比特币源码阅读(交易-COutPoint)

文档：https://en.bitcoin.it/wiki/Protocol_documentation

交易的输入是另外一笔交易的输出，它的结构如下图：

outpoint.png

对应的源码：

src/primitives/transaction.h

/** An outpoint - a combination of a transaction hash and an index n into its vout */
class COutPoint
{
public:
    uint256 hash; //out所在交易的hash
    uint32_t n; //所在索引

    COutPoint(): n((uint32_t) -1) { }
    COutPoint(const uint256& hashIn, uint32_t nIn): hash(hashIn), n(nIn) { }

    ADD_SERIALIZE_METHODS; //序列化

    template 
    inline void SerializationOp(Stream& s, Operation ser_action) {
        READWRITE(hash);
        READWRITE(n);
    }

    void SetNull() { hash.SetNull(); n = (uint32_t) -1; } //重置
    bool IsNull() const { return (hash.IsNull() && n == (uint32_t) -1); }

    friend bool operator<(const COutPoint& a, const COutPoint& b) //小于
    {
        int cmp = a.hash.Compare(b.hash);//这里hash判断大小有意义么?
        return cmp < 0 || (cmp == 0 && a.n < b.n);
    }

    friend bool operator==(const COutPoint& a, const COutPoint& b)//相等的条件
    {
        return (a.hash == b.hash && a.n == b.n);
    }

    friend bool operator!=(const COutPoint& a, const COutPoint& b) //不相等的条件
    {
        return !(a == b);
    }

    std::string ToString() const;
};