Index: commandline.doc
==================================================================
--- commandline.doc
+++ commandline.doc
@@ -37,10 +37,13 @@
   Start in the editor instead of game.
 
 -n (not implemented yet)
   Create a new puzzle set.
 
+-r
+  Open in read-only mode.
+
 -t
   Enable tracing.
 
 -v
   More verbose error logging.

Index: main.c
==================================================================
--- main.c
+++ main.c
@@ -143,11 +143,11 @@
     if(us) *us=sqlite3_value_dup(sqlite3_column_value(readusercachest,6));
     if(sqlite3_column_type(readusercachest,5)==SQLITE_BLOB) {
       const unsigned char*con=sqlite3_column_blob(readusercachest,5);
       *sz=sqlite3_column_bytes(readusercachest,5);
       buf=malloc(*sz);
-      if(*sz && !buf) fatal("Allocation failed");
+      if(*sz && !buf) fatal("Allocation failed\n");
       memcpy(buf,con,*sz);
     } else {
       FILE*fp=sol?solutionfp:levelfp;
       rewind(fp);
       fseek(fp,sqlite3_column_int64(readusercachest,4)-4,SEEK_SET);
@@ -386,13 +386,15 @@
     fwrite(sqlite3_column_text(st,1),1,sqlite3_column_bytes(st,1)+1,fp);
     j=sqlite3_column_bytes(st,2);
     fputc(j>>16,fp); fputc(j>>24,fp); fputc(j,fp); fputc(j>>8,fp);
     ofs[i++]=ftell(fp);
     fwrite(sqlite3_column_blob(st,2),1,j,fp);
+    if(ferror(fp)) fatal("I/O error: %m\n");
   }
   if(e!=SQLITE_DONE) fatal("SQL error (%d): %s\n",e,sqlite3_errmsg(userdb));
   if(ftruncate(fd,ftell(fp))) fatal("I/O error: %m\n");
+  rewind(fp);
   sqlite3_finalize(st);
   if(e=sqlite3_prepare_v2(userdb,"UPDATE `USERCACHEDATA` SET `OFFSET` = ?2 WHERE `ID` = ?1;",-1,&st,0)) fatal("SQL error (%d): %s\n",e,sqlite3_errmsg(userdb));
   i=0;
   while(i<c) {
     sqlite3_reset(st);
@@ -438,12 +440,12 @@
   if(z=sqlite3_prepare_v2(userdb,"SELECT `ID`, `TIME` FROM `USERCACHEINDEX` WHERE `NAME` = ?1;",-1,&st,0)) fatal("SQL error (%d): %s\n",z,sqlite3_errmsg(userdb));
   nam1=sqlite3_mprintf("%s.level",basefilename);
   if(!nam1) fatal("Allocation failed\n");
   nam2=realpath(nam1,0);
   if(!nam2) fatal("Cannot find real path of '%s': %m\n",nam1);
-  levelfp=fopen(nam2,"r");
-  if(!levelfp) fatal("Cannot open '%s' for reading: %m\n",nam2);
+  levelfp=fopen(nam2,main_options['r']?"r":"r+");
+  if(!levelfp) fatal("Cannot open '%s' for reading%s: %m\n",nam2,main_options['r']?"":"/writing");
   sqlite3_free(nam1);
   sqlite3_bind_text(st,1,nam2,-1,0);
   z=sqlite3_step(st);
   if(z==SQLITE_ROW) {
     leveluc=sqlite3_column_int64(st,0);
@@ -457,12 +459,12 @@
   nam1=sqlite3_mprintf("%s.solution",basefilename);
   if(!nam1) fatal("Allocation failed\n");
   nam3=realpath(nam1,0);
   if(!nam3) fatal("Cannot find real path of '%s': %m\n",nam1);
   if(!strcmp(nam2,nam3)) fatal("Level and solution files seem to be the same file\n");
-  solutionfp=fopen(nam3,"r");
-  if(!solutionfp) fatal("Cannot open '%s' for reading: %m\n",nam3);
+  solutionfp=fopen(nam3,main_options['r']?"r":"r+");
+  if(!solutionfp) fatal("Cannot open '%s' for reading%s: %m\n",nam3,main_options['r']?"":"/writing");
   sqlite3_free(nam1);
   sqlite3_bind_text(st,1,nam3,-1,0);
   z=sqlite3_step(st);
   if(z==SQLITE_ROW) {
     solutionuc=sqlite3_column_int64(st,0);
@@ -475,11 +477,10 @@
   sqlite3_finalize(st);
   if(stat(nam2,&fst)) fatal("Unable to stat '%s': %m\n",nam2);
   if(!fst.st_size) fatal("File '%s' has zero size\n",nam2);
   if(fst.st_mtime>t1 || fst.st_ctime>t1) leveluc=reset_usercache(levelfp,nam2,&fst,".LVL");
   if(stat(nam3,&fst)) fatal("Unable to stat '%s': %m\n",nam3);
-  if(!fst.st_size) fatal("File '%s' has zero size\n",nam2);
   if(fst.st_mtime>t2 || fst.st_ctime>t2) solutionuc=reset_usercache(solutionfp,nam3,&fst,".SOL");
   free(nam2);
   free(nam3);
   if(z=sqlite3_prepare_v3(userdb,"SELECT * FROM `USERCACHEDATA` WHERE `FILE` = ?1 AND `LEVEL` = ?2;",-1,SQLITE_PREPARE_PERSISTENT,&readusercachest,0)) {
     fatal("SQL error (%d): %s\n",z,sqlite3_errmsg(userdb));