assert_invariants( self ); 
void string_push_back( string* self, char x ){    assert_invariants( self );    string_append_range( self, &x, &x + 1 );    assert_invariants( self );}
2658	/local/tlutelli/issta_data/temp/c/2005_temp/2005/2658/de59a71012c6325adb40e6770bd1647db934536c/strings.c/buggy/jam_src/strings.c