tony@yes:~/code/file/act1$ make
g++ -ggdb  -c lab6-1.cpp
g++ -ggdb  -c Block.cpp
g++ -ggdb  -c Display.cpp
g++ -ggdb  -c Figure.cpp
g++ -ggdb  -c TextString.cpp
g++ -ggdb  -c Triangle.cpp
g++ -ggdb -o file-1 file-1.o Block.o Display.o Figure.o TextString.o Triangle.o
file-1.o: In function `~Block':
/home/stu2/s7/tony/code/file/act1/Block.h:33: undefined reference to `vtable for Block'
Block.o: In function `Block':
/home/stu2/s7/tony/code/file/act1/Block.cpp:7: undefined reference to `vtable for Block'
/home/stu2/s7/tony/code/file/act1/Block.cpp:7: undefined reference to `vtable for Block'
collect2: ld returned 1 exit status
make: *** [file-1] Error 1