For 2023 - 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 Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own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)) |
C Structs - what, how and why
If you want to hold a whole series of different values about something in a C program, you'll define yourself a structure (or struct.). You give a type and name to each of the elements in the structure, and then you give an overall variable name to each instance of the struct that you create.
Here, for example, I am defining a type called "result" - to hold everything about the results of a test, for example:
typedef struct {
int lowlim;
int highlim;
int pass;
int range;
float dut_out;
} result;
So far, I have only defined a type .. not any actual variables that contain results; I can declare those in the way I normally declare variables, including defining pointers to them if I wish:
result *current
result first;
result second;
Elements within a structure variable can be referenced (set or read) using a "." notation - for example:
second.dut_out = 50.0;
printf("The range was %d\n",second.range);
If you want to reference elements within a referenced struct (such as current in our example) you COULD write:
(*current).range
but that gets messy and an alternative, bracket-free notation is available:
current->range
You'll use pointers to structs very commonly indeed - to pass them around between function, to define them dynamically with calloc and realloc, etc.
Full source code example, showing all the things I have mentioned above, [HERE].
(written 2010-01-13)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles C209 - C and C based languages - Structures and Unions [1478] Some new C programming examples - files, structs, unions etc - (2007-12-19) [1572] C - structs and unions, C++ classes and polymorphism - (2008-03-13) [1584] Using Structs and Unions together effectively in C - (2008-03-21) [1669] What are Unions (C programming) - (2008-06-08) [3122] When is a program complete? - (2011-01-06) [3145] Structures v Structure Pointers in C. How, which, why. - (2011-01-25) [3386] Adding the pieces together to make a complete language - C - (2011-08-11)
Some other Articles
Complete teaching example - C++, inheritance, polymorphismWhat does const mean? C and C++Sharing variables between files of code in C - externSummary of Wiltshire Core Strategy responsesC Structs - what, how and whyThe what and why of C pointersReading and writing files in CFunction Prototypes in CHow to run a successful online poll / petition / survey / consultationForums for your Melksham and open source discussions
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