CMPT 212 Object-Oriented Applications Design in C++ Spring 1998

Dependencies (continued)

• When we build a program, we compile every source file then link the object files together to produce an executable file.
  • In the example above, we would compile one.cpp, two.cpp, and three.cpp, then link one.obj, two.obj, and three.obj to produce program.exe.

• When we make a program, we only compile the source files which have changed or which depend on files which have changed. If any object files have changed (either before the make or during the make), we link the object files to produce the executable file.
  • In the example above, if we changed two.cpp and then did a make, we would compile two.cpp then link one.obj, two.obj, and three.obj to produce program.exe.

  • If we changed three.h, we would compile two.cpp and three.cpp then link all of the object files.

  • If we changed two.obj, we would just link all the object files.

• Question: how do we tell if a file has been changed?
  • Normally we use the "last changed" time stamp of the file.

  • If file X depends on file Y and the time stamp of Y is later than the time stamp of X, then we assume that X must be reprocessed.

Comments in Header Files

• Function prototypes in header files should be commented with detailed descriptions about what the function does and about its parameters.
  • Everything that a programmer needs to know about using a function should be described here.

  • You should describe what a function does. How a function does it should be described with the function definition.

  • Other programmers should be able to take the object file and the header file of your module and use your module successfully.

Preventing Multiple Header File Inclusion

• A header file can include another header file.

• Example: one.h contains a definition of a data type that is used in two.h. When one.cpp (or two.cpp) is compiled, one.h is included twice.

• If the header file only contains function prototypes, it can safely be included more than once. But type or class definitions cannot appear more than once.

• Solution: use #ifndef and #define preprocessor directives.
  • The #define directive defines a value for the preprocessor.

  • The #ifndef directive causes the preprocessor to allow the compiler to compile a section of code only if a value has not been defined. (There is also a #ifdef directive.)

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