您的代码似乎是正确的。

Your code seems to be correct.

以下程序（ http://ideone.com/a5TBF ） ：

#include <cstdio>

inline unsigned int endian_swap(unsigned const int& x)  
{
return ( ( (x & 0x000000FF) << 24 ) | 
         ( (x & 0x0000FF00) << 8  ) |
         ( (x & 0x00FF0000) >> 8  ) |
         ( (x & 0xFF000000) >> 24 ) );
}

int main()
{
    unsigned int x = 0x12345678;
    unsigned int y = endian_swap(x);
    printf("%x %x\n", x, y);
    return 0;
}

输出：

12345678 78563412

12345678 78563412

编辑：

你需要 std :: cout<< std :: hex<< r

you need std::cout << std::hex << r, otherwise you are printing (1) wrong variable, and (2) in decimal :-)

查看此示例： http://ideone.com/EPFz8