objective-c - 编译器无法识别 switch 语句中的 typedef

Question

我刚刚开始学习objective c，我在玩typedef、枚举、switch语句和函数，只是为了更熟悉它们。根据我的理解，这段代码应该都可以工作，但是我在声明 switch 语句的位置出现编译错误，上面写着“意外的类型名称'dinnerPreference'：预期的表达式。如果我使用 typedef 来定义dinnerPreference，那么为什么会发生这种情况。

typedef  enum { pizza = 0, steak = 1, seafood = 2} dinnerPreference;
int main(int argc, const char * argv[])
{

@autoreleasepool {


    dinnerPreference momDinnPref = pizza;
    dinnerPreference myDinnPref  = steak;
    dinnerPreference urDinnPref  = seafood;

    int dinnerPrefFunc ( dinnerPreference x ); {
        NSLog(@"Lets see what this guy wants for dinner");
        dinnerPreference x
        switch( dinnerPreference x ) {
            case pizza:
                NSLog(@"This person wants pizza");
                break;
            case steak:
                NSLog(@"This person wants steak");
                break;
            case seafood:
                NSLog(@"This person wants steak");
                break;
            default:
                NSLog(@"I dunno");
                break;
                return 0;
        };
    }
    dinnerPrefFunc(momDinnPref);
    dinnerPrefFunc(myDinnPref);
    dinnerPrefFunc(urDinnPref);
}
return 0;

Answer 1

Objective-C（和 C、C++）不支持在其他函数中声明函数，至少不支持您尝试过的方式。尝试重新排序您的代码，如下所示：

typedef enum { pizza = 0, steak = 1, seafood = 2 } dinnerPreference;

int dinnerPrefFunc ( dinnerPreference x );
int dinnerPrefFunc ( dinnerPreference x )
{
    NSLog(@"Lets see what this guy wants for dinner");
    switch( x )
    {
        case pizza:
            NSLog(@"This person wants pizza");
            break;
        case steak:
            NSLog(@"This person wants steak");
            break;
        case seafood:
            NSLog(@"This person wants steak");
            break;
        default:
            NSLog(@"I dunno");
            break;
    }
    return 0;
}

int main(int argc, const char * argv[])
{

   @autoreleasepool
   {

      dinnerPreference momDinnPref = pizza;
      dinnerPreference myDinnPref  = steak;
      dinnerPreference urDinnPref  = seafood;

      dinnerPrefFunc(momDinnPref);
      dinnerPrefFunc(myDinnPref);
      dinnerPrefFunc(urDinnPref);
   }
   return 0;
}

Answer 2

这一行是错误的：

switch( dinnerPreference x ) {

将其更改为：

switch (x) {

还要注意，你还没有初始化 x。