结构内使用typedef命名和索引文本命令 [英] Use typedef within struct for naming and indexing text commands

问题描述

我用一个简单的命令行应用程序，它发生在ASCI文字和跨$ P $点作为一个命令工作。

I am working with a simple command line application that takes in ASCI text and interprets it as a command.

我试图在 HTTP尽量减少通过例如该应用程序的冗余：// gcc.gnu.org/onlinedocs/cpp/Concatenation.html 。

例如：
考虑到除$ P $点命名命令的C程序。有可能需要的命令的表，可能宣布结构的阵列，如下所示：

eg: Consider a C program that interprets named commands. There probably needs to be a table of commands, perhaps an array of structures declared as follows:

 struct command
 {
   char *name;
   void (*function) (void);
 };

 struct command commands[] =
 {
   { "quit", quit_command },
   { "help", help_command },
   ...
 };

这将是清洁不必须给每个命令的名字两次，一次在字符串常量，一次函数名。作为一个参数，它接受一个命令的名字一个宏可以使这种不必要的。字符串常量可以用字串化，并通过连接用`_command参数中的函数名称创建。下面是它是如何做的：

It would be cleaner not to have to give each command name twice, once in the string constant and once in the function name. A macro which takes the name of a command as an argument can make this unnecessary. The string constant can be created with stringification, and the function name by concatenating the argument with `_command'. Here is how it is done:

 #define COMMAND(NAME)  { #NAME, NAME ## _command }

 struct command commands[] =
 {
   COMMAND (quit),
   COMMAND (help),
   ...
 };

现在，让我们说，我希望有一个命令字符串和索引（即：INT）值，而不是一个字符串函数指针

Now, let's say that I want to have a command string and index (ie: int) value, rather than a string and function pointer.

 struct command
 {
   char *name;
   int command_idx;
 };

现在，我已经命名的命令，并具有某种指标我可以使用稍后以编程方式确定每个命令的手段。例如，我有一个在命令指数运行的switch语句。如果我想对这些指标的工作，我必须先手动设置的值。

Now, I have a means to name commands, and have some sort of index I can use later on to identify each command programatically. For example, I have a switch statement that operates on the command index. If I want to work on these indexes, I have to manually set the values first.

我可以手动创建一个枚举数据类型，但我有一个单独的枚举声明定义枚举常量。 IE浏览器：
枚举命令{cmd_quit = 0，cmd_help}
而在最后，我还是最终不得不键入每个命令名称两次：在我的枚举通过命令（）宏一次，然后再次

I can manually create an enumerated data type, but then I have define the enumerated constants in a separate enum statement. IE: enum commands { cmd_quit = 0, cmd_help } and in the end, I still end up having to type each command name twice: once via the COMMAND() macro, and again in my enum.

有没有使用C preprocessor，让我来创建一个宏创建命令结构（用绳子和int成员）自动编号​​的int值（command_idx）为我增加更多的方法，以及通过命令（）宏命令？

Is there any method using the C preprocessor that would allow me to create a macro creates the "command" struct (with string and int members), and auto-numbers the int value (command_idx) as I add more commands via the COMMAND() macro?

我也知道，我可以只使用STRCMP（）调用每个可能的命令，并比较由用户提供的输入，但我想通过command_idx值有索引的直接手段进入命令，不是每次strcmp'ing对命令的大规模列表（即：O型，而不是O（1）（N））。我也想避免必须不惜一切代价超过一次键入命令的名称。

I am also aware that I can just use strcmp() calls on each possible command, and compare to the input provided by the user, but I would like to have a direct means of indexing into commands via the command_idx value, as opposed to strcmp'ing against a massive list of commands each time (ie: O(1) instead of O(n) ). I also want to avoid having to type the command name more than once at all costs.

谢谢！

推荐答案

您可以使用宏重新定义实现这一目标。首先，创建一个文件，该文件仅列出叫你的命令 commands.inc ：

You can use macro redefinition to achieve this. First, you create a file that simply lists your commands called commands.inc:

COMMAND(quit)
COMMAND(help)
...

然后，在你的C源代码，你可以的#includecommands.inc多次，（）命令的不同定义有效控制它是如何工作的。例如：

Then, in your C source you can #include "commands.inc" multiple times, with different definitions of COMMAND() in effect to control how it works. For example:

struct command
{
   char *name;
   int command_idx;
};

#define COMMAND(NAME) CMD_ ## NAME,

enum command_enum {
#include "commands.inc"
};

#undef COMMAND

#define COMMAND(NAME) { #NAME, CMD_ ## NAME },

struct command commands[] =
{
#include "commands.inc"
};

#undef COMMAND

（注意，这个特殊的例子依赖于C99的改进，它允许一个尾随，在该枚举的声明和复合初始化器 - 你可以很容易解决，在C89通过添加在最后一个虚拟的条目）

(Note that this particular example relies on a C99 improvement that allows a trailing , at the end of the lists in the enum declaration and compound initialiser - you can easily work around that in C89 by adding a dummy entry at the end).

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