diff --git a/src/util_opengl.h b/src/util_opengl.h
index 0f3325f..2ad6ed4 100644
--- a/src/util_opengl.h
+++ b/src/util_opengl.h
@@ -12,8 +12,8 @@
 namespace acg {
 
 std::string load_file_as_string(
-    const std::string &fname) {
-  std::ifstream inputFile1(fname.c_str());
+    const char* fname) {
+  std::ifstream inputFile1(fname);
   std::istreambuf_iterator<char> vdataBegin(inputFile1);
   std::istreambuf_iterator<char> vdataEnd;
   return {vdataBegin, vdataEnd};
diff --git a/task04/main.cpp b/task04/main.cpp
index de11e42..4a436db 100644
--- a/task04/main.cpp
+++ b/task04/main.cpp
@@ -69,10 +69,10 @@ int main() {
 
   int shaderProgram;
   { // compile shader program
-    std::string vrt_path = std::filesystem::path(PROJECT_SOURCE_DIR) / "shader.vert";
-    std::string frg_path = std::filesystem::path(PROJECT_SOURCE_DIR) / "shader.frag";
-    std::string vrt = acg::load_file_as_string(vrt_path); // read source code of vertex shader program
-    std::string frg = acg::load_file_as_string(frg_path); // read source code of fragment shader program
+    const auto vrt_path = std::filesystem::path(PROJECT_SOURCE_DIR) / "shader.vert";
+    const auto frg_path = std::filesystem::path(PROJECT_SOURCE_DIR) / "shader.frag";
+    std::string vrt = acg::load_file_as_string(vrt_path.string().c_str()); // read source code of vertex shader program
+    std::string frg = acg::load_file_as_string(frg_path.string().c_str()); // read source code of fragment shader program
     shaderProgram = acg::create_shader_program(vrt, frg); // compile the shader on GPU
   }
   ::glUseProgram(shaderProgram); // use the shader program