C++ 错误：“&”标记之前的预期初始化程序
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C++ error: expected initializer before ‘&’ token
提问by Open the way
the following piece of C++ code compiled two years ago in a suse 10.1 Linux machine.
以下是两年前在 suse 10.1 Linux 机器上编译的 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，我尝试在 Ubuntu 9.10 上编译它，但出现错误：
data.h:20: error: expected initializer before ‘&' token
which is referred to the line of:
这是指：
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提示吗？
Thanks
谢谢
P.D. If i do std::ostream, I get the errors:
PD 如果我执行 std::ostream，则会收到错误消息：
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'
回答by sbi
As everything in the C++ standard library, ostreamlives in the stdnamespace, so it's std::ostream.
因为一切都在C ++标准库，ostream住在std命名空间，所以它的std::ostream。
I believe that, if this used to compile, this was in error.
我相信，如果这用于编译，这是错误的。
回答by f4.
The ostreamclass is part of the C++ standard iostream library, and is defined in the namespace std
的ostream类是C ++标准iostream库的一部分，并在命名空间定义std
so you probably should add std::before ostream
or
所以你可能应该std::在ostream
或之前添加
using namespace std;
but, as stated in one of the comments :
但是，正如评论之一所述：
You should never use
using namespace stdin a header as it can propagate to other files.
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。
回答by Alexandre Hamez
You forgot to put std:: in front of each occurrence of ostream. Also, you should take Direction as a reference (while in this case, it won't hurt):
您忘记将 std:: 放在每次出现的ostream. 此外，您应该将方向作为参考（在这种情况下，它不会受到伤害）：
inline std::ostream& operator<<(std::ostream& os,const Direction& d)
回答by JBC--
you are missing a semicolon
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";
}
}`
