有很多关于如何定义相互引用的结构的帖子，但是我没有看到关于用这些定义的结构创建的变量的帖子。
我有许多菜单可以在我的产品中导航，由两个结构表示。此代码构建了我想要的结构：
<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0" xmlns:landxml="http://www.landxml.org/schema/LandXML-1.2" xmlns:hexagon="http://xml.hexagon.com/schema/HeXML-1.7" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text" version="1.0" encoding="UTF-16" indent="no" omit-xml-declaration="yes"/>
<xsl:variable name="XML" select="/"/>
<xsl:variable name="fileExt" select="'txt'"/>
<xsl:variable name="fileDesc" select="'Output pointno, easting, northing, and ortho height to three decimal places. + handling of linecodes e.g. (40,41)'"/>
<xsl:template match="/">
<xsl:for-each select="$XML">
<xsl:for-each select="landxml:LandXML">
<xsl:for-each select="hexagon:HexagonLandXML">
<xsl:for-each select="hexagon:Point">
<xsl:for-each select="@uniqueID">
<xsl:value-of select="string(.)"/>
<xsl:text>,</xsl:text>
</xsl:for-each>
<xsl:for-each select="hexagon:Coordinates">
<xsl:for-each select="hexagon:Local">
<xsl:for-each select="hexagon:Grid">
<xsl:for-each select="@e">
<xsl:value-of select='format-number(., "########.000")' />
<xsl:text>,</xsl:text>
</xsl:for-each>
<xsl:for-each select="@n">
<xsl:value-of select='format-number(., "########.000")' />
<xsl:text>,</xsl:text>
</xsl:for-each>
<xsl:for-each select="@hghthO">
<xsl:value-of select='format-number(., "########.000")' />
<xsl:text>,</xsl:text>
</xsl:for-each>
</xsl:for-each>
</xsl:for-each>
</xsl:for-each>
<xsl:for-each select="hexagon:PointCode">
<xsl:value-of select="string(@code)"/>
<xsl:text>,</xsl:text>
<xsl:if test="@codeLinework='open line'" >
<xsl:choose>
<xsl:when test="../@lineworkFlag='START LINJE'">
<xsl:text>40</xsl:text>
<xsl:text>,</xsl:text>
</xsl:when>
<xsl:when test="../following-sibling::*[1]/PointCode[@codeLinework='none']">
<xsl:text>41</xsl:text>
<xsl:text>,</xsl:text>
</xsl:when>
<!-- <xsl:when test="../@codeLinework">
<xsl:text> </xsl:text>
<xsl:text>,</xsl:text>
</xsl:when>-->
</xsl:choose>
</xsl:if>
<xsl:if test="@codeLinework='none'">
<xsl:text>30</xsl:text>
<xsl:text>,</xsl:text>
</xsl:if>
</xsl:for-each>
<xsl:text>
</xsl:text>
</xsl:for-each>
</xsl:for-each>
</xsl:for-each>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>
让我对此代码感到困惑的是“extern”关键字。我需要它来编译，但由于结构是在同一个文件中定义的，因此感觉应该有更好的方法来编写代码。我绝对不希望将所有声明都放在头文件中，因为使用终端的代码都不应该直接访问这些结构。通常我会克服错误并继续编码，但这个来源实际上会被客户看到。
有没有办法可以在没有“extern”关键字的情况下编写此代码？
答案 0 :(得分：1)
在标准C中，结构不等同于typedef
这个修改过的代码在标准的C编译器上编译：
typedef void (*MENU_FUNCTION_TYPE)();
typedef enum
{
MENU_INPUT_NAV, // Menu just navigates to other menus.
MENU_INPUT_ACTION, // Menu displays the results of an action.
MENU_INPUT_NUM, // Menu take numeric input and processes it.
NUM_MENU_INPUTS
} MENU_INPUT_TYPE;
// A menu is comprised of a list of menu items which you select with the number keys.
// This structure defines a menu and the menu items it contains.
typedef struct tag_MENU_ITEM_TYPE MENU_ITEM_TYPE;
typedef struct tag_MENU_TYPE
{
PGM_P text; // Pointer to text to display as menu name.
const MENU_ITEM_TYPE* menu_items; // Pointer to structures describing each menu item in this menu.
uint8_t num_items; // The number of menu item in this menu.
MENU_INPUT_TYPE type; // Specifies how this menu processes keyboard input.
} MENU_TYPE;
// This structure defines a menu item and what it does when you select it.
typedef struct tag_MENU_ITEM_TYPE
{
PGM_P text; // Pointer to text to display as menu item name.
const MENU_TYPE* link; // Pointer to which menu selecting this menu item takes you.
MENU_FUNCTION_TYPE action; // Pointer to function that is executed when this menu item is selected.
} MENU_ITEM_TYPE;
//These now acts as forward declarations
const MENU_TYPE PROGMEM main_menu;
const MENU_TYPE PROGMEM todo_menu;
const MENU_TYPE PROGMEM todo2_menu;
const MENU_TYPE PROGMEM todo3_menu;
const MENU_TYPE PROGMEM todo4_menu;
// **************************
// "Main Menu"
const char PROGMEM main_menu_text[] = "Main Menu";
const char PROGMEM main_menu_item_text1[] = "First Menu";
const char PROGMEM main_menu_item_text2[] = "Second Menu";
const char PROGMEM main_menu_item_text3[] = "Third Menu";
const char PROGMEM main_menu_item_text4[] = "Fourth Menu";
const MENU_ITEM_TYPE PROGMEM main_menu_items[] =
{
{main_menu_item_text1, &todo_menu, NULL},
{main_menu_item_text2, &todo2_menu, NULL},
{main_menu_item_text3, &todo3_menu, NULL},
{main_menu_item_text4, &todo4_menu, NULL}
};
const MENU_TYPE PROGMEM main_menu =
{
main_menu_text,
main_menu_items,
LENGTH(main_menu_items, MENU_ITEM_TYPE PROGMEM),
MENU_INPUT_NAV
};
// **************************
// "TODO Menu"
const char PROGMEM todo_menu_text[] = "TODO Menu";
const char PROGMEM todo_menu_item_text1[] = "todo";
const MENU_ITEM_TYPE PROGMEM todo_menu_items[] =
{
{todo_menu_item_text1, &todo2_menu, NULL}
};
const MENU_TYPE PROGMEM todo_menu =
{
todo_menu_text,
todo_menu_items,
LENGTH(todo_menu_items, MENU_ITEM_TYPE PROGMEM),
MENU_INPUT_NAV
};
// **************************
// "TODO2 Menu"
const char PROGMEM todo2_menu_text[] = "TODO2 Menu";
const char PROGMEM todo2_menu_item_text1[] = "todo2";
const MENU_ITEM_TYPE PROGMEM todo2_menu_items[] =
{
{todo2_menu_item_text1, &todo3_menu, NULL}
};
const MENU_TYPE PROGMEM todo2_menu =
{
todo2_menu_text,
todo2_menu_items,
LENGTH(todo2_menu_items, MENU_ITEM_TYPE PROGMEM),
MENU_INPUT_NAV
};
// **************************
// "TODO3 Menu"
const char PROGMEM todo3_menu_text[] = "TODO3 Menu";
const char PROGMEM todo3_menu_item_text1[] = "todo3";
const MENU_ITEM_TYPE PROGMEM todo3_menu_items[] =
{
{todo3_menu_item_text1, &todo4_menu, NULL}
};
const MENU_TYPE PROGMEM todo3_menu =
{
todo3_menu_text,
todo3_menu_items,
LENGTH(todo3_menu_items, MENU_ITEM_TYPE PROGMEM),
MENU_INPUT_NAV
};
// **************************
// "TODO4 Menu"
const char PROGMEM todo4_menu_text[] = "TODO4 Menu";
const MENU_TYPE PROGMEM todo4_menu =
{
todo4_menu_text,
NULL,
0,
MENU_INPUT_NUM
};
答案 1 :(得分：0)
如果这是用户可见的代码，并且您希望使用avr-gcc -std=c99 -Wall -Wextra和avr-g++ -std=c++11 -Wall -Wextra（加上-O和-mmcu=等选项进行编译而不会出现错误或警告你需要），我建议你隐藏宏中的脆弱部分，并使宏健壮。例如，使用与原始问题中显示的结构非常匹配的结构：
#include <avr/pgmspace.h>
#define JOIN2TOKENS(token1, token2) JOIN2TOKENS_(token1, token2)
#define JOIN2TOKENS_(token1, token2) token1 ## token2
struct menu_st {
const char *const title;
unsigned char const items;
const struct menuitem_st *const *const item;
};
struct menuitem_st {
const char *const label;
void (*const action)();
const struct menu_st *const submenu;
};
#define DECLARE_MENU(name, titlestr) \
extern const struct menu_st name PROGMEM; \
static const PROGMEM char JOIN2TOKENS(title_of__, name) [] PROGMEM = titlestr
#define DECLARE_MENUITEM(name, labelstr, funcptr, menuptr) \
static const char JOIN2TOKENS(label_of__, name) [] PROGMEM = labelstr; \
static const struct menuitem_st name [1] PROGMEM = { { JOIN2TOKENS(label_of__, name), funcptr, menuptr } }
#define DECLARE_SUBMENU(name, labelstr, tomenu) \
DECLARE_MENUITEM(name, labelstr, (void (*)())0, &(tomenu))
#define DECLARE_ACTION(name, labelstr, funcname) \
DECLARE_MENUITEM(name, labelstr, funcname, (const struct menu_st *const )0)
#define DECLARE_ACTSUB(name, labelstr, funcname, tomenu) \
DECLARE_MENUITEM(name, labelstr, funcname, &(tomenu))
#define DEFINE_MENU(name, ...) \
static const struct menuitem_st *const JOIN2TOKENS(menu_items_of__, name) [] PROGMEM = { __VA_ARGS__ }; \
const struct menu_st name PROGMEM = { \
JOIN2TOKENS(title_of__, name), \
sizeof (JOIN2TOKENS(menu_items_of__, name)) / sizeof (JOIN2TOKENS(menu_items_of__, name)[0]), \
JOIN2TOKENS(menu_items_of__, name), \
}
/* 0. Declare or define menu action functions.
