宏(#define)定义函数妙用

关于这宏定义函数的用法，现在不是特别常见，但是在特殊情况下还是很有用的。

定义如下：

class StringBuilder
{
public:
    StringBuilder(const char8_t* str);
    virtual ~StringBuilder();
    ...

    virtual StringBuilder& operator<<(const char8_t* value) { return operator+(value); }
    virtual StringBuilder& operator<<(int8_t value);
    virtual StringBuilder& operator<<(int16_t value);
    virtual StringBuilder& operator<<(int32_t value);
    virtual StringBuilder& operator<<(int64_t value);
    virtual StringBuilder& operator<<(uint8_t value);
    virtual StringBuilder& operator<<(uint16_t value);
    virtual StringBuilder& operator<<(uint32_t value);
    virtual StringBuilder& operator<<(uint64_t value);
    virtual StringBuilder& operator<<(double value);
    virtual StringBuilder& operator<<(const void * value);
};

基本实现思路如下, (代码十分简洁明了)

#define OPERATOR_IMPL(Type, Formatter) \
    StringBuilder& StringBuilder::operator<<(Type value) \
    { \
        if ((mSize - mCount) < 64) \
        { \
            if (!grow(64)) \
            { \
                mCount = 0; \
                return *this; \
            } \
        } \
        mCount += blaze_snzprintf(mBuffer + mCount, mSize - mCount, "%"Formatter, value); \
        return *this; \
    }

OPERATOR_IMPL(int8_t, PRId8);
OPERATOR_IMPL(int16_t, PRIi16);
OPERATOR_IMPL(int32_t, PRIi32);
OPERATOR_IMPL(int64_t, PRId64);
OPERATOR_IMPL(uint8_t, PRIu8);
OPERATOR_IMPL(uint16_t, PRIu16);
OPERATOR_IMPL(uint32_t, PRIu32);
OPERATOR_IMPL(uint64_t, PRIu64);
OPERATOR_IMPL(double, "f");
OPERATOR_IMPL(const void *, "p");

现在回头看看以前的总结http://jacky-dai.iteye.com/admin/blogs/868376,从这里可以看出有的时候宏定义函数还是很好用的。