数组数组的指定初始化器

Question

我们可能知道 c99 中的 designated initializers 以及它们可用于初始化大型 const 数组的方式：

const int vals[] = {
    [0] = 10,
    [10] = 12
}

将vals 的索引0 初始化为10 并将vals 的索引10 初始化为12。

我的问题是如何将这种风格的指定初始化程序用于数组数组。这是我的示例代码：

typedef enum {
    COMMON = 0,
    STRINGS,
    KEY,
    PRECUSSIVE,
    GUITAR,
    KEYBOARD,
    BASS,
    PIANO,
    DRUMS,
    _INST_MAX
} instrument_classification_t;
static const int * const instrument_class_hierarchy[] = {
    [COMMON] = {STRINGS, KEY, PRECUSSIVE, _INST_MAX},
    [STRINGS] = {GUITAR, BASS, _INST_MAX},
    [KEY] = {PIANO, KEYBOARD, _INST_MAX},
    [PRECUSSIVE] = {DRUMS, _INST_MAX},
    [GUITAR] = NULL,
    [KEYBOARD] = NULL,
    [BASS] = NULL,
    [PIANO] = NULL,
    [DRUMS] = NULL
};

但我收到这些警告，暗示初始化仅使用第一个元素。

main.c:166:3: warning: braces around scalar initializer
   [COMMON] = {STRINGS, KEY, PRECUSSIVE, _INST_MAX},
   ^
main.c:166:3: note: (near initialization for 'instrument_class_hierarchy[0]')
main.c:166:15: warning: initialization makes pointer from integer without a cast [-Wint-conversion]
   [COMMON] = {STRINGS, KEY, PRECUSSIVE, _INST_MAX},
           ^
main.c:166:15: note: (near initialization for 'instrument_class_hierarchy[0]')
main.c:166:24: warning: excess elements in scalar initializer
   [COMMON] = {STRINGS, KEY, PRECUSSIVE, _INST_MAX},
                    ^
main.c:166:24: note: (near initialization for 'instrument_class_hierarchy[0]')
main.c:166:29: warning: excess elements in scalar initializer
   [COMMON] = {STRINGS, KEY, PRECUSSIVE, _INST_MAX},
                         ^
main.c:166:29: note: (near initialization for 'instrument_class_hierarchy[0]')
main.c:166:41: warning: excess elements in scalar initializer
   [COMMON] = {STRINGS, KEY, PRECUSSIVE, _INST_MAX},
                                     ^
main.c:166:41: note: (near initialization for 'instrument_class_hierarchy[0]')
main.c:167:3: warning: braces around scalar initializer
   [STRINGS] = {GUITAR, BASS, _INST_MAX},
   ^
main.c:167:3: note: (near initialization for 'instrument_class_hierarchy[1]')
main.c:167:16: warning: initialization makes pointer from integer without a cast [-Wint-conversion]
   [STRINGS] = {GUITAR, BASS, _INST_MAX},
            ^
main.c:167:16: note: (near initialization for 'instrument_class_hierarchy[1]')
main.c:167:24: warning: excess elements in scalar initializer
   [STRINGS] = {GUITAR, BASS, _INST_MAX},
                    ^
main.c:167:24: note: (near initialization for 'instrument_class_hierarchy[1]')
main.c:167:30: warning: excess elements in scalar initializer
   [STRINGS] = {GUITAR, BASS, _INST_MAX},
                          ^
main.c:167:30: note: (near initialization for 'instrument_class_hierarchy[1]')
main.c:168:3: warning: braces around scalar initializer
   [KEY] = {PIANO, KEYBOARD, _INST_MAX},
   ^
main.c:168:3: note: (near initialization for 'instrument_class_hierarchy[2]')
main.c:168:12: warning: initialization makes pointer from integer without a cast [-Wint-conversion]
   [KEY] = {PIANO, KEYBOARD, _INST_MAX},
        ^
main.c:168:12: note: (near initialization for 'instrument_class_hierarchy[2]')
main.c:168:19: warning: excess elements in scalar initializer
   [KEY] = {PIANO, KEYBOARD, _INST_MAX},
               ^
main.c:168:19: note: (near initialization for 'instrument_class_hierarchy[2]')
main.c:168:29: warning: excess elements in scalar initializer
   [KEY] = {PIANO, KEYBOARD, _INST_MAX},
                         ^
main.c:168:29: note: (near initialization for 'instrument_class_hierarchy[2]')
main.c:169:3: warning: braces around scalar initializer
   [PRECUSSIVE] = {DRUMS, _INST_MAX},
   ^
main.c:169:3: note: (near initialization for 'instrument_class_hierarchy[3]')
main.c:169:19: warning: initialization makes pointer from integer without a cast [-Wint-conversion]
   [PRECUSSIVE] = {DRUMS, _INST_MAX},
               ^
main.c:169:19: note: (near initialization for 'instrument_class_hierarchy[3]')
main.c:169:26: warning: excess elements in scalar initializer
   [PRECUSSIVE] = {DRUMS, _INST_MAX},

Answer 1

花括号的值列表不能初始化指针。您的错误与以下相同：

int *p = { 1, 2, 3 };

您可以改用复合文字：

// ...
[COMMON] = (const int[]){STRINGS, KEY, PRECUSSIVE, _INST_MAX},

这假定代码在文件范围内（即在任何函数之外），这意味着复合文字具有静态存储持续时间，因此指向它们是安全的。如果您的代码实际上是在函数内部，则需要声明单独的静态数组或进行一些其他修改。