* These are declared as static, so that they are only visible
* in the current compilation unit.
*
* As an example, action_1() and action_2() are defined here,
* but defaults() is only declared.
*/
static void action_1(void) { return; }
static void action_2(void) { return; }
static void defaults(void);
/* 1. Declare each menu.
*
* DECLARE_MENU(name, string)
* 'name' is the menu variable name, and
* 'string' is the menu title, a string literal.
*/
DECLARE_MENU(main_menu, "Main menu");
DECLARE_MENU(submenu_1, "First submenu");
DECLARE_MENU(submenu_2, "Second submenu");
/* 2. Declare each menu item. Below,
* 'name' is the local variable name (used in DEFINE_MENU()),
* 'string' is the text for this menu item,
* 'function' is the function called when the menu item is activated, and
* 'menu' is the name of the menu the menu item takes to.
*
* DECLARE_SUBMENU(name, string, menu)
* Declare a menu item, that takes to another menu.
*
* DECLARE_ACTION(name, string, function)
* Declare a menu item, that causes a function to be called.
*
* DECLARE_ABTSUB(name, string, function, menu)
* Declare a menu item, that causes a function to be called,
* and then changes to another menu.
*
*/
DECLARE_SUBMENU(to_main_menu, "Back to main menu", main_menu);
DECLARE_SUBMENU(to_submenu_1, "To first submenu", submenu_1);
DECLARE_SUBMENU(to_submenu_2, "To second submenu", submenu_2);
DECLARE_ACTION(do_action_1, "Action 1", action_1);
DECLARE_ACTION(do_action_2, "Action 2", action_2);
DECLARE_ACTSUB(do_defaults, "Reset to defaults", defaults, main_menu);
/* 3. Define which menus have which menu items.
*
* DEFINE_MENU(name, menu_item_1 [, ..., menu_item_N ])
* 'name' is the menu variable name, and should have been
* declared using DECLARE_MENU(name, string) before.
* 'menu_item_1' (and all additional parameters) are
* menu items declared before using
* DECLARE_SUBMENU(), DECLARE_ACTION(), or DECLARE_ACTSUB().
*/
DEFINE_MENU(main_menu, to_submenu_1, to_submenu_2);
DEFINE_MENU(submenu_1, to_submenu_2, do_action_1, do_action_2, to_main_menu);
DEFINE_MENU(submenu_2, to_submenu_1, do_defaults, to_main_menu);
/* 4. If the menu action functions were only declared earlier,
* define them here.
*/
static void defaults(void) { return; }
DECLARE_MENU()宏确实使用extern const来转发声明菜单结构。只有上面的菜单名称 - main_menu，submenu_1和submenu_2 - 在外部可见。这恰好在C99和C ++ 11中都能正常工作。如果您希望这些符号是本地符号，那么您需要为C99和C ++ 11提供不同的代码（可以通过#ifdef __cplusplus - #else - #endif来实现，但很难看，如果你问我）。
avr-gcc-4.8.2 -std=c99 -Wall -Wextra和avr-g++-4.8.2 -std=c++11 -Wall -Wextra都存储了.progmem.data部分中的所有数据结构。
请注意，由于GCC不支持多个地址空间（我最后检查的是avr-gcc-4.8.2），因此您必须使用pgm_read_byte()和pgm_read_word()中定义的宏{1}}访问数据结构。例如，您需要<avr/pgmspace.h>而不是main_menu.items。类似下面的示例 - 但请注意，此部分未经测试，可能包含拼写错误/ thinkos，尤其是在取消引用指针时：
pgm_read_byte(&(main_menu.items))在我看来，使用指针会使代码非常密集。一种完全不同的方法，一种使用数组索引来识别菜单，另一种方法来识别选项，对我来说似乎更为可取。