| // Copyright 2019 The Pigweed Authors |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); you may not |
| // use this file except in compliance with the License. You may obtain a copy of |
| // the License at |
| // |
| // https://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT |
| // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the |
| // License for the specific language governing permissions and limitations under |
| // the License. |
| // |
| // Macros for counting the number of arguments passed to a variadic |
| // function-like macro. |
| #pragma once |
| |
| #include "pw_preprocessor/boolean.h" |
| |
| // PW_ARG_COUNT counts the number of arguments it was called with. It evalulates |
| // to an integer literal in the range 0 to 64. Counting more than 64 arguments |
| // is not currently supported. |
| // |
| // PW_ARG_COUNT is most commonly used to count __VA_ARGS__ in a variadic macro. |
| // For example, the following code counts the number of arguments passed to a |
| // logging macro: |
| // |
| /* #define LOG_INFO(format, ...) { \ |
| static const int kArgCount = PW_ARG_COUNT(__VA_ARGS__); \ |
| SendLog(kArgCount, format, ##__VA_ARGS__); \ |
| } |
| */ |
| // clang-format off |
| #define PW_ARG_COUNT(...) \ |
| _PW_ARG_COUNT_IMPL(__VA_ARGS__, \ |
| 64, 63, 62, 61, 60, 59, 58, 57, \ |
| 56, 55, 54, 53, 52, 51, 50, 49, \ |
| 48, 47, 46, 45, 44, 43, 42, 41, \ |
| 40, 39, 38, 37, 36, 35, 34, 33, \ |
| 32, 31, 30, 29, 28, 27, 26, 25, \ |
| 24, 23, 22, 21, 20, 19, 18, 17, \ |
| 16, 15, 14, 13, 12, 11, 10, 9, \ |
| 8, 7, 6, 5, 4, 3, 2, PW_HAS_ARGS(__VA_ARGS__)) |
| |
| // Expands to 1 if one or more arguments are provided, 0 otherwise. |
| #define PW_HAS_ARGS(...) PW_NOT(PW_HAS_NO_ARGS(__VA_ARGS__)) |
| |
| // Expands to 0 if one or more arguments are provided, 1 otherwise. This |
| // approach is from Jens Gustedt's blog: |
| // https://gustedt.wordpress.com/2010/06/08/detect-empty-macro-arguments/ |
| // |
| // Normally, with a standard-compliant C preprocessor, it's impossible to tell |
| // whether a variadic macro was called with no arguments or with one argument. |
| // A macro invoked with no arguments is actually passed one empty argument. |
| // |
| // This macro works by checking for the presense of a comma in four situations. |
| // These situations give the following information about __VA_ARGS__: |
| // |
| // 1. It is two or more variadic arguments. |
| // 2. It expands to one argument surrounded by parentheses. |
| // 3. It is a function-like macro that produces a comma when invoked. |
| // 4. It does not interfere with calling a macro when placed between it and |
| // parentheses. |
| // |
| // If a comma is not present in 1, 2, 3, but is present in 4, then __VA_ARGS__ |
| // is empty. For this case (0001), and only this case, a corresponding macro |
| // that expands to a comma is defined. The presence of this comma determines |
| // whether any arguments were passed in. |
| // |
| // C++20 introduces __VA_OPT__, which would greatly simplify this macro. |
| #define PW_HAS_NO_ARGS(...) \ |
| _PW_HAS_NO_ARGS(_PW_HAS_COMMA(__VA_ARGS__), \ |
| _PW_HAS_COMMA(_PW_MAKE_COMMA_IF_CALLED __VA_ARGS__), \ |
| _PW_HAS_COMMA(__VA_ARGS__()), \ |
| _PW_HAS_COMMA(_PW_MAKE_COMMA_IF_CALLED __VA_ARGS__())) |
| |
| #define _PW_HAS_COMMA(...) \ |
| _PW_ARG_COUNT_IMPL(__VA_ARGS__, \ |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \ |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \ |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \ |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0) |
| |
| #define _PW_ARG_COUNT_IMPL(a64, a63, a62, a61, a60, a59, a58, a57, \ |
| a56, a55, a54, a53, a52, a51, a50, a49, \ |
| a48, a47, a46, a45, a44, a43, a42, a41, \ |
| a40, a39, a38, a37, a36, a35, a34, a33, \ |
| a32, a31, a30, a29, a28, a27, a26, a25, \ |
| a24, a23, a22, a21, a20, a19, a18, a17, \ |
| a16, a15, a14, a13, a12, a11, a10, a09, \ |
| a08, a07, a06, a05, a04, a03, a02, a01, \ |
| count, ...) \ |
| count |
| |
| // clang-format on |
| #define _PW_HAS_NO_ARGS(a1, a2, a3, a4) \ |
| _PW_HAS_COMMA(_PW_PASTE_RESULTS(a1, a2, a3, a4)) |
| #define _PW_PASTE_RESULTS(a1, a2, a3, a4) _PW_HAS_COMMA_CASE_##a1##a2##a3##a4 |
| #define _PW_HAS_COMMA_CASE_0001 , |
| #define _PW_MAKE_COMMA_IF_CALLED(...) , |
| |
| // Expands to a comma followed by __VA_ARGS__, if __VA_ARGS__ is non-empty. |
| // Otherwise, expands to nothing. This is useful when calling a function with |
| // __VA_ARGS__, since it removes the extra comma when no arguments are |
| // provided. |
| // |
| // This is a more flexible, standard-compliant version of ##__VA_ARGS__. Unlike |
| // ##__VA_ARGS__, this can be used to eliminate an unwanted comma when |
| // __VA_ARGS__ expands to an empty argument because an outer macro was called |
| // with __VA_ARGS__ instead of ##__VA_ARGS__. |
| // |
| // This can be used to call variadic functions or provide variadic template |
| // parameters from a macro. For example: |
| // |
| // #define MY_PRINTF(fmt, ...) MY_PRINTF_IMPL(fmt, __VA_ARGS__) |
| // #define MY_PRINTF_IMPL(fmt, ...) printf(fmt PW_COMMA_ARGS(__VA_ARGS__)) |
| // |
| #define PW_COMMA_ARGS(...) _PW_COMMA_ARGS(PW_HAS_ARGS(__VA_ARGS__), __VA_ARGS__) |
| |
| #define _PW_COMMA_ARGS(has_args, ...) _PW_COMMA_ARGS_X(has_args, __VA_ARGS__) |
| #define _PW_COMMA_ARGS_X(has_args, ...) _PW_COMMA_ARGS_##has_args(__VA_ARGS__) |
| #define _PW_COMMA_ARGS_0(...) // no args, no comma |
| #define _PW_COMMA_ARGS_1(...) , __VA_ARGS__ // comma, followed by args |