c++ - 编译器错误 : "does not name a type" in macro when compiling with g++

Question

我正在尝试创建一个宏来删除类的复制和移动构造函数。这段代码无法在 GCC 4.8.2 上用“编译。它有什么问题？如果我将所有内容放在一行中，代码就会编译。

#define DISALLOW_COPY_AND_MOVE(ClassName)                   \
    ClassName(const ClassName&) KEYWORD_DELETE;             \  // Copy constructor
    ClassName& operator=(const ClassName&) KEYWORD_DELETE;  \  // Copy assignment operator
    ClassName(ClassName &&) KEYWORD_DELETE;                 \  // Move constructor
    ClassName& operator=(ClassName&&) KEYWORD_DELETE;          // Move assignment operator

第二行不会发出编译器错误，但最后三行会。

KEYWORD_DELETE 只是:

#if defined CPP11
    #define KEYWORD_DELETE = delete
#else
    #define KEYWORD_DELETE
#endif // defined CPP11

这是输出:

In file included from ..\ObjectSlicing\src\main.cpp:5:0:
..\ObjectSlicing\src\__rm_utilities__/__rm_utilities__.h:26:5: error: stray '\' in program
     ClassName& operator=(const ClassName&) KEYWORD_DELETE;  \  // Copy assignment operator
     ^
..\ObjectSlicing\src\__rm_utilities__/__rm_utilities__.h:27:5: error: stray '\' in program
     ClassName(ClassName &&) KEYWORD_DELETE;                 \  // Move constructor
     ^
In file included from ..\ObjectSlicing\src\__include__/animals:5:0,
                 from ..\ObjectSlicing\src\main.cpp:6:
..\ObjectSlicing\src\__include__/../animals/cat.h:28:5: error: stray '\' in program
     DISALLOW_COPY_AND_MOVE(Cat)
     ^
In file included from ..\ObjectSlicing\src\__include__/animals:6:0,
                 from ..\ObjectSlicing\src\main.cpp:6:
..\ObjectSlicing\src\__include__/../animals/dog.h:28:5: error: stray '\' in program
     DISALLOW_COPY_AND_MOVE(Dog)
     ^
In file included from ..\ObjectSlicing\src\main.cpp:5:0:
..\ObjectSlicing\src\__rm_utilities__/__rm_utilities__.h:26:5: error: 'ClassName' does not name a type
     ClassName& operator=(const ClassName&) KEYWORD_DELETE;  \  // Copy assignment operator
     ^
..\ObjectSlicing\src\__rm_utilities__/__rm_utilities__.h:27:14: error: expected constructor, destructor, or type conversion before '(' token
     ClassName(ClassName &&) KEYWORD_DELETE;                 \  // Move constructor
              ^
..\ObjectSlicing\src\__rm_utilities__/__rm_utilities__.h:28:5: error: 'ClassName' does not name a type
     ClassName& operator=(ClassName&&) KEYWORD_DELETE;          // Move assignment operator
     ^

Answer 1

您没有发现错误:程序中出现杂散的“\”？

插入符号在错误的位置；它应该指向反斜杠:

..\ObjectSlicing\src\__rm_utilities__/__rm_utilities__.h:26:5: error: stray '\' in program
     ClassName& operator=(const ClassName&) KEYWORD_DELETE;  \  // Copy assignment operator
                                                             ^ -- here

你不能在反斜杠连续符后面加上 // 注释；如果您想在宏中嵌入注释，您需要使用 /* */ 注释并将它们放在 反斜杠之前。