c-preprocessor

问题 I have a hypothetical UIViewController class named "foo". foo inherits from class bar and class bar #import's "Class A", a class which foo uses extensively. The problem is, when I'm using an instance of class A in foo, I don't get any compiler errors, but I do get a warning for instance, that an instance of Class A does not respond to a particular method. Do I have to explicitly #import ClassA.h into class 'foo'? even though class foo extends extends bar, which already imports it? Hope that's

问题 I have a number of very long arrays. No run-time sort is possible. It is also time consuming to sort them manually. Moreover, new elements can be added in any order later, so I would like to sort them by value using C preprocessor or maybe there is any compilers flag (GCC)? For example: sometype S[] = { {somevals, "BOB", someothervals}, {somevals, "ALICE", someothervals}, {somevals, "TIM", someothervals}, } must be sorted so: sometype S[] = { {somevals, "ALICE", someothervals}, {somevals,

问题 Given the C file below: $ cat macros.c #ifdef MACRO # error MACRO is defined #else # error MACRO is undefined #endif #if MACRO # error MACRO is non-zero #else # error MACRO is zero #endif What is the expected output of the following? $ gcc -c macros.c $ gcc -DMACRO -c macros.c $ gcc -DMACRO=0 -c macros.c Answer : Here's what the gcc's preprocessor on my machine does. $ gcc -c macros.c macros.c:4:4: error: #error MACRO is undefined macros.c:9:4: error: #error MACRO is zero $ gcc -DMACRO -c

问题 I have this code which works: #include <stdio.h> #define A(x) x B #define B(x) C(x, #define C(x,y) y x) int main( void ) { printf( A("1") ("2") "3" ); } It prints 132 (the point of the A macro is to swap the thing which follows its parameters in brackets with everything after that until another closing bracket) But if I use that within another macro: #define Z(x) x printf( Z( A("1") ("2") "3" ) ); I get the compile error "Unterminated function-like macro invocation". I realise that this

问题 After reading about VA_NARG I tried to implement function overloading depending on number of arguments in C using macros. Now the problem is: void hello1(char *s) { ... } void hello2(char *s, char *t) { ... } // PP_NARG(...) macro returns number of arguments :ref to link above // does not work #define hello(...) hello ## PP_NARG(__VA_ARGS__) int main(void) { hello("hi"); // call hello1("hi"); hello("foo","bar"); // call hello2("foo","bar"); return 0; } I've read this from C-faq. But still

问题 This is really odd: : josh@josh; wget ftp://ftp.ruby-lang.org/pub/ruby/1.8/ruby-1.8.7.tar.bz2 : josh@josh; tar xvjf ruby-1.8.7.tar.bz2 : josh@josh; cd ruby-1.8.7/ : josh@josh; CFLAGS='-O0 -g -Wall' ./configure --disable-pthread : josh@josh; make gcc -O0 -g -Wall -DRUBY_EXPORT -D_GNU_SOURCE=1 -I. -I. -c array.c [...] gcc -O0 -g -Wall -DRUBY_EXPORT -D_GNU_SOURCE=1 -I. -I. -c math.c math.c: In function ‘domain_check’: math.c:37: error: missing binary operator before token "(" make: *** [math.o]

问题 Is it legal to invoke a variadic macro M with no arguments for its variadic parameter? The relevant standard quote is [cpp.replace]/4 : If the identifier-list in the macro definition does not end with an ellipsis, the number of arguments (including those arguments consisting of no preprocessing tokens) in an invocation of a function-like macro shall equal the number of parameters in the macro definition. Otherwise, there shall be more arguments in the invocation than there are parameters in

问题 This question already has answers here : msbuild, defining Conditional Compilation Symbols (4 answers) Closed 2 years ago . I need to create a demo version of an existing large application consisting of multiple projects. I'd like to use the existing projects, and just neuter the functionality via preprocessor directives #if DEMO mycode.NeuterNow(); #endif We are building our app using MSBuild, and I'd ideally use something along the lines of: MSBuild -DefineProperty:DEMO MySolution.sln Does

问题 I want to generate many sub-class which only has little difference, so I want to use macro to simplify my job. The macro define below: #define DECLARE_SUB_CLASS(sub_class_name, base_class_name, value1) \ class sub_class_name:base_class_name \ { \ public: \ virtual int initialize(const void *); \ virtual int run(const void *); \ virtual void reset(); \ virtual int output(const char*); \ virtual void terminate(); \ private: \ static const char m_szValue=#value1; \ }; I use it like this: DECLARE

问题 This question already has an answer here : Macro in Objective-C calling isEqualToString: produces error about invalid token (1 answer) Closed 3 years ago . #define A7VERSION() ({[[[[[UIDevice currentDevice] systemVersion] componentsSeparatedByString:@"."] objectAtIndex:0] intValue];}) #define IS_OS_7 A7VERSION()>=7 The above declaration seems to compile well. But as soon as I add it a .m file I get the following exception "invalid token at start of a preprocessor expression". I am not able to