fstream的怪異的行爲

我想我的序列化類的一些私有屬性：fstream的怪異的行爲

class Task { 
    public: 
     enum Status { COMPLETED, PENDIENT }; 
     // BLAH BLAH BLAH 
     // CLASS GETTERS SETTERS ETC... 
     const std::fstream serializeObject(std::fstream &stