测试函数时出现未知的解析错误

Question

我有下面的函数，它似乎应该是这样，但是当通过测试程序运行程序时，我给出了错误：解析错误：[int xSwapped =（（255 < < nShift）|（255 < < mShift））;]和 未声明的变量`xSwapped'：[return（〜xSwapped & x）| nMask | mMask;]

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; 

} 

不确定我在想什么，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xSwapped声明移动到顶部解决此问题：

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;