-#define O_FORMAT_GIF_STR "gif"
-#define O_FORMAT_PNG_STR "png"
-#define O_FORMAT_PNG16_STR "png16"
-#define O_FORMAT_PGM_STR "pgm"
-#define O_FORMAT_PGMASC_STR "pgmasc"
-#define O_FORMAT_DISP_STR "disp"
+static const char O_FORMAT_GIF_STR[]="gif";
+static const char O_FORMAT_PNG_STR[]="png" ;
+static const char O_FORMAT_PNG16_STR[]="png16" ;
+static const char O_FORMAT_PGM_STR[]="pgm";
+static const char O_FORMAT_PGMASC_STR[]="pgmasc";
+static const char O_FORMAT_DISP_STR[]="disp";