结构及在C标签联合

问题描述

#define HOST_NAME "UDP"
#define ADDRESS "127.0.0.1"
struct UDP_IP_Parameters {
        uint version; /* e.g. "1.0" = 0x0100 */
        uint port; /* PORT */
        taggedunion {
            "HOST_NAME" char[256];
            "ADDRESS" char[15];
        };
};

int main()
{
struct UDP_IP_Parameters udp;
udp.version = 0x0100;
udp.port = 444;

}

我已经创建了嵌套的结构和taggedunion。是否有可能定义主机名和地址恒定像上面？是否有可能通过为它创建一个对象分配一些值。任何人都可以给我一些想法。

I have created a structure and taggedunion nested within that. Is it possible to define the host name and address as constant like above ?? Is it possible to assign some values by creating a objects for it. Could anyone give me some ideas.

推荐答案

这不是C

没有，你可以不是一个类型声明中指定的值。

No, you can't specify values inside a type declaration.

你能做的最接近的是大概是这样的：

The closest you can do is probably something like:

typedef struct {
  uint16_t version; /* Guessing size requirements. */
  uint16_t port;
  bool resolved;
  union {
    char host_name[256];
    char address[24];
  } addr;
} UDP_IP_Parameters;

以上使用解析标志标签结合，以便程序可以知道哪个工会的成员是有效的。

The above uses the resolved flag to "tag" the union, so the program can know which member of the union is valid.

您应该能够初始化实例，像这样：

You should be able to initialize an instance like so:

UDP_IP_Parameters so = { 0x100, 80, false, { "stackoverflow.com" } };

不知道如果（在C99），你可以使用点语法来做到这一点：

Not sure if (in C99) you can use the dotted syntax to do this:

UDP_IP_Parameters so = { 0x100, 80, true, { .address = "198.252.206.16" } };

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