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The Makefile utility

The Makefile utility. COP 3402 (Fall 2014). Motivation. Small programs single file. “ Not so small ” programs: Many lines of code. Multiple components. More than one programmer. Motivation – continued. Problems : Long files are harder to manage

ethan-floyd
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The Makefile utility

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  1. The Makefile utility COP 3402 (Fall 2014)

  2. Motivation • Small programs single file. • “Not so small”programs: • Many lines of code. • Multiple components. • More than one programmer.

  3. Motivation – continued • Problems: • Long files are harder to manage (for both programmers and machines)‏. • Every change requires long compilation. • Many programmers can not modify the same file simultaneously. • Division to components is desired.

  4. Motivation – continued • Solution : divide project to multiple files. • Targets: • Good division to components. • Minimum compilation when something is changed. • Easy maintenance of project structure, dependencies and creation.

  5. Project maintenance • Done in Unix by the Makefilemechanism. • A makefile is a file (script) containing: • Project structure (files, dependencies).‏ • Instructions for files creation. • The make command reads a makefile, understands the project structure and creates the executable. • Note that the Makefile mechanism is not limited to C programs.

  6. Project structure • Project structure and dependencies can be represented as a DAG(Directed Acyclic Graph). • Example: • Program contains 3 files: • main.c., sum.c, sum.h • sum.h included in both .c files. • Executable should be the file sum.

  7. sum (exe)‏ sum.o main.o main.c sum.h sum.c sum.h Project structure

  8. makefile sum: main.osum.o gcc –o sum main.osum.o main.o: main.csum.h gcc –c main.c sum.o: sum.csum.h gcc –c sum.c

  9. Rule syntax main.o: main.csum.h gcc –c main.c Rule target action dependency

  10. Equivalent makefiles • .o depends (by default) on corresponding .c file. Therefore, an equivalent makefile is: sum: main.osum.o gcc –o sum main.osum.o main.o: sum.h gcc –c main.c sum.o: sum.h gcc –c sum.c

  11. make operation • Project dependencies tree is constructed. • Target of first rule should be created. • We go down the tree to see if there is a target that should be recreated. This is the case when the target file is older than one of its dependencies. • In this case we recreate the target file according to the action specified, on our way up the tree. Consequently, more files may need to be recreated. • If something is changed, linking is usually necessary.

  12. make operation - continued • make operation ensures minimum compilation, when the project structure is written properly. • Do not writesomething like: prog: main.c sum1.c sum2.c gcc –o progmain.c sum1.c sum2.c which requires compilation of the full projectwhen something is changed.

  13. Make operation - example FileLast Modified sum 10:03 main.o 09:56 sum.o09:35 main.c10:45 sum.c09:14 sum.h08:39

  14. Make operation - example • Operations performed: gcc –c main.c gcc –o sum main.osum.o • main.o should be recompiled (main.c is newer). • Consequently, main.o is newer than sum and therefore sum should be recreated (by re-linking).

  15. Reference • Good tutorial for makefiles: http://www.gnu.org/software/make/manual/make.html

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