Two principles of CMake you have to keep in mind: CMake is a script language and arguments are evaluated after the variables are expanded CMake differentiates between normal strings and list variables (strings with semicolon delimiters) Examples set(_my_text “A B C”) with message(“${_my_text}”) would give A B C set(_my_list A B C) with message(“${_my_list}”) would … Read more
gcc -E file.c or g++ -E file.cpp will do this for you. The -E switch forces the compiler to stop after the preprocessing phase, spitting all it’s got at the moment to standard output. Note: Surely you must have some #include directives. The included files get preprocessed, too, so you might get lots of output. … Read more
This behavior is underspecified but intended, though it might appear confusing. We plan to elaborate on the role of return type in macro signatures, but at the moment I feel like the flexibility is a good thing to have. Also at times the behavior is inconsistent, e.g. when the macro is caught in the middle … Read more
I’ve done a screenshot to show where it is in Xcode, because it’s easier 🙂 Select project file Select the target you want Go to Build Settings Search for ‘preprocessor’ Add your preprocessor macro either for Debug, Release, or both.
I am working on a large project that involves a lot of preprocessor macro functions to synthesize any code that cannot be replaced by templates. Believe me, I am familiar with all sorts of template tricks, but as long as there is no standardized, type safe metaprogramming language that can directly create code, we will … Read more
Here’s a relatively dumb example, but it does have a different result: #define Streq(s1, s2) (strcmp((s1), (s2)) == 0) #define MyStreq(s1, s2) (strcmp(s1, s2) == 0) #define s1 “foo”, “blah” int main() { Streq(s1, “blah”); // Compiles and compares equal. MyStreq(s1, “blah”); // Compiler error. Too many parameters. }
Macros don’t respect scoping rules and operate at the textual level, as opposed to the syntax level. From this arise a number of pitfalls that can lead to strange, difficult to isolate bugs. Consider the following well-known example: #define max(a, b) ((a) < (b) ? (b) : (a)) ⋮ int i = max(i++, j++); The … Read more
(The standard disclaimer about not abusing the C preprocessor without a really good reason applies here.) It’s certainly possible to do what you want to do. You need a STRINGIFY macro and a bit of macro indirection. Typically, STRINGIFY is defined with one level of indirection, to allow the C preprocessor to expand its arguments … Read more
Use () to stop the preprocessor from expanding the function definition: #include <stdio.h> #define myfunc(a, b) myfunc(do_a(a), do_b(b)) /* if you have a preprocessor that may be non-standard * and enter a loop for the previous definition, define * myfunc with an extra set of parenthesis: #define myfunc(a, b) (myfunc)(do_a(a), do_b(b)) ******** */ int (myfunc)(int … Read more
You can use various recursive macro techniques to do things with variadic macros. For example, you can define a NUM_ARGS macro that counts the number of arguments to a variadic macro: #define _NUM_ARGS(X100, X99, X98, X97, X96, X95, X94, X93, X92, X91, X90, X89, X88, X87, X86, X85, X84, X83, X82, X81, X80, X79, X78, … Read more