宏中的语句内的逗号被误解为宏参数分隔符 [英] Comma inside a statement inside a macro being misinterpreted as a macro argument separator

问题描述

我刚刚创建了一个Xcode项目，并编写了以下代码:

I just created an Xcode project and wrote the following code:

#define foo(x) x
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    int n = 666;
    NSString* string = foo([NSString stringWithFormat: @"%d", n]);
    NSLog (@"string is %@", string);
    [self.window makeKeyAndVisible];
        return YES;
}

当我尝试运行此命令时，我遇到了很多错误，因为预处理程序确定stringWithFormat:之后的逗号应该分隔两个宏参数，因此我将foo与两个参数一起使用，而不是正确的参数

When I try to run this, I get a bunch of errors, because the preprocessor decides that that comma after the stringWithFormat: is supposed to be separating two macro arguments, therefore I have used foo with two arguments instead of the correct one.

因此，当我要在宏的语句中使用逗号时，该怎么办?

So when I want a comma inside a statement inside my macro, what can I do?

此C ++问题提出了一种放置圆角括号的方法()围绕逗号，这显然使预处理器意识到逗号不是宏参数分隔符.但是，从我的头顶上，我没有想到在目标C中做到这一点的方法.

This C++ question suggests a way to put some round parens () around the comma, which apparently leads the preprocessor to realize that the comma is not a macro argument separator. But off the top of my head, I'm not thinking of a way to do that in objective C.

推荐答案

在调用工作周围添加其他括号:

Adding additional parentheses around the call works:

NSString* string = foo(([NSString stringWithFormat:@"%d",n]));

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