variadic-macros

问题 In C, I'm used to having: if (ELEM(value, a, b, c)) { ... } which is a macro with a variable number of arguments to avoid typing out if (value == a || value == b || value == c) { ... } A C example can be seen in Varargs `ELEM` macro for use with C. Is this possible in Rust? I assume it would use match . If so, how would variadic arguments be used to achieve this? 回答1: macro_rules! cmp { // Hack for Rust v1.11 and prior. (@as_expr $e:expr) => { $e }; ($lhs:expr, $cmp:tt any $($rhss:expr),*) =>

问题 Using Paul Fultz II's solution in the post C-preprocessor recursive macro, I'd like to expand an unlimited number of parenthesized macro arguments, e.g. #define MY_CHAIN (alpha) (beta) (gamma) into a comma-separated list which can be passed to a variadic macro, e.g. CHAIN_COMMA(MY_CHAIN) // alpha, beta, gamma I'm able to expand into braces [alpha] [beta] [gamma] and delimit the list with everything I've tried except a comma, alpha :: beta :: gamma in the example below. Here is my full

问题 #define LOGI(...) ((void)__android_log_print(ANDROID_LOG_INFO, "native-activity", __VA_ARGS__)) #define LOGW(...) ((void)__android_log_print(ANDROID_LOG_WARN, "native-activity", __VA_ARGS__)) This is definition for these 2 macros; later in the code LOGI and LOGW are used this way LOGI("accelerometer: x=%f y=%f z=%f", event.acceleration.x, event.acceleration.y, event.acceleration.z); and this way LOGW("Unable to eglMakeCurrent"); Since I try to avoid complex macros and #define in general, I

问题 #define LOGI(...) ((void)__android_log_print(ANDROID_LOG_INFO, "native-activity", __VA_ARGS__)) #define LOGW(...) ((void)__android_log_print(ANDROID_LOG_WARN, "native-activity", __VA_ARGS__)) This is definition for these 2 macros; later in the code LOGI and LOGW are used this way LOGI("accelerometer: x=%f y=%f z=%f", event.acceleration.x, event.acceleration.y, event.acceleration.z); and this way LOGW("Unable to eglMakeCurrent"); Since I try to avoid complex macros and #define in general, I

问题 I have 2 wrapper macros for asserting function input parameters: /** * @brief An assert wrapper with no value return in case assert fails. * @param x_: value to test for being non zero. */ #define UTIL_ASSERT_VOID(x_) \ assert_param(x_); \ if (!x_) \ return; \ /** * @brief An assert wrapper with a value return in case assert fails. * @param x_: value to test for being non zero. */ #define UTIL_ASSERT_VAL(x_, ret_) \ assert_param(x_); \ if (!x_) \ return ret_; \ The former is used in functions

问题 I'm wondering if it's possible to "nest" variadic macro invocations. I'm only truly concerned with GCC and Clang. My macro definition looks like this: /** * @brief Invoke an instance method. */ #define $(obj, method, ...) \ ({ \ typeof(obj) _obj = obj; \ _obj->interface->method(_obj, ## __VA_ARGS__); \ }) I use this to conveniently call "instance methods" in my OO framework (https://github.com/jdolan/objectively): $(array, addObject, obj); Works boss. Unfortunately, I haven't yet figured out

问题 Consider the following code (live example): #define TEST_VA(mX, ...) TEST #define STRINGIFY_IMPL(mX) #mX #define STRINGIFY(mX) STRINGIFY_IMPL(mX) #include <iostream> int main() { std::cout << STRINGIFY(TEST_VA(1)) << std::endl; std::cout << STRINGIFY(TEST_VA()) << std::endl; return 0; } clang++ 3.4 complains: main.cpp:9:37: warning: must specify at least one argument for '...' parameter of variadic macro [-Wgnu-zero-variadic-macro-arguments] std::cout << STRINGIFY(TEST_VA(1)) << std::endl; ^

问题 I'm trying to overload a macro by the number of parameter. Of course I can't actually overload the macro. I've tried using variadic macros to choose the right macro (using the fact that if __VA_ARGS__ doesn't exist it's supposed to delete the last coma before it - GCC Reference ): #define TEST1() printf("TEST1"); #define TEST2() printf("TEST2"); #define CHOOSER(x, y,FUNC,...) FUNC() #define MANIMACRO(...) CHOOSER(,__VA_ARGS__,TEST1,TEST2) int main(void) { MANIMACRO(1); MANIMACRO(); } The idea

问题 I'm trying to overload a macro by the number of parameter. Of course I can't actually overload the macro. I've tried using variadic macros to choose the right macro (using the fact that if __VA_ARGS__ doesn't exist it's supposed to delete the last coma before it - GCC Reference ): #define TEST1() printf("TEST1"); #define TEST2() printf("TEST2"); #define CHOOSER(x, y,FUNC,...) FUNC() #define MANIMACRO(...) CHOOSER(,__VA_ARGS__,TEST1,TEST2) int main(void) { MANIMACRO(1); MANIMACRO(); } The idea

问题 I was experimenting with C++11 variadac macros. I was trying to apply another macro to each argument in the list. This is my first try: #define APPLY_CHAIN(first, ...) APPLY_ACT(first) APPLY_CHAIN( __VA_ARGS__ ) Unfortunately this did not work. I eventually got it to work. But it was a bit convoluted and has a limit of 'n' (where 'n' is a max size that I am willing to type macros for). #define COUNT_N(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, N, ...) N #define COUNT(...) COUNT_N( __VA_ARGS__,