Revised following code review by @hassec. Thank You, Christoph.

include/exiv2/bmffimage.hpp

@@ -32,7 +32,7 @@ namespace Exiv2
 {
     EXIV2API bool enableBMFF(bool enable = true);
 
-    class Iloc;  // We'll define this in bmffimage.cpp
+    struct Iloc;  // We'll define this in bmffimage.cpp
 
     // *****************************************************************************
     // class definitions
@@ -131,10 +131,7 @@ namespace Exiv2
         uint64_t visits_max_;
         std::string indent(int i)
         {
-            std::string r;
-            while (i-- > 0)
-                r += std::string("  ");
-            return r;
+            return std::string(2*i,' ');
         }
 
         uint16_t unknownID_;  // 0xffff

src/bmffimage.cpp

@@ -67,10 +67,10 @@ struct BmffBoxHeader
 #define TAG_ispe 0x69737065 /**< "ispe" Image spatial extents */
 #define TAG_infe 0x696e6665 /**< "infe" Item Info Extention */
 #define TAG_ipma 0x69706d61 /**< "ipma" Item Property Association */
-#define TAG_cmt1 0x434d5431 /**< ifd0Id */
-#define TAG_cmt2 0x434D5432 /**< exifID */
-#define TAG_cmt3 0x434D5433 /**< canonID */
-#define TAG_cmt4 0x434D5434 /**< gpsID */
+#define TAG_cmt1 0x434d5431 /**< "CMT1" ifd0Id */
+#define TAG_cmt2 0x434D5432 /**< "CMD2" exifID */
+#define TAG_cmt3 0x434D5433 /**< "CMT3" canonID */
+#define TAG_cmt4 0x434D5434 /**< "CMT4" gpsID */
 
 // *****************************************************************************
 // class member definitions
@@ -88,9 +88,8 @@ namespace Exiv2
         return enable;
     }
 
-    class Iloc
+    struct Iloc
     {
-    public:
         Iloc(uint32_t ID = 0, uint32_t start = 0, uint32_t length = 0) : ID_(ID), start_(start), length_(length){};
         virtual ~Iloc(){};
 
@@ -215,7 +214,9 @@ namespace Exiv2
                 result = (long)io_->size();
                 box.length = result - address;
             }
+#ifdef EXIV2_DEBUG_MESSAGES
             std::cerr << Internal::stringFormat(" (%lu)", result);
+#endif
         }
 
         // read data in box and restore file position