book

Head First C

by David Griffiths, Dawn Griffiths

April 2012

Intermediate to advanced

632 pages

13h 51m

English

O'Reilly Media, Inc.

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Head First C
Dedication
Advance Praise for Head First C
Praise for other Head First books
Authors of Head First C
How to use this Book: Intro
Who is this book for?Who should probably back away from this book?We know what you’re thinkingWe know what your brain is thinkingMetacognition: thinking about thinkingHere’s what WE didHere’s what YOU can do to bend your brain into submissionRead meThe technical review teamAcknowledgmentsSafari® Books Online
1. Getting Started with C: Diving in
C is a language for small, fast programsThe way C worksBut what does a complete C program look like?But how do you run the program?The program works!Two types of commandDo somethingDo something only if something is trueHere’s the code so farCard counting? In C?There’s more to booleans than equals...&& checks if two conditions are trueII checks if one of two conditions is true! flips the value of a conditionWhat’s the code like now?Pulling the ol’ switcherooSometimes once is not enough...Using while loops in CLoops often follow the same structure......and the for loop makes this easyYou use break to break out......and continue to continueYour C Toolbox
2. Memory and Pointers: What are you pointing at?
C code includes pointersDigging into memorySet sail with pointersSet sail sou’east, Cap’nTry passing a pointer to the variablePointers make it easier to share memoryUsing memory pointersHow do you pass a string to a function?Honey, who shrank the string?Array variables are like pointers......so our function was passed a pointerWhat the computer thinks when it runs your codeBut array variables aren’t quite pointersWhy arrays really start at 0Why pointers have typesUsing pointers for data entryEntering numbers with scanf()Be careful with scanf()scanf() can cause buffer overflowsfgets() is an alternative to scanf()Using sizeof with fgets()Anyone for three-card monte?Oops...there’s a memory problem...String literals can never be updatedIf you’re going to change a string, make a copyMemory memorizerYour C Toolbox
2.5. Strings: String theory
Desperately seeking Susan FrankCreate an array of arraysFind strings containing the search textUsing string.hUsing the strstr() functionIt’s time for a code reviewArray of arrays vs. array of pointersYour C Toolbox
3. Creating Small Tools: Do one thing and do it well
Small tools can solve big problemsHere’s how the program should workBut you’re not using files...You can use redirectionYou can redirect the Standard Input with <......and redirect the Standard Output with >But there’s a problem with some of the data...Introducing the Standard ErrorBy default, the Standard Error is sent to the displayfprintf() prints to a data streamLet’s update the code to use fprintf()Small tools are flexibleDon’t change the geo2json toolA different task needs a different toolConnect your input and output with a pipeThe bermuda toolBut what if you want to output to more than one file?Roll your own data streamsThe program runs, but...There’s more to main()Overheard at the Head First PizzeriaLet the library do the work for youYour C Toolbox

