在C中使用不带括号的参数调用函数?

问题描述

当一个函数没有任何参数时，可以通过 define as

When a function does not have any argument, it is possible to call it without parenthesis by define as

#define test test()

是否可以在不带括号的情况下调用带有参数的函数?像

Is it possible to call a function with argument without paranthesis? Something like

#define test test(char *arg)

test "argument 1";

推荐答案

在C语言中，这是不可能的.标准(C99)的6.5.2节描述了后缀表达式，并且没有类似的语法.函数调用为(§6.5.2.2):

That's not going to be possible in C the way you have it. §6.5.2 of the standard (C99) describes postfix expressions, and has no syntax like that. Function calls are (§6.5.2.2):

括号不是可选的，它们需要包装所有参数，因此您需要一个类似函数的宏(在调用"站点需要括号)或两个单独的东西(一个用于插入起始括号，一个用于插入).插入结束符).

Parens are not optional, and they need to wrap all the arguments so you need either a function-like macro (which requires parens at the "call" site) or two separate things (one to insert the starting paren, one to insert the closing one).

您可以这样做:

#define test puts(
#define end  );
#define int_proc int
#define proc_body {
#define proc_end  }
#define no_args (void)
#include <stdio.h>

int_proc main no_args
proc_body
  test "hello" end
proc_end

但是...真的吗?

C ++特别提供了运算符重载的更多可能性.如果您要自定义"某些语法，则可能需要调查一下.

C++ offers more possibilities with operator overloading in particular. You might want to look into that if you want to "customize" some syntax.

这是一个可怕的例子:

#include <iostream>

struct Foo {
    void operator=(char const* str)
    {
        std::cout << str << std::endl;
    }
};
Foo global_foo;

#define test global_foo =

int main()
{
    test "hello";
}

请注意，您可能会发现一些明智的方法，例如Qt的 qDebug 实用工具类.从示意图上看，它是这样的:

Note that there are sane approaches that you might find attractive, e.g. Qt's qDebug utility class. Schematically, it goes like this:

#include <iostream>

struct debug {
    debug() {}
    ~debug()
    {
        std::cout << std::endl;
    }
    debug const& operator<<(char const* msg) const
    {
        std::cout << msg << " ";
        return *this;
    }
};

通常的使用方式是:

debug() << "this" << "works";

如果您添加采用 char const * 的构造函数:

If you add a constructor that takes char const*:

debug(char const*msg)
{
    std::cout << msg << " ";
}

然后，您可以使用强制转换符号并编写:

Then you can use cast notation and write:

(debug) "Hello";

与您所拥有的(和可宏化的)非常接近.

Which is pretty close to what you had (and is macroable).

然后，您可以与所有其他运算符( operator，将是主要的候选对象)结合在一起，但是优先规则可能会破坏这种乐趣.

Then you can get fancy with all the other operators (operator, would be a prime candidate), but precedence rules might ruin the fun a bit.

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