Add printf format utility

Add a template for obtaining a format string at build for a
built-in C++ type.

Change-Id: I8e5d26d4481b3ddafb5ffddbb058a1c75b3a2257
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>

2 files changed, 98 insertions, 0 deletions

diff --git a/src/data_types.hpp b/src/data_types.hpp
index af0ef68..439045e 100644
--- a/src/data_types.hpp
+++ b/src/data_types.hpp
@@ -80,6 +80,21 @@ using PropertyIndex = TupleRefMap <
         const std::string,
         const std::string >;
 // *INDENT-ON*
+
+/** @brief Convert some C++ types to others.
+ *
+ *  Remove type decorators to reduce template specializations.
+ *
+ *  1. Remove references.
+ *  2. Remove 'const' and 'volatile'.
+ */
+template <typename T> struct Downcast
+{
+    using Type = std::remove_cv_t<std::remove_reference_t<T>>;
+};
+template <typename T> using DowncastType =
+    typename Downcast<T>::Type;
+
 } // namespace monitoring
 } // namespace dbus
 } // namespace phosphor
diff --git a/src/format.hpp b/src/format.hpp
new file mode 100644
index 0000000..9c8341c
--- /dev/null
+++ b/src/format.hpp
@@ -0,0 +1,83 @@
+#pragma once
+
+#include "data_types.hpp"
+
+namespace phosphor
+{
+namespace dbus
+{
+namespace monitoring
+{
+namespace detail
+{
+
+/** @brief Map format strings to undecorated C++ types. */
+template <typename T> struct GetFormatType
+{
+
+};
+template <> struct GetFormatType<char>
+{
+    static constexpr auto format = "=%hhd";
+};
+template <> struct GetFormatType<short int>
+{
+    static constexpr auto format = "=%hd";
+};
+template <> struct GetFormatType<int>
+{
+    static constexpr auto format = "=%d";
+};
+template <> struct GetFormatType<long int>
+{
+    static constexpr auto format = "=%ld";
+};
+template <> struct GetFormatType<long long int>
+{
+    static constexpr auto format = "=%lld";
+};
+template <> struct GetFormatType<unsigned char>
+{
+    static constexpr auto format = "=%hhd";
+};
+template <> struct GetFormatType<unsigned short int>
+{
+    static constexpr auto format = "=%hd";
+};
+template <> struct GetFormatType<unsigned int>
+{
+    static constexpr auto format = "=%d";
+};
+template <> struct GetFormatType<unsigned long int>
+{
+    static constexpr auto format = "=%ld";
+};
+template <> struct GetFormatType<unsigned long long int>
+{
+    static constexpr auto format = "=%lld";
+};
+template <> struct GetFormatType<std::string>
+{
+    static constexpr auto format = "=%s";
+};
+template <> struct GetFormatType<char*>
+{
+    static constexpr auto format = "=%s";
+};
+template <> struct GetFormatType<const char*>
+{
+    static constexpr auto format = "=%s";
+};
+
+} // namespace detail
+
+/** @brief Get the format string for a C++ type. */
+template <typename T> struct GetFormat
+{
+    static constexpr auto format =
+        detail::GetFormatType<DowncastType<T>>::format;
+};
+
+} // namespace monitoring
+} // namespace dbus
+} // namespace phosphor