c++ - C++中异常类的继承

Question

我正在用 C++ 编写一些继承自基类的异常类，但我不明白为什么它无法编译。任何帮助，将不胜感激。

基类: RandomAccessFileException.h

#ifndef RANDOMACCESSFILEEXCEPTION_H
#define RANDOMACCESSFILEEXCEPTION_H

class RandomAcessFileException
{
public:
    RandomAcessFileException();
    virtual const char* getMessage() = 0;
protected:
    char m_message[100];
};

#endif

派生类: RandomAccessFileNotFoundException.h

#ifndef RANDOMACCESSFILENOTFOUNDEXCEPTION_H
#define RANDOMACCESSFILENOTFOUNDEXCEPTION_H

#include "RandomAccessFileException.h"

class RandomAccessFileNotFoundException : public RandomAccessFileException
{
public:
    RandomAccessFileNotFoundException(const char* p_filename);
    const char* getMessage();
};

#endif

RandomAccessFileNotFoundException.cpp

#include <cstring>

#include "RandomAccessFileException.h"
#include "RandomAccessFileNotFoundException.h"

RandomAccessFileNotFoundException::RandomAccessFileNotFoundException(const char* p_filename)
{
    strcat(m_message, "RandomAccessFileNotFoundException: File: ");
    strcat(m_message, p_filename);
}

const char* RandomAccessFileNotFoundException::getMessage()
{
    return m_message;
}

g++ 说:

在 RandomAccessFileNotFoundException.cpp:4:0 包含的文件中: RandomAccessFileNotFoundException.h:13:1: 错误:“{”标记前的预期类名 RandomAccessFileNotFoundException.cpp:在构造函数“RandomAccessFileNotFoundException::RandomAccessFileNotFoundException(const char*)”中: RandomAccessFileNotFoundException.cpp:8:12: 错误:“m_message”未在此范围内声明 RandomAccessFileNotFoundException.cpp:在成员函数‘const char* RandomAccessFileNotFoundException::getMessage()’中: RandomAccessFileNotFoundException.cpp:14:12: 错误:“m_message”未在此范围内声明

Answer 1

第一个问题:

你必须:

#include "RandomAccessFileException.h"

在您的 RandomAccessFileNotFoundException.h 头文件中，因为它包含 RandomAccessFileNotFoundException 基类的定义(即 RandomAccessFileException)。

总而言之，您的头文件 RandomAccessFileNotFoundException.h 头应该是:

#ifndef RANDOMACCESSFILENOTFOUNDEXCEPTION_H
#define RANDOMACCESSFILENOTFOUNDEXCEPTION_H

#include "RandomAccessFileException.h"

class RandomAccessFileNotFoundException : public RandomAccessFileException
//                                               ^^^^^^^^^^^^^^^^^^^^^^^^^
//                                               This class is defined in the
//                                               RandomAccessFileException.h
//                                               header, so you have to #include
//                                               that header before using this
//                                               class as a base class.
{
public:
    RandomAccessFileNotFoundException(const char* p_filename);
    const char* getMessage();
};

#endif

第二个问题:

另请注意，您有错别字。您的基类称为:

RandomAcessFileException
//     ^

代替:

RandomAccessFileException
//     ^^

这是您在 RandomAccessFileException.h 中使用的名称。

第三个问题:

最后，您缺少基类的 (RandomAccessFile) 构造函数的定义，您只为其提供了一个声明:

class RandomAcessFileException
{
public:
    RandomAcessFileException();
//  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
//  This is a DECLARATION of the constructor, but the definition is missing
    virtual const char* getMessage() = 0;
protected:
    char m_message[100];
};

如果不提供定义，链接器将发出 Unresolved 引用错误。