE* create_file() {
 
   return file;
 }
-}    // namespace
 
-file::file()
-    : std::iostream(std::addressof(sb)),
-      underlying(create_file(), &std::fclose) {
-#if defined(_MSC_VER)
-  sb = std::filebuf(underlying.get());
-#elif defined(_LIBCPP_VERSION)
-  sb.__open(get_native_handle(underlying.get()), mode);
+/// Returns an implementation-defined handle to the file
+/// @param[in] file The file to the native handle for
+/// @returns The underlying implementation-defined handle
+file::native_handle_type get_native_handle(std::FILE* file) noexcept {
+#ifdef _WIN32
+  return reinterpret_cast<HANDLE>(_get_osfhandle(_fileno(file)));
 #else
-  sb = __gnu_cxx::stdio_filebuf<char>(underlying.get(), mode);
+  return fileno(file);
 #endif
-
-  if (!sb.is_open()) {
-    std::error_code ec = std::make_error_code(std::io_errc::stream);
-    throw fs::filesystem_error("Cannot create a temporary file", ec);
-  }
-}
-
-file::native_handle_type file::native_handle() const noexcept {
-  return get_native_handle(underlying.get());
 }
 }    // namespace tmp