4. Using Multiple Source Files: Break it down, build it up
Don’t put something big into something smallUse casting to put floats into whole numbersOh no...it’s the out-of-work actors...Let’s see what’s happened to the codeCompilers don’t like surprisesFixing function order is a painIn some situations, there is no correct orderSplit the declaration from the definitionCreating your first header fileIf you have common features......it’s good to share codeYou can split the code into separate filesCompilation behind the scenesThe shared code needs its own header fileInclude encrypt.h in your programIt’s not rocket science...or is it?Don’t recompile every fileSave copies of the compiled codeFirst, compile the source into object filesThen, link them togetherIt’s hard to keep track of the filesAutomate your builds with the make toolWhat does make need to know?How make worksTell make about your code with a makefileYour C ToolboxC Lab 1: ArduinoThe spec: make your houseplant talkThe physical deviceThe ArduinoThe Arduino IDEBuild the physical deviceBuild the moisture sensorConnect the LEDConnect the moisture sensorHere’s what your code should doRead from the moisture sensorWrite to the LEDWrite to the serial portHere’s what your C code should look likeHere are some useful Arduino functionsThe finished product
5. Structs, Unions, and Bitfields: Roll your own structures
Sometimes you need to hand around a lot of dataCubicle conversationCreate your own structured data types with a structJust give them the fishRead a struct’s fields with the “.” operatorCan you put one struct inside another?How do you update a struct?The code is cloning the turtleYou need a pointer to the struct(*t).age vs. *t.ageSometimes the same type of thing needs different types of dataA union lets you reuse memory spaceHow do you use a union?C89 style for the first fieldDesignated initializers set other valuesSet the value with dot notationunions are often used with structsAn enum variable stores a symbolSometimes you want control at the bit levelBitfields store a custom number of bitsYour C Toolbox
6. Data Structures and Dynamic Memory: Building bridges
Do you need flexible storage?Linked lists are like chains of dataLinked lists allow insertsCreate a recursive structureCreate islands in C......and link them together to form a tourInserting values into the listUse the heap for dynamic storageFirst, get your memory with malloc()Give the memory back when you’re doneFree memory by calling the free() functionAsk for memory with malloc()......and free up the memory with free()Oh, no! It’s the out-of-work actors...Let’s fix the code using the strdup() functionSo does it fix the code?Free the memory when you’re doneExhibit A: the source codeAn overview of the SPIES systemThe program builds a tree of suspectsSoftware forensics: using valgrindPrepare your code: add debug infoJust the facts: interrogate your codeUse valgrind repeatedly to gather more evidenceThis time, valgrind found a memory leakLook at the evidence1. Location2. Clues from valgrindThe fix on trialThe leak is fixedYour C Toolbox
7. Advanced Functions: Turn your functions up to 11
Looking for Mr. Right...Pass code to a functionYou need to tell find() the name of a functionEvery function name is a pointer to the function......but there’s no function data typeWhy doesn’t C have a function data type?How to create function pointersGet it sorted with the C Standard LibraryUse function pointers to set the orderAutomating the Dear John lettersCreate an array of function pointersBut how does an array help?Make your functions streeeeeetchySo how can YOU do that?Your C Toolbox
8. Static and Dynamic Libraries: Hot-swappable code
Code you can take to the bankAngle brackets are for standard headersBut what if you want to share code?Sharing .h header filesShare .o object files by using the full pathnameAn archive contains .o filesCreate an archive with the ar command......then store the .a in a library directoryFinally, compile your other programsThe Head First Gym is going globalCalculating caloriesBut things are a bit more complex...Programs are made out of lots of pieces......but once they’re linked, you can’t change themDynamic linking happens at runtimeCan you link .a at runtime?Dynamic libraries are object files on steroidsFirst, create an object fileWhat you call your dynamic library depends on your platformCompiling the elliptical programYour C ToolboxC Lab 2: OpenCVThe spec: turn your computer into an intruder detectorThe intruder detectorOpenCVInstalling OpenCVWhat your code should doTake input from your computer cameraGrab an image from the webcamDetect an intruderMake a clean getawayOptional: show the current webcam outputThe finished productIt’s time to become a C ninja...
9. Processes and System Calls: Breaking boundaries
System calls are your hotline to the OSThen someone busted into the system...Security’s not the only problemThe exec() functions give you more controlexec() functions replace the current processThere are many exec() functionsThe list functions: execl(), execlp(), execle()The array functions: execv(), execvp(), execve()Passing environment variablesBut what if there’s a problem?Most system calls go wrong in the same wayRead the news with RSSexec() is the end of the line for your programfork() will clone your processRunning a child process with fork() + exec()1. Make a copy2. If you’re the child process, call exec()Your C Toolbox
