0. vs 查看预编译后的代码
1. # 和 ##
#define P(A) { printf(" the square of %s is %d ", #A, A * A); } #define Q(B) { printf(" the square of "#B" is %d " , B * B); } #define Handle(_name) struct _name##Handle { unsigned int idx; }; Handle(Shader); Handle(VertexBuffer); Handle(IndexBuffer); int main() { P(16); Q(25); IndexBufferHandle ibh; ibh.idx = 0; return 0; }
上面代码会展开成：
struct ShaderHandle { unsigned int idx; };; struct VertexBufferHandle { unsigned int idx; };; struct IndexBufferHandle { unsigned int idx; };; int main() { { printf(" the square of %s is %d ", "16", 16 * 16); }; { printf(" the square of ""25"" is %d " , 25 * 25); }; IndexBufferHandle ibh; ibh.idx = 0; return 0; }
2. BX_VA_ARGS_COUNT(...) -> 替换成参数列表的参数个数
#if BX_COMPILER_MSVC // Workaround MSVS bug... # define BX_VA_ARGS_PASS(...) BX_VA_ARGS_PASS_1_ __VA_ARGS__ BX_VA_ARGS_PASS_2_ # define BX_VA_ARGS_PASS_1_ ( # define BX_VA_ARGS_PASS_2_ ) #else # define BX_VA_ARGS_PASS(...) (__VA_ARGS__) #endif // BX_COMPILER_MSVC #define BX_VA_ARGS_COUNT(...) BX_VA_ARGS_COUNT_ BX_VA_ARGS_PASS(__VA_ARGS__, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0) #define BX_VA_ARGS_COUNT_(_a1, _a2, _a3, _a4, _a5, _a6, _a7, _a8, _a9, _a10, _a11, _a12, _a13, _a14, _a15, _a16, _last, ...) _last int main() { auto v = BX_VA_ARGS_COUNT(42, 11); std::cout << v << std::endl; return 0; }
预编译后：
int main() {
auto v = 2;
std::cout << v << std::endl;
return 0；
}
3. BX_UNUSED(...)
#define BX_MACRO_BLOCK_BEGIN for(;;) { #define BX_MACRO_BLOCK_END break; } #define BX_NOOP(...) BX_MACRO_BLOCK_BEGIN BX_MACRO_BLOCK_END #define BX_PRAGMA_DIAGNOSTIC_PUSH BX_PRAGMA_DIAGNOSTIC_PUSH_MSVC_ #define BX_PRAGMA_DIAGNOSTIC_POP BX_PRAGMA_DIAGNOSTIC_POP_MSVC_ #define BX_PRAGMA_DIAGNOSTIC_IGNORED_CLANG_GCC(_x) #define BX_PRAGMA_DIAGNOSTIC_PUSH_MSVC_() __pragma(warning(push) ) #define BX_PRAGMA_DIAGNOSTIC_POP_MSVC_() __pragma(warning(pop) ) #define BX_PRAGMA_DIAGNOSTIC_IGNORED_MSVC(_x) __pragma(warning(disable:_x) ) #define BX_MACRO_DISPATCHER(_func, ...) BX_MACRO_DISPATCHER_1_(_func, BX_VA_ARGS_COUNT(__VA_ARGS__) ) #define BX_MACRO_DISPATCHER_1_(_func, _argCount) BX_MACRO_DISPATCHER_2_(_func, _argCount) #define BX_MACRO_DISPATCHER_2_(_func, _argCount) BX_CONCATENATE(_func, _argCount) #define BX_CONCATENATE(_x, _y) BX_CONCATENATE_(_x, _y) #define BX_CONCATENATE_(_x, _y) _x ## _y #if BX_COMPILER_MSVC // Workaround MSVS bug... # define BX_UNUSED(...) BX_MACRO_DISPATCHER(BX_UNUSED_, __VA_ARGS__) BX_VA_ARGS_PASS(__VA_ARGS__) #else # define BX_UNUSED(...) BX_MACRO_DISPATCHER(BX_UNUSED_, __VA_ARGS__)(__VA_ARGS__) #endif // BX_COMPILER_MSVC #define BX_UNUSED_1(_a1) BX_MACRO_BLOCK_BEGIN BX_PRAGMA_DIAGNOSTIC_PUSH(); /*BX_PRAGMA_DIAGNOSTIC_IGNORED_CLANG_GCC("-Wuseless-cast");*/ (void)(true ? (void)0 : ( (void)(_a1) ) ); BX_PRAGMA_DIAGNOSTIC_POP(); BX_MACRO_BLOCK_END #define BX_UNUSED_2(_a1, _a2) BX_UNUSED_1(_a1); BX_UNUSED_1(_a2) #define BX_UNUSED_3(_a1, _a2, _a3) BX_UNUSED_2(_a1, _a2); BX_UNUSED_1(_a3) #define BX_UNUSED_4(_a1, _a2, _a3, _a4) BX_UNUSED_3(_a1, _a2, _a3); BX_UNUSED_1(_a4) #define BX_UNUSED_5(_a1, _a2, _a3, _a4, _a5) BX_UNUSED_4(_a1, _a2, _a3, _a4); BX_UNUSED_1(_a5) #define BX_UNUSED_6(_a1, _a2, _a3, _a4, _a5, _a6) BX_UNUSED_5(_a1, _a2, _a3, _a4, _a5); BX_UNUSED_1(_a6) #define BX_UNUSED_7(_a1, _a2, _a3, _a4, _a5, _a6, _a7) BX_UNUSED_6(_a1, _a2, _a3, _a4, _a5, _a6); BX_UNUSED_1(_a7) #define BX_UNUSED_8(_a1, _a2, _a3, _a4, _a5, _a6, _a7, _a8) BX_UNUSED_7(_a1, _a2, _a3, _a4, _a5, _a6, _a7); BX_UNUSED_1(_a8) #define BX_UNUSED_9(_a1, _a2, _a3, _a4, _a5, _a6, _a7, _a8, _a9) BX_UNUSED_8(_a1, _a2, _a3, _a4, _a5, _a6, _a7, _a8); BX_UNUSED_1(_a9) #define BX_UNUSED_10(_a1, _a2, _a3, _a4, _a5, _a6, _a7, _a8, _a9, _a10) BX_UNUSED_9(_a1, _a2, _a3, _a4, _a5, _a6, _a7, _a8, _a9); BX_UNUSED_1(_a10) #define BX_UNUSED_11(_a1, _a2, _a3, _a4, _a5, _a6, _a7, _a8, _a9, _a10, _a11) BX_UNUSED_10(_a1, _a2, _a3, _a4, _a5, _a6, _a7, _a8, _a9, _a10); BX_UNUSED_1(_a11) #define BX_UNUSED_12(_a1, _a2, _a3, _a4, _a5, _a6, _a7, _a8, _a9, _a10, _a11, _a12) BX_UNUSED_11(_a1, _a2, _a3, _a4, _a5, _a6, _a7, _a8, _a9, _a10, _a11); BX_UNUSED_1(_a12) int main() { BX_UNUSED(42); return 0; }
展开成：
int main() {
for(;;) { __pragma(warning(push) ); (void)(true ? (void)0 : ( (void)(42) ) ); __pragma(warning(pop) ); break; };
return 0;
}
其中 #pragma warning( push / pop )的作用是：暂存或者恢复编译器的警告状态，比如：
#pragma warning( push ) #pragma warning( disable : 4705 ) #pragma warning( disable : 4706 ) #pragma warning( disable : 4707 ) // Some code #pragma warning( pop )
// Some code这块代码不会报4705-4707这几个错误