[英]C++ error: expected initializer before ‘&’ token
the following piece of C++ code compiled two years ago in a suse 10.1 Linux machine. 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";
}
}
...
...
Now, I am trying to compile it on Ubuntu 9.10 and I get the error: 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
which is referred to the line of: 这是指以下行:
inline ostream& operator<<(ostream& os,const Direction d)
the g++ used on this machine is: 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)
Could you give me some hint about this error? 你能给我一些关于这个错误的暗示吗?
Thanks 谢谢
PD If i do std::ostream, I get the errors: 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’
As everything in the C++ standard library, ostream
lives in the std
namespace, so it's std::ostream
. 作为C ++标准库中的所有内容, ostream
存在于std
命名空间中,因此它是std::ostream
。
I believe that, if this used to compile, this was in error. 我相信,如果用于编译,这是错误的。
The ostream
class is part of the C++ standard iostream library, and is defined in the namespace std
ostream
类是C ++标准iostream库的一部分,在命名空间std
定义
so you probably should add std::
before ostream
所以你可能应该在ostream
之前添加std::
or 要么
using namespace std;
but, as stated in one of the comments : 但是,如其中一条评论所述:
You should never use
using namespace std
in a header as it can propagate to other files. 您永远不应该在标头中using namespace std
,因为它可以传播到其他文件。
You forgot to put std:: in front of each occurrence of ostream
. 你忘了把std ::放在每次出现的ostream
。 Also, you should take Direction as a reference (while in this case, it won't hurt): 此外,您应该将Direction作为参考(在这种情况下,它不会受到伤害):
inline std::ostream& operator<<(std::ostream& os,const Direction& d)
you are missing a semicolon 你错过了一个分号
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";
}
}`
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