在struct中使用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

我正在使用一个简单的命令行应用程序，它接受ASCI文本并将其解释为命令。

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

我试图通过 http://gcc.gnu.org/onlinedocs/cpp/Concatenation.html 。

例如：
考虑一个解释命名命令的C程序。可能需要一个命令表，可能是一个声明如下的结构数组：

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 },
   ...
 };

这将更清洁，不必给每个命令两次，一次在字符串常量和一次在函数名中。将命令的名称作为参数的宏可以使这不必要。可以使用字符串化创建字符串常量，并通过将参数与`_command'连接来创建函数名称。下面是如何完成的：

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，假设我想要一个命令字符串和索引而非字符串和函数指针。

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，我有一种命名命令的方法，以编程方式识别每个命令。例如，我有一个switch语句，对命令索引进行操作。如果我想处理这些索引，我必须手动设置值。

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，但是我已经在一个单独的枚举语句中定义了枚举常量。 IE：
枚举命令{cmd_quit = 0，cmd_help}
，最后，我仍然需要输入两个命令名两次：一次通过COMMAND（）宏，再次在我的枚举。

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.

有没有任何方法使用C预处理器，允许我创建一个宏创建命令结构（带有字符串和int成员），并自动编号int value（command_idx）我通过COMMAND（）宏添加更多的命令？

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并与用户提供的输入进行比较，但我想有一个直接的方法通过command_idx值索引到命令，而不是strcmp'ing大量的命令每次（即：O（1）而不是的O（n））。我也想避免不得不多次输入命令名。

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

您可以使用宏重定义来实现这一点。首先，创建一个简单列出您的命令 commands.inc 的文件：

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，在您的C源中，您可以多次使用 COMMAND（） #includecommands.inc c>有效地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

（请注意，此特定示例依赖于C99改进，允许在枚举声明和复合初始化程序中的列表末尾的结尾，在C89中，通过在结尾添加一个虚拟条目）。

(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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