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For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Encapsulating logic in functions and structs - the C approach to Object Oriented techniques

Although C is not what is described as an "Object Oriented Language", many of the good programming principles that are applied naturally in OO programming can be applied in C too.

I wrote an example that showed this yesterday - with a C struct defining what is in essence an object, and being referenced through (and only through) functions. Complex logic, then, encapsulated with the functions, good and thorough test points being available, detailed functional code to access the data being easily re-usable in other programs.

Here's my initial main (test, customer-facing) program:

  int main(int argc, char ** argv) {
    visit * today ;
    int nVisits;
    int matched;
    printf("Testing / running program %s\n",*argv);
    /* open and read file via a factory */
    nVisits = loadVisits(&today,"ac_20160128");
    printf("Today is at %d\n",today);
    /* count up accesses to the home page */
    matched = countVisits("/mouth/3592_",today,nVisits);
    printf("Matched %d of %d\n",matched,nVisits);
    return 0;

and it's a good starting structure - you can't see how the data is handled it's checked and secure within the strucures passed to each function. One slight issue though - my separate int count which is passed back from my loader and passed in to subsequent calls - a potential weakness. I should also check the return status of my loader ... here's modified 'main' code with the changes:

  int test_03(int argc, char ** argv) {
    visit * today ;
    int nVisits;
    int matched;
    printf("Testing / running program %s\n",*argv);
   /* open and read file via a factory */
    if (loadVisits(&today,"ac_20160128")) {
      /* count up accesses to the home page */
      /* Now with a regular expression */
      matched = countVisits("[[:space:]]/index\\.html",today);
      /* count up total accesses */
      nVisits = countVisits(NULL,today);
      printf("Matched %d of %d\n",matched,nVisits);
      return 0;
    } else {
      fprintf(stderr,"Input file not avaulable\n");
      return 1;

Internally, I used malloc and realloc to provide memory and I needn't bother the user with the detail ;-) ... but if you want to take a look, source code as I build up is [here], [here], [here] and [here].

You'll note that "main" has been changed to "test_03" in my final example above. That's because I've built it into a test framework so that - over time - lots of tests can be built up and all run together. So that a change to something in the code base can be checked for "ripple effect" - in other words it can hep you check that fixing one bug hasn't given rise to another. All pretty important stuff as your system grows! See [here] for the article describing the test framework.
(written 2016-01-30, updated 2016-01-31)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
C221 - C and C based languages - Secure C Programming
C212 - C and C based languages - Memory Management
  [1497] Training Season Starts again! - (2008-01-07)
  [1581] What is an lvalue? (Perl, C) - (2008-03-18)
  [1589] Dynamic Memory Allocation in C - calloc, realloc - (2008-03-22)
  [1670] Dynamic Memory Allocation in C - (2008-06-09)
  [1845] Passing a table from Lua into C - (2008-10-18)
  [2669] Efficient use of dynamic memory - C and realloc - (2010-03-10)
  [2848] C course - final course example puts it all together - (2010-07-02)
  [3118] Arrays of arrays - or 2D arrays. How to program tables. - (2011-01-02)
  [3144] Setting up arrays in C - fixed size at compile time, or dynamic - (2011-01-24)
  [3386] Adding the pieces together to make a complete language - C - (2011-08-11)
  [3416] Storing Tcl source code encoded, and running via your own C program - (2011-09-02)
  [4128] Allocating memory dynamically in a static language like C - (2013-06-30)
  [4340] Simple C structs - building up to full, dynamic example - (2014-12-03)
  [4634] Regression testing - via a very short C testing framework - (2016-01-29)

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Rail user groups worried about what is happening on the buses
Encapsulating logic in functions and structs - the C approach to Object Oriented techniques
String handling in C - new examples of extracting integers from a string
Remember to ask the question before you listen for the answer
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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.

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