c++ - 结构的存储大小未知 C++

Question

执行此操作时出现以下错误

“错误:‘mscp_commands’的存储大小未知”

struct command mscp_commands[]; /* forward declaration */

稍后我有:

struct command mscp_commands[] = {
 { "help",      cmd_help,       "show this list of commands"            },
 { "bd",        cmd_bd,         "display board"                         },
 { "ls",        cmd_list_moves, "list moves"                            },
 { "new",       cmd_new,        "new game"                              },
 { "go",        cmd_go,         "computer starts playing"               },
 { "test",      cmd_test,       "search (depth)"                        },
 { "quit",      cmd_quit,       "leave chess program"                   },
 { "sd",        cmd_set_depth,  "set maximum search depth (plies)"      },
 { "both",      cmd_both,       "computer plays both sides"             },
};

以这种方式向前声明 struct mscp_commands 有什么问题？

command struct 定义较早:

struct command {
    char *name;
    void (*cmd)(char*);
    char *help;
};

Answer 1

struct command mscp_commands[]; 是定义而不是声明(假设定义了 struct command)，但它不知道此时的存储大小，因为 mscp_commands 中的元素数量未知。这是 [] 与 * 明显不同的情况之一。

但是你可以这样写:

extern struct command mscp_commands[];

这确实是一个声明。