将unsigned int分配给结构中的数组枚举时的编译错误

Question

typedef struct {
uint64_t low;
uint64_t cache_size;
uint32_t range;
uint8_t cache;

/// Number of symbols in the tables
size_t count;

/// rc_encode()'s position in the tables
size_t pos;

/// Symbols to encode
enum {
    RC_BIT_0,
    RC_BIT_1,
    RC_DIRECT_0,
    RC_DIRECT_1,
    RC_FLUSH,
} symbols[RC_SYMBOLS_MAX];

/// Probabilities associated with RC_BIT_0 or RC_BIT_1
probability *probs[RC_SYMBOLS_MAX];

} lzma_range_encoder;

//Above is the structure.

//Below is the function

static inline void
rc_bit(lzma_range_encoder *rc, probability *prob, uint32_t bit)
{
rc->symbols[rc->count] = bit;      // problem code line 69
rc->probs[rc->count] = prob;
++rc->count;
}

//Error: error C2440: '=' : cannot convert from 'uint32_t' to 'lzma_range_encoder::' Conversion to enumeration type requires an explicit cast (static_cast, C-style cast or function-style cast)

'bit' is uint32_t which needs to be stored(type-casted) in lzma_range_encoder->symbols, but I am not able to do it somehow. tried every p&c. Also, searched earlier questions regarding this(static_cast and all but no luck)

It is a simple problem I guess. But I am stuck since 2 days. Please help. Thanks

Answer 1

Add a name to the enumeration:

enum symbol_enum
{
    // ...
} symbols[RC_SYMBOLS_MAX];

Then you can cast to it:

rc->symbols[rc->count] = static_cast<lzma_range_encoder::symbol_enum>(bit);

PS. In C++ you don't need to use typedef for structures or classes. The normal structure name can be used as-is.

Answer 2

You can use following thing with unnamed enum with C++11.

enum {
    RC_BIT_0,
    RC_BIT_1,
    RC_DIRECT_0,
    RC_DIRECT_1,
    RC_FLUSH,
} symbols[RC_SYMBOLS_MAX];

rc->symbols[rc->count] = 
static_cast<std::decay<std::decltype(*symbols)>::type>(bit);