Home Accessibility Courses Twitter The Mouth Facebook Resources Site Map About Us Contact
Retiring, March 2020 - sorry, you have missed our final public course.
The Coronavirus situation has lead us to suspend public training - which was on the cards anyway, with no plans to resume

Please ask about private 'maintenance' training for Python, Tcl, Perl, PHP, Lua, etc
Happily continuing private consultancy / programming work
Function Prototypes in C

Programs other than the shortest are name up of named blocks of code (functions) into which parameters are passed and from which results are returned. And rather than have all the functions that make up an application in one file of source, you'll share them between several. That way, maintainable is in more manageable chunks, and you can use parts of your code in several programs by loading the same named blocks into a series of programs that share them.

But there's a bit of an "issue" with that, in that at the time you compile each of the individual files of functions (prior to loading them *all* together), you're in danger of calling a function with the wrong number and type of parameters, and to not be "picked up" on the error by the compiler either. If you've even seen "Segmentation fault - memory violation" messages from a program, there's a good chance that they were caused by an error of this type that wasn't checked. Kernighan and Ritchie, two of the originators of C, wrote the definitive text book on the language and this version of the language is known as "K&R C".

Under more recent C - "ANSI C" - there's a solution. At the top of each file of your C source, you should include a function prototype - a template, if you like - for each function that you'll call, so that the compiler CAN make its checks, and segmentation faults / segmentation violations can be largely pre-empted.

Here are some sample function prototypes:
  float gimme_table(float, int );
  void silly_message() ;

The gimme_table function takes two parameters - a float and an int, and returns a float. silly_message may or may not take parameters (use the word void in the brackets to say it never takes any parameters) and returns nothing.

So far so good ... but do you REALLY want to repeat all the function prototypes in every file of source - if you do, you have just created a maintenance problem. So you group them all together into a file which you load through a #include directive to your C preprocessor.

By default the ANSI C compiler will complain strongly about missing function prototypes ... so that you've now got a scheme in which you maintain a single file that lists all your functions, and which will tell you straight away at compile time if you've accidentally created some code which doesn't match what you have set up, rather than having to find out about it when debugging some obscure behavior much later on.

There's a complete example - all three files - on our web site; a new example written earlier today on the C Programming course

1. The main program

2. The functions that it uses

3. The file of function prototypes that's called in by both of the other two.

(written 2010-01-11, updated 2010-01-13)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
C203 - C and C based languages - Conditionals and Loops
  [4337] Learning to program sample program - past its prime, but still useful - (2014-12-02)
  [4323] Learning to program - Loop statements such as while - (2014-11-22)
  [4322] Learning to Program - the conditional statement (if) - (2014-11-21)
  [3397] Does a for loop evaluate its end condition once, or on every iteration? - (2011-08-18)
  [3384] Loops - a comparison of goto, while and for - (2011-08-10)
  [3243] Breaking the running sequence - an introduction to conditional statements and loops - (2011-04-11)
  [3200] How a for loop works Java, Perl and other languages - (2011-03-12)
  [3121] New year, new C Course - (2011-01-05)
  [3004] Increment operators for counting - Perl, PHP, C and others - (2010-10-18)
  [2002] New C Examples - pointers, realloc, structs and more - (2009-01-20)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [1582] Ruby, C, Java and more - getting out of loops - (2008-03-19)
  [1220] for loop - how it works (Perl, PHP, Java, C, etc) - (2007-06-06)
  [1191] Smart English Output - via PHP and Perl ? : operator - (2007-05-18)
  [962] Breaking a loop - Ruby and other languages - (2006-12-03)
  [353] Wimbledon Neck - (2005-06-20)

C204 - C and C based languages - Functions, Macros and programs in multiple files
  [4557] Function prototype - what they are and why you should use them - C and C++ - (2015-10-27)
  [4555] Preprocessor directives in C and C++ - what they mean - (2015-10-27)
  [4554] Passing information into functions in C - by name, by value - (2015-10-26)
  [4338] Passing arrays into functions in C - (2014-12-02)
  [3721] Naming blocks of code, structures and Object Orientation - efficient coding in manageable chunks - (2012-05-06)
  [3717] Returning extra results from a function in C - (2012-05-03)
  [3237] Using functions to keep look and feel apart from calculations - simple C example - (2011-04-09)
  [2841] C Course exercise and sample answer - source in 2 files - (2010-06-30)
  [2575] Sharing variables between files of code in C - extern - (2010-01-14)
  [1478] Some new C programming examples - files, structs, unions etc - (2007-12-19)
  [1163] A better alternative to cutting and pasting code - (2007-04-26)
  [775] Do not duplicate your code - (2006-06-23)

Back to
How to run a successful online poll / petition / survey / consultation
Previous and next
Horse's mouth home
Forward to
Reading and writing files in C
Some other Articles
Summary of Wiltshire Core Strategy responses
C Structs - what, how and why
The what and why of C pointers
Reading and writing files in C
Function Prototypes in C
How to run a successful online poll / petition / survey / consultation
Forums for your Melksham and open source discussions
Extra MySQL course dates (2 day course, UK)
Excellent staff make for excellent hotel
Bright day, snowy day
4759 posts, page by page
Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96 at 50 posts per page

This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

Link to Ezine home page (for reading).
Link to Blogging home page (to add comments).

You can Add a comment or ranking to this page

© WELL HOUSE CONSULTANTS LTD., 2020: 48 Spa Road • Melksham, Wiltshire • United Kingdom • SN12 7NY
PH: 01225 708225 • EMAIL: info@wellho.net • WEB: http://www.wellho.net • SKYPE: wellho

PAGE: http://www.wellho.net/mouth/2570_Fun ... -in-C.html • PAGE BUILT: Sat May 27 16:49:10 2017 • BUILD SYSTEM: WomanWithCat