编译时检查是否所有数组成员都已初始化

Question

假设我声明了一个固定大小的数组并初始化了它的成员。有没有办法在编译时检查所有成员是否都已初始化，这样我就可以避免由于未初始化值而导致的错误？这是我正在处理的示例:

enum image_format {
    IMAGE_FORMAT_UBI = 0,
    IMAGE_FORMAT_BOOT,
    IMAGE_FORMAT_RAW,
    _IMAGE_FORMAT_LAST
};

#define IMAGE_FORMAT_COUNT (_IMAGE_FORMAT_LAST - IMAGE_FORMAT_UBI)

static int image_format_validator_ubi(const char *filename);
static int image_format_validator_boot(const char *filename);

typedef int (*image_format_validator)(const char *filename);

static image_format_validator image_format_validators[IMAGE_FORMAT_COUNT] = {
    [IMAGE_FORMAT_UBI]  = &image_format_validator_ubi,
    [IMAGE_FORMAT_BOOT] = &image_format_validator_boot,
    [IMAGE_FORMAT_RAW]  = NULL
};

在这种情况下，我想检查 IMAGE_FORMAT_COUNT 数量的元素在 image_format_validators 数组中被初始化。

Answer 1

Is there a way to check at compile time, if all members were initialized (?)

C 中没有部分初始化，它是全有或全无。未显式初始化的元素将使用默认值进行初始化。

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为了帮助检测 image_format_validators[] 是否为预期大小，一种方法使用 _Static_assert(constant-expression , string-literal)。如果 constant-expression 不等于 0，则一切正常。否则“实现应产生包含字符串文字文本的诊断消息” C11 §6.7.10 3

enum image_format {
    IMAGE_FORMAT_UBI = 0,
    IMAGE_FORMAT_BOOT,
    IMAGE_FORMAT_RAW,
    IMAGE_FORMAT_N
};

//                                                    v--- empty
static image_format_validator image_format_validators[ ] = {
    [IMAGE_FORMAT_UBI]  = &image_format_validator_ubi,
    [IMAGE_FORMAT_BOOT] = &image_format_validator_boot,
    [IMAGE_FORMAT_RAW]  = NULL
};

#define IFV_N (sizeof image_format_validators/sizeof image_format_validators[0])
_Static_assert(IFV_N == IMAGE_FORMAT_N, "Unexpected size");

以上内容仍然可能被愚弄，但确实可以很好地确保映射到数组的顺序枚举类型具有预期的 N 个数组元素。

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如果不使用 C11，请参阅编译时检查备选方案:C_ASSERT(expr) .