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Introduction to Programming3D ApplicationsCE00056-1 Lecture 6 Compiler options and makefiles
Compilation Factors • Small programs single file • “Not so small” programs : • Many lines of code • Multiple components • More than one programmer
Compilation Factors • 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
Compilation Factors • Divide project to multiple files • Good division to components • Minimum compilation when something is changed • Easy maintenance of project structure, dependencies and creation • Compiler directives used to refer to external files • Compilation can link several files together to create single application from several files • Can compile several source files, link to pre-compiled object files or combination of these options
C Preprocessor • Runs on a source code file before it gets to the compiler • Gets the source into compilable form • Strips out comments • Loads in header files • Replaces constant names with their values • Expands macros • Can chop out unneeded sections of code
C Preprocessor • Has its own very simple language • Three main kinds of statements: • #include • #define • conditionals (#ifdef, #ifndef, #if, #else, #elif, #endif)
Header Files and #include • Syntax: #include <library name.h> • Syntax: #include “header file.h” • Angle brackets used for shared, standard libraries (string.h, stdlib.h) • Double-quotes used for header files you have written yourself
Header Files & #include • Syntax: #include “header file.h” • #include works by essentially copying & pasting all the contents of the header file into your program • So whatever you put into a header file will then be present in your actual source code file
Header Files – Multiple use • Many source code files can all share the same header file • Useful for reusing code
Header Files • To make program work, need to be able to use the functions in one source code file in the other source code files • Header files enable this • Typically: one header file matched with each source code file • Header file contains the information that the *other* source code files need to use the functions in the matching source code file
Header File Contents cont. • If you put the prototype for a function into a header file, all the code in the files that #include that header file will be able to use that function. • Example: • input.c has a function int getInt() defined • prog.c has the main() function, which needs to use getInt() • put the prototype into input.h, and add the line #include “input.h” to both input.c and prog.c!
Header File Contents • What is necessary for one function to call another function? • The second function must have been declared previously – eg, via a function prototype • Remember – function does not have to be defined until later – in fact, not until the linking step
Breaking Up Programs • Up to now: one source code file (.c suffix) per program • But can have multiple source code files and also header files for one program • Each source code file gets compiled into an object file (.o suffix) separately • Multiple object files can be linked together to make a single executable
Multiple Source Code Files • IMPORTANT: only ONE source code file per program can have a main() routine! • Other source code files just have other functions • Typically, put all the functions that are related thematically into one separate source code file • eg, all functions that get user input might go into a file called “input.c” • Prototypes referring to the functions go in input.h
Compiling multiple-file programs • Problem: if you try to do this: • ‘cc –o input input.c’ • Error! No main function defined • Have to make the intermediate stage only: • ‘cc –c -o input.o input.c’
Compiling multiple-file programs • Problem: if you try to do this: • ‘cc –o prog prog.c’ • Error! No getInt() function defined • Even though input.h is included in prog.c • Have to first compile intermediate stage: • ‘cc –c -o prog.o prog.c’
Compiling multiple-file programs • Next, need to compile together input.o and prog.o into one executable file: • cc –o prog prog.o input.o • Produces one executable (named “prog”) out of the two separate object files • Can then run prog • A better way to compile several programs in this way is to provide a utility to compile and link in one go
Compiling multiple-file programs • Done in Unix by the Makefile mechanism • 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 makes up the executable • Note that the Makefile mechanism is not limited to C programs
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
make operation - continued • make operation ensures minimum compilation, when the project structure is written properly • Do not write something like: prog: main.c sum1.c sum2.c cc –o prog main.c sum1.c sum2.c which requires compilation of all project when something is changed
Makefile example • Consider, previous example program contained in two separate source files. • “prog.c” • “input.c” • Both contain header “input.h” • Require executable file to be named “prog” • Next slide shows a simple makefile that could be used.
Comment line preceded with “#” “Dependency line” “Action line” Dependency line + Action line = “Rule” Action line must begin with a tab character Dependency line must start in column 1 Makefile example # Make file for prog executable prog: input.o prog.o cc –o prog input.o prog.o prog.o: prog.c input.h cc –c –o prog.o prog.c input.o: input.c input.h cc –c –o input.o input.c
Makefile example # Make file for prog executable prog: input.o prog.o cc –o prog input.o prog.o prog.o: prog.c input.h cc –c prog.c input.o: input.c input.h cc –c input.c Note –o ????.o not really required because it is default output