From 70106fd5e0540300d2262caa8df546828cab9825 Mon Sep 17 00:00:00 2001 From: Paul Buetow Date: Sat, 1 May 2021 18:36:52 +0100 Subject: add methods in c post --- content/html/gemfeed/2016-11-20-methods-in-c.html | 82 +++++++++++++++++++++++ 1 file changed, 82 insertions(+) create mode 100644 content/html/gemfeed/2016-11-20-methods-in-c.html (limited to 'content/html/gemfeed/2016-11-20-methods-in-c.html') diff --git a/content/html/gemfeed/2016-11-20-methods-in-c.html b/content/html/gemfeed/2016-11-20-methods-in-c.html new file mode 100644 index 00000000..5de22d33 --- /dev/null +++ b/content/html/gemfeed/2016-11-20-methods-in-c.html @@ -0,0 +1,82 @@ + + + +buetow.org - Having fun with computers! + + + + + +

Written by Paul Buetow 2016-11-20

Methods in C

You can do some sort of object oriented programming in the C Programming Language. However, that is very limited. But also very easy and straight forward to use.

Example

Lets take a look at the following sample program. Basically all you have to do is to add a function pointer such as "calculate" to the definition of struct "something_s". Later, during the struct initialization, assign a function address to that function pointer:

+#include 
+
+typedef struct {
+    double (*calculate)(const double, const double);
+    char *name;
+} something_s;
+
+double multiplication(const double a, const double b) {
+    return a * b;
+}
+
+double division(const double a, const double b) {
+    return a / b;
+}
+
+int main(void) {
+    something_s mult = (something_s) {
+        .calculate = multiplication,
+        .name = "Multiplication"
+    };
+
+    something_s div = (something_s) {
+        .calculate = division,
+        .name = "Division"
+    };
+
+    const double a = 3, b = 2;
+
+    printf("%s(%f, %f) => %f\n", mult.name, a, b, mult.calculate(a,b));
+    printf("%s(%f, %f) => %f\n", div.name, a, b, div.calculate(a,b));
+}
+

As you can see you can call the function (pointed by the function pointer) the same way as in C++ or Java via:

+printf("%s(%f, %f) => %f\n", mult.name, a, b, mult.calculate(a,b));
+printf("%s(%f, %f) => %f\n", div.name, a, b, div.calculate(a,b));
+

However, that's just syntactic sugar for:

+printf("%s(%f, %f) => %f\n", mult.name, a, b, (*mult.calculate)(a,b));
+printf("%s(%f, %f) => %f\n", div.name, a, b, (*div.calculate)(a,b));
+

Output:

+pbuetow ~/git/blog/source [38268]% gcc methods-in-c.c -o methods-in-c
+pbuetow ~/git/blog/source [38269]% ./methods-in-c
+Multiplication(3.000000, 2.000000) => 6.000000
+Division(3.000000, 2.000000) => 1.500000
+

Not complicated at all, but nice to know and helps to make the code easier to read!

Taking it further

If you want to get a bit further type "Object-Oriented Programming with ANSI-C" into your favourite internet search engine, you will find some crazy stuff. Some go as far as writing a C preprocessor in AWK, which takes some object oriented pseudo-C and transforms it to plain C so that the C compiler can compile it to machine code. This is actually similar to how the C++ language had its origins.

E-Mail me your throughts at comments@mx.buetow.org!

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