1. Compilation and Debugging
Andy Wang
Object Oriented Programming in C++
COP 3330

2. Multiple File Projects
For small programs, everything can fit in one file
For large programs, need to use separate files to organize code
A class typically consists of a pair of files
A header file (.h) that contains the class declaration
An implementation file (.cpp) that defines and implements the class member functions

3. File Names Do not need to match the class name
For a class, you can name the header file <className>.h and the implementation file <className>.cpp
circle.h // header file for a class called Circle
circle.cpp
The main program is usually written in a separate file

4. Compilation Two major stages Compile stage Checks syntax and types
Matches member function calls with their declarations in the header files
No need to know the definitions of member functions yet
Translates source code (.cpp files) into temporary object code (machine code .o files), not an executable program
Not to be confused with the “object” used in object oriented programming

5. Compilation Two major stages Linking stage
Links object code into an executable program
May involve one or more object code files
Makes sure that all member functions are implemented, with no duplications
The end of result of linking is usually an executable program

6. To Create a Multi-file Project
One possible organization
Essentially combines two files into one
NOT a good idea
// frac declaration
// frac definition
#include “frac.cpp”
// main function
frac.cpp
main.cpp

7. Separate Compiling and Linking
A better organization
Benefits
Change to a file requires recompiling only that file
Along with the linking
// frac declaration
frac.h
#include “frac.h”
// frac definition
#include “frac.h”
// main function
frac.cpp
main.cpp

8. Rule of Thumb
Only #include the header files
Not the .cpp files!

9. Example g++ Commands Translates frac.cpp into frac.o
g++ -c frac.cpp
Translates main.cpp into main.o
g++ -c main.cpp
Links .o files into an executable file called frac
g++ frac.o main.o –o frac

10. Makefiles The make utility eases the process of compilation
Puts various compilation commands into either a Makefile or makefile
To compile, just type make

11. The Makefile Format Consists of many sections The basic format
<target_name>: <dependency list>
<commands>
<target_name> depends on the items in the <dependency list>
To create <target_name>, run <commands>
If anything is changed in the <dependency list>, make will automatically rerun <commands>
<commands> refers to Unix commands
Each command must be preceded by a single tab

12. Example Makefile
# This is a comment line frac: main.o frac.o g++ main.o frac.o –o frac main.o: main.cpp frac.h g++ -c main.cpp frac.o: frac.cpp frac.h g++ -c frac.cpp clean: rm *.o frac

13. To Compile Type make make clean
make attempts to build the first target name in the Makefile
In this case, make is the same as make frac
make clean
Defined in the last section of Makefile
Will remove the .o files and the executable from the directory

14. Types of Errors Compilation errors Linker errors Runtime errors
Syntax errors
Undeclared variables and functions
Improper function calls
Linker errors
Undefined functions
Functions defined multiple times
Runtime errors
Crashes
Erroneous results

15. Types of Errors
Compilation and linker errors result in failed compilation
Runtime errors occur while the program is running
After successful compilation

16. Debugging Compilation errors Reported by the compiler Tips
Usually with a file name and a line number
Tips
Always start with the first reported error
If the list is long, compile and debug one file at a time
An error may be caused by the line prior to the line number reported
E.g., missing ‘;’
Compile and debug each function as you go
Don’t wait until after the entire file is written to compile it

17. Debugging Linking stage errors Usually do not report line numbers Tips
Undefined functions may result from forgetting to include a header file
Functions defined multiple times may mean name collisions

18. Example Compilation Errors
Missing ‘”’ or ‘;’
Mismatching declarations and definitions
Missing class scope information
Missing declarations
Broken comments
Wrong return type
Missing class variable when invoking member functions

19. Example Compilation Errors
Wrong syntax
‘,’ instead of ‘;’
Passing the wrong number of parameters
Duplicate definitions

20. Runtime Errors Must be tested while running a fully-compiled program
Tips
For a crash
Add printout statements to find the location prior to crash
#include <iostream>
using namespace std;
cout << __FILE__ << “:“ << __LINE__ << endl;
For logic errors
Print out internal variables to locate computation problems
Remember to remove print statements used for debugging in the submitted version