He currently resides in the Washington, DC area. He is an alumnus of the University of Wisconsin-Milwaukee and the Université d'Orléans. Mike Ash is a programmer at Plausible Labs by night, and a glider pilot by day. Tricks can help you create macros which make your code easier to write However, in some situations theyĬan be incredibly useful, and, when used correctly, these tips and If you use them, you must beĮxtremely careful not to abuse them. More information about X-macros, consult the Wikipedia article.Ĭ macros are complicated and powerful. This is an advanced and frightening technique, but it could helpĮliminate a lot of boring repetition in certain specialized cases. make the compiler treat x as the given type no matter what #define FORCETYPE(x, type) *(type *)(_typeof_(x) ) It's common to write a macro that consists of multiple statements. How the code has gone wrong, then modify your macro to make it right. Find the site where the macro is used, figure out The resulting file will generally be very largeĭue to all of the #include directives, but you'll find yourĬode near the end. In Xcode you can do this by selectingīuild->Preprocess. During the preprocessing stage, the C preprocessor (a part of the C compiler) simply substitutes the body of the macro wherever its name appears. This means all of your macros are expanded, and youĬan see the raw C code that the compiler sees, rather than trying toĮxpand the macro in your head. A C macro is just a preprocessor command that is defined using the definepreprocessor directive. To reduce confusion, you'll want to look at the file as it appearsĪfter preprocessing. To manifest as weird compiler errors at the site where the macro is Macros are code, and like any code, they will have bugs. Syntax for calling a function, but don't be fooled. The syntax for using a parameterized macro looks just like the the Since it declares variables in the for loop header, it only works in C11 or later.#define MAX(x, y) ((x) > (y) ? (x) : (y)) int a = 0 int b = 1 int c = MAX ( a ++, b ++ ) // now a = 1, c = 1, and b = 3! // (a++ > b++ ? a++ : b++) // b++ gets evaluated twice.Relies on typeof(), which is a GNU extension, not part of standard C.Doesn't work for multi-dimensional arrays.Scope of the loop (since they're declared in the for loop header). All variables created in macro ( p, item), aren't visible outside the.Seems to work on any 1-dimensional array.item is declared and incremented within the for statement (just like.which can be used with for (as in for each (.)). As you probably already know, there's no "foreach"-style loop in C.Īlthough there are already tons of great macros provided here to work around this, maybe you'll find this macro useful: // "length" is the length of the array.
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