Compare ((char *)p)[0] against '\0', not (char *)p.

Also make the library example compile again under MSVC, and make the
perl scripts to build the image tables work.

Makefile.msvc

@@ -101,7 +101,8 @@ all: $(OBJDIR)\solvespace.exe
 	@echo solvespace.exe
 
 clean:
-	-rmdir /s /q $(OBJDIR)
+	-del /Q obj\*
+	-rmdir $(OBJDIR)
 
 $(OBJDIR)\solvespace.exe: $(SSOBJS) $(SRFOBJS) $(W32OBJS) $(RES)
 	$(CXX) $(DEFINES) $(CXXFLAGS) /Fe$(OBJDIR)\solvespace.exe $(SSOBJS) $(SRFOBJS) $(W32OBJS) $(RES) $(LIBS)
@@ -132,10 +133,10 @@ $(OBJDIR)\toolbar.obj: src\icons.h
 !IFDEF PERL
 
 src\icons.h: src\icons\*.png src\png2c.pl
-	$(PERL) src\png2c.pl $@ src\icons-proto.h
+	$(PERL) src\png2c.pl $@ src\icons-proto.h src
 
 src\bitmapextra.table.h: src\icons\*.png src\pngchar2c.pl
-	$(PERL) src\pngchar2c.pl >$@.tmp
+	$(PERL) src\pngchar2c.pl src >$@.tmp
 	move /y $@.tmp $@
 
 !ELSE IF EXIST(src\built)

exposed/lib.cpp

@@ -25,6 +25,7 @@ void CnfFreezeInt(uint32_t v, const char *name)
 uint32_t CnfThawInt(uint32_t v, const char *name)
 {
     abort();
+    return 0;
 }
 
 void DoMessageBox(const char *str, int rows, int cols, bool error)

src/file.cpp

@@ -220,10 +220,10 @@ void SolveSpace::SaveUsingTable(int type) {
         int fmt = SAVED[i].fmt;
         union SAVEDptr *p = (union SAVEDptr *)SAVED[i].ptr;
         // Any items that aren't specified are assumed to be zero
-        if(fmt == 'N' && p->N.str == '\0')   continue;
-        if(fmt == 'd' && p->d == 0)          continue;
-        if(fmt == 'f' && EXACT(p->f == 0.0)) continue;
-        if(fmt == 'x' && p->x == 0)          continue;
+        if(fmt == 'N' && p->N.str[0] == '\0')   continue;
+        if(fmt == 'd' && p->d == 0)             continue;
+        if(fmt == 'f' && EXACT(p->f == 0.0))    continue;
+        if(fmt == 'x' && p->x == 0)             continue;
 
         fprintf(fh, "%s=", SAVED[i].desc);
         switch(fmt) {