[WIN32] Replace realpath function with absolute function

Since the "realpath" function is not available in the Windows operating system, it has been replaced by an "absolute" function available in both Windows and Linux operating systems.

- Replace "std::realpath" function with "std::filesystem::absolute" function.

**Self evaluation:**
1. Build test: [x]Passed []Failed []Skipped
2. Run test: [x]Passed []Failed []Skipped

Signed-off-by: Seungbaek Hong <sb92.hong@samsung.net>

nntrainer/app_context.cpp

@@ -393,7 +393,7 @@ void AppContext::setWorkingDirectory(const std::string &base) {
   }
   closedir(dir);
 
-  char *ret = realpath(base.c_str(), nullptr);
+  char *ret = getRealpath(base.c_str(), nullptr);
 
   if (ret == nullptr) {
     std::stringstream ss;

nntrainer/models/model_loader.cpp

@@ -470,7 +470,7 @@ int ModelLoader::loadFromConfig(std::string config, NeuralNetwork &model) {
 
   model_file_context = std::make_unique<AppContext>();
 
-  auto config_realpath_char = realpath(config.c_str(), nullptr);
+  auto config_realpath_char = getRealpath(config.c_str(), nullptr);
   if (config_realpath_char == nullptr) {
     ml_loge("failed to resolve config path to absolute path, reason: %s",
             strerror(errno));

nntrainer/utils/util_func.cpp

@@ -20,6 +20,10 @@
  *
  */
 
+#ifdef _WIN32
+#define MAX_PATH_LENGTH 1024
+#endif
+
 #include <cmath>
 #include <fstream>
 #include <random>
@@ -197,4 +201,12 @@ bool istrequal(const std::string &a, const std::string &b) {
   });
 }
 
+char *getRealpath(const char *__restrict name, char *__restrict resolved) {
+#ifdef _WIN32
+  return _fullpath(resolved, name, MAX_PATH_LENGTH);
+#else
+  return realpath(name, resolved);
+#endif
+}
+
 } // namespace nntrainer

nntrainer/utils/util_func.h

@@ -271,6 +271,16 @@ template <typename T, typename C = int> T enum_class_or(T e1, T e2) {
   return static_cast<T>(i1 | i2);
 }
 
+/**
+ * @brief Convert a relative path into an absolute path.
+ *
+ * @param name relative path
+ * @param resolved variable to store the result value.
+ *
+ * @return absolute path
+ */
+char *getRealpath(const char *__restrict name, char *__restrict resolved);
+
 } /* namespace nntrainer */
 
 #endif /* __cplusplus */