具有零参数的可变参数宏 [英] Variadic macros with zero arguments

问题描述

我正在处理呼叫宏，

#define CALL(f,...) FN(f)->call((ref(new LinkedList()), __VA_ARGS__))

被调用时

CALL(print,2,3,4,5);

将2 3 4 5添加到链接列表(这样做很重载)并调用print，它期望链接列表能够按预期工作，而无论是否有一些不需要参数的调用，

adds 2 3 4 5 to the linked list (, is overloaded to do so) and calls print which expects a linked list which works as expected how ever there are some calls which do not require arguments,

CALL(HeapSize);

它仍然需要一个链表，但是一个空的表，上面的行不通，我想提出一个可以使用任何一种样式的宏?

It still takes a linked list but an empty one, above does not work, I am trying to come up with a macro that woud work with either style?

在gcc文档中进行挖掘，我发现在 VA_ARGS 之前添加##会删除，当没有参数但无法嵌套宏时，

Digging throug gcc docs I found that adding ## before VA_ARGS removes the , when there are no arguments but with that I can not nest macros,

CALL(print,CALL(HeadSize));

这会导致CALL未定义错误，如果我分开它可以正常工作的呼叫

this causes CALL not defined error how ever if I separate the the calls it works

推荐答案

对于更新后的问题，通过使用辅助宏VA_ARGS 接下来，参数将按预期扩展.

As for the updated question, by the use of auxiliary macro VA_ARGS like the following, the arguments will be expanded as expected.

#define VA_ARGS(...) , ##__VA_ARGS__
#define CALL(f,...) FN(f)->call((ref(new LinkedList()) VA_ARGS(__VA_ARGS__)))

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