C++错误:'&'标记之前的预期初始化程序

Question

两年前在一台suse 10.1 Linux机器上编译的以下C++代码.

#ifndef DATA_H
#define DATA_H
#include <iostream>
#include <iomanip>


inline double sqr(double x) { return x*x; }
enum   Direction { X,Y,Z };

inline Direction next(const Direction d)
{
  switch(d)
  {
  case X: return Y;
  case Y: return Z;
  case Z: return X;
  }
}

inline ostream& operator<<(ostream& os,const Direction d)
{
  switch(d)
  {
  case X: return os << "X";
  case Y: return os << "Y";
  case Z: return os << "Z";
  }
}
...
...

现在,我试图在Ubuntu 9.10上编译它,我得到错误:

data.h:20: error: expected initializer before ‘&’ token

这是指以下行:

inline ostream& operator<<(ostream& os,const Direction d)

这台机器上使用的g ++是:

Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.1-4ubuntu9' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --disable-werror --with-arch-32=i486 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu9) 

你能给我一些关于这个错误的暗示吗？

谢谢

PD如果我做std :: ostream,我得到错误:

data.h:20: error: declaration of ‘operator<<’ as non-function
data.h:20: error: ‘ostream’ was not declared in this scope
data.h:20: error: ‘os’ was not declared in this scope
data.h:20: error: expected primary-expression before ‘const’

Answer 1

作为C++标准库中的所有东西,都ostream存在于std命名空间中,所以它就是std::ostream.

我相信,如果用于编译,这是错误的.

Answer 2

的ostream类是C++标准iostream库的一部分,并在命名空间定义std

所以你可能应该在std::之前添加ostream
或

using namespace std;

但是,如其中一条评论所述:

您永远不应该using namespace std在标头中使用,因为它可以传播到其他文件.

Answer 3

你少了一个分号

inline Direction next(const Direction d)
{
   switch(d)
   {
     case X: return Y;
     case Y: return Z;
     case Z: return X;
   }
}**;**//missing semicolon

inline ostream& operator<<(ostream& os,const Direction d)
{
  switch(d)
  {
     case X: return os << "X";
     case Y: return os << "Y";
     case Z: return os << "Z";
  }
}`