made wxFFile a bit more safe: don't crash when Tell() and Length() are called on closed file (patch 811425)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@25566 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/ffile.h

@@ -86,7 +86,8 @@ public:
     // get current file length
   size_t Length() const;
 
-  // simple accessors
+  // simple accessors: note that Eof() and Error() may only be called if
+  // IsOpened()!
     // is file opened?
   bool IsOpened() const { return m_fp != NULL; }
     // is end of file reached?

src/common/ffile.cpp

@@ -206,6 +206,9 @@ bool wxFFile::Seek(long ofs, wxSeekMode mode)
 
 size_t wxFFile::Tell() const
 {
+    wxCHECK_MSG( IsOpened(), (size_t)-1,
+                 _T("wxFFile::Tell(): file is closed!") );
+
     long rc = ftell(m_fp);
     if ( rc == -1 )
     {
@@ -218,6 +221,9 @@ size_t wxFFile::Tell() const
 
 size_t wxFFile::Length() const
 {
+    wxCHECK_MSG( IsOpened(), (size_t)-1,
+                 _T("wxFFile::Length(): file is closed!") );
+
     wxFFile& self = *(wxFFile *)this;   // const_cast
 
     size_t posOld = Tell();