编译器错误：使用g ++编译时，宏中没有“命名类型”

Question

我正在尝试创建一个宏来删除副本并移动类的构造函数。 这段代码无法在GCC 4.8.2上编译“。它有什么问题？如果我将所有内容放在一行上，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，但最后三行不会。

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

你没有发现error: stray '\\' in program ？

插入符号位于错误的位置; 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

你不能在反斜杠行继续符之后添加//注释; 如果你想在宏中嵌入注释，你需要使用/* */ comments并将它们放在反斜杠之前 。

Answer 2

另一个原因可能是：如果你正在使用类和朋友函数，并且如果你在你的朋友函数中调用了那个你在调用该函数之前就没有声明过的类-----喜欢：

#include <iostream>
using namespace std;
//class Second;
class first{

public:
    int val1;
    void setVal(int tval){
        val1=tval;
    }
    void display(){
        cout<<"in first value 1 is:"<<val1<<endl;
    }

    friend Second sum(first fobj,Second sobj);      
   };
  class Second{
  public:
  int val2;
    void setVal(int tval){
        val2=tval;
    }
    void display(){
        cout<<"in second value 2 is:"<<val2<<endl;
    }
    friend Second sum(first fobj,Second sobj);      
 };
Second sum(first fobj,Second sobj){
Second rel;
rel.val2=fobj.val1+sobj.val2;
return rel;
} 

int main(){
first f1;
Second s1;
f1.setVal(50);
s1.setVal(2);
f1.display();
s1.display();

Second rel=sum(f1,s1);
rel.display();
return 0;
}