10. Interprocess Communication: It’s good to talk
Redirecting input and outputA look inside a typical processRedirection just replaces data streamsProcesses can redirect themselvesfileno() tells you the descriptordup2() duplicates data streamsSometimes you need to wait...The waitpid() functionStay in touch with your childReading story links from rssgossipConnect your processes with pipesPiped commands are parents and childrenCase study: opening stories in a browserpipe() opens two data streamsIn the childIn the parentOpening a web page in a browserThe death of a processThe O/S controls your program with signalsCatching signals and running your own codeA sigaction is a function wrapperAll handlers take signal argumentssigactions are registered with sigaction()Rewriting the code to use a signal handlerUse kill to send signalsSend signals with raise()Sending your code a wake-up call...the timer fires a SIGALRM signalYour C Toolbox
11. Sockets and Networking: There’s no place like 127.0.0.1
The Internet knock-knock serverKnock-knock server overviewBLAB: how servers talk to the Internet1. Bind to a port2. Listen3. Accept a connectionA socket’s not your typical data streamSometimes the server doesn’t start properlyWhy your mom always told you to check for errorsBound ports are stickyReading from the clientThe server can only talk to one person at a timeYou can fork() a process for each clientThe parent and child use different socketsWriting a web clientClients are in chargeRemote ports and IP addressesCreate a socket for an IP addressgetaddrinfo() gets addresses for domainsCreate a socket for a domain nameYour C Toolbox
12. Threads: It’s a parallel world
Tasks are sequential...or not......and processes are not always the answerSimple processes do one thing at a timeEmploy extra staff: use threadsHow do you create threads?Create threads with pthread_createThe code is not thread-safeYou need to add traffic signalsUse a mutex as a traffic signalYour C ToolboxC Lab 3: BlasteroidsWrite the arcade game BlasteroidsYour mission: blast the asteroids without getting hitAllegroInstalling AllegroYou may need CMakeWhat does Allegro do for you?Building the gameThe spaceshipWhat the spaceship looks likeCollisionsSpaceship behaviorReading keypressesThe blastBlast appearanceBlast behaviorThe asteroidAsteroid appearanceHow the asteroid movesWhen the asteroid is hit by a blastThe game statusUse transformations to move things aroundThe finished productLeaving town...It’s been great having you here in Cville!
A. Leftovers: The top ten things (we didn’t cover)
#1. OperatorsIncrements and decrementsThe ternary operatorBit twiddlingCommas to separate expressions#2. Preprocessor directivesConditions#3. The static keywordstatic can also make things private#4. How big stuff is#5. Automated testing#6. More on gccOptimizationWarnings#7. More on makeVariablesUsing %, ^, and @Implicit rules#8. Development toolsgdbgprofgcov#9. Creating GUIsLinux — GTKWindowsThe Mac — Carbon#10. Reference materialWebsites
B. C Topics: Revision roundup
BasicsPointers and memoryStringsData streamsData typesMultiple filesStructsUnions and bitfieldsData structuresDynamic memoryAdvanced functionsStatic and dynamic librariesProcesses and communicationSockets and networkingThreads
Index
About the Authors
Copyright

Content preview from Head First C

Chapter 11. Sockets and Networking: There’s no place like 127.0.0.1

Programs on different machines need to talk to each other.

You’ve learned how to use I/O to communicate with files and how processes on the same machine can communicate with each other. Now you’re going to reach out to the rest of the world, and learn how to write C programs that can talk to other programs across the network and across the world. By the end of this chapter, you’ll be able to create programs that behave as servers and programs that behave as clients.

The Internet knock-knock server

C is used to write most of the low-level networking code on the Internet. Most networked applications need two separate programs: a server and a client.

You’re going to build a server in C that tells jokes over the Internet. You’ll be able to start the server on one machine like this:

Other than telling you it’s running, the server won’t display anything else on the screen. However, if you open a second console, you’ll be able to connect to the server using a client program called telnet. Telnet takes two parameters: the address of the server, and the port the server is running on. If you are running telnet on the same machine as the server, you can use 127.0.0.1 for the address:

Watch it!

You’ll be using telnet quite a lot ...

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Head First C

by David Griffiths, Dawn Griffiths

Chapter 11. Sockets and Networking: There’s no place like 127.0.0.1