测试函数时出现未知的解析错误

Question

我有下面的函数似乎应该正常运行，但是当通过测试程序运行程序时，我得到错误：解析错误：[int xSwapped =（（255＆lt;＆lt; nShift）|（ 255＆lt;＆lt; mShift））;]和 未声明的变量`xSwapped＆＃39;：[return（~xSwapped＆amp; x）| nMask | mmask指定;]

int dl15(int x, int n, int m){
        // calculates shifts, create mask to shift, combine result
        // get number of bytes needed to shift, multiplying by 8
        // get Masks by shifting 0xff and shift amount
        // shift bits to required position
        // combine results

        int nShift = n<< 3;
        int mShift = m<< 3;

        int nMask = x & (255 << nShift);
        int mMask = x & (255 << mShift);
        nMask = 255 & (nMask >> nShift);
        mMask = 255 & (mMask >> mShift);
        nMask = nMask << mShift;
        mMask = mMask << nShift;

        int xSwapped = ((255 << nShift) | (255 << mShift));

        return (~xSwapped & x) | nMask | mMask;

}

不确定我遗失了什么，谢谢。

Answer 1

看起来您正在使用C编译器设置为旧的C标准。在C99之前，您无法在声明之前放置可执行语句。

您可以通过将xSwapped的声明移到顶部来解决此问题：

int nShift = n<< 3;
int mShift = m<< 3;

int nMask = x & (255 << nShift);
int mMask = x & (255 << mShift);
int xSwapped;                                   // Declaration
nMask = 255 & (nMask >> nShift);
mMask = 255 & (mMask >> mShift);
nMask = nMask << mShift;
mMask = mMask << nShift;

xSwapped = ((255 << nShift) | (255 << mShift)); // Assignment

return (~xSwapped & x) | nMask | mMask;