tinyobjloader · syoyo · Jul 15, 2025 · Jul 11, 2025 · Jul 13, 2025 · Jul 13, 2025
diff --git a/models/cube_w_BOM.mtl b/models/cube_w_BOM.mtl
@@ -0,0 +1,24 @@
+newmtl white
+Ka 0 0 0
+Kd 1 1 1
+Ks 0 0 0
+
+newmtl red
+Ka 0 0 0
+Kd 1 0 0
+Ks 0 0 0
+
+newmtl green
+Ka 0 0 0
+Kd 0 1 0
+Ks 0 0 0
+
+newmtl blue
+Ka 0 0 0
+Kd 0 0 1
+Ks 0 0 0
+
+newmtl light
+Ka 20 20 20
+Kd 1 1 1
+Ks 0 0 0
diff --git a/models/cube_w_BOM.obj b/models/cube_w_BOM.obj
@@ -0,0 +1,32 @@
+mtllib cube_w_BOM.mtl
+
+v 0.000000 2.000000 2.000000
+v 0.000000 0.000000 2.000000
+v 2.000000 0.000000 2.000000
+v 2.000000 2.000000 2.000000
+v 0.000000 2.000000 0.000000
+v 0.000000 0.000000 0.000000
+v 2.000000 0.000000 0.000000
+v 2.000000 2.000000 0.000000
+# 8 vertices
+
+g front cube
+usemtl white
+f 1 2 3 4
+# two white spaces between 'back' and 'cube'
+g back  cube
+# expects white material
+f 8 7 6 5
+g right cube
+usemtl red
+f 4 3 7 8
+g top cube
+usemtl white
+f 5 1 4 8
+g left cube
+usemtl green
+f 5 6 2 1
+g bottom cube
+usemtl white
+f 2 6 7 3
+# 6 elements
diff --git a/tests/tester.cc b/tests/tester.cc
@@ -1465,9 +1465,61 @@ void test_default_kd_for_multiple_materials_issue391() {
      std::cerr << "Unexpected material found!" << std::endl;
      TEST_CHECK(false);
    }
+  }  
+}
+
+void test_removeUtf8Bom() {
+  // Basic input with BOM
+  std::string withBOM = "\xEF\xBB\xBFhello world";
+  TEST_CHECK(tinyobj::removeUtf8Bom(withBOM) == "hello world");
+
+  // Input without BOM
+  std::string noBOM = "hello world";
+  TEST_CHECK(tinyobj::removeUtf8Bom(noBOM) == "hello world");
+
+  // Leaves short string unchanged
+  std::string shortStr = "\xEF";
+  TEST_CHECK(tinyobj::removeUtf8Bom(shortStr) == shortStr);
+
+  std::string shortStr2 = "\xEF\xBB";
+  TEST_CHECK(tinyobj::removeUtf8Bom(shortStr2) == shortStr2);
+
+  // BOM only returns empty string
+  std::string justBom = "\xEF\xBB\xBF";
+  TEST_CHECK(tinyobj::removeUtf8Bom(justBom) == "");
+
+  // Empty string
+  std::string emptyStr = "";
+  TEST_CHECK(tinyobj::removeUtf8Bom(emptyStr) == "");
+}
+
+void test_loadObj_with_BOM() {
+  tinyobj::attrib_t attrib;
+  std::vector<tinyobj::shape_t> shapes;
+  std::vector<tinyobj::material_t> materials;
+
+  std::string warn;
+  std::string err;
+  bool ret = tinyobj::LoadObj(&attrib, &shapes, &materials, &warn, &err,
+                              "../models/cube_w_BOM.obj", gMtlBasePath);
+
+  if (!warn.empty()) {
+    std::cout << "WARN: " << warn << std::endl;
+  }
+
+  if (!err.empty()) {
+    std::cerr << "ERR: " << err << std::endl;
  }
+
+  TEST_CHECK(true == ret);
+  TEST_CHECK(6 == shapes.size());
+  TEST_CHECK(0 == shapes[0].name.compare("front cube"));
+  TEST_CHECK(0 == shapes[1].name.compare("back cube"));  // multiple whitespaces
+                                                         // are aggregated as
+                                                         // single white space.
 }

+
 // Fuzzer test.
 // Just check if it does not crash.
 // Disable by default since Windows filesystem can't create filename of afl
@@ -1579,4 +1631,6 @@ TEST_LIST = {
     test_invalid_texture_vertex_index},
    {"default_kd_for_multiple_materials_issue391",
     test_default_kd_for_multiple_materials_issue391},
+    {"test_removeUtf8Bom", test_removeUtf8Bom},
+    {"test_loadObj_with_BOM", test_loadObj_with_BOM},
    {NULL, NULL}};
diff --git a/tiny_obj_loader.h b/tiny_obj_loader.h
@@ -810,6 +810,17 @@ static inline std::string toString(const T &t) {
  return ss.str();
 }

+static inline std::string removeUtf8Bom(const std::string& input) {
+    // UTF-8 BOM = 0xEF,0xBB,0xBF
+    if (input.size() >= 3 &&
+        static_cast<unsigned char>(input[0]) == 0xEF &&
+        static_cast<unsigned char>(input[1]) == 0xBB &&
+        static_cast<unsigned char>(input[2]) == 0xBF) {
+        return input.substr(3); // Skip BOM
+    }
+    return input;
+}
+
 struct warning_context {
  std::string *warn;
  size_t line_number;
@@ -2110,6 +2121,9 @@ void LoadMtl(std::map<std::string, int> *material_map,
    if (linebuf.empty()) {
      continue;
    }
+    if (line_no == 1) {
+      linebuf = removeUtf8Bom(linebuf);
+    }

    // Skip leading space.
    const char *token = linebuf.c_str();
@@ -2637,6 +2651,9 @@ bool LoadObj(attrib_t *attrib, std::vector<shape_t> *shapes,
    if (linebuf.empty()) {
      continue;
    }
+    if (line_num == 1) {
+      linebuf = removeUtf8Bom(linebuf);
+    }

    // Skip leading space.
    const char *token = linebuf.c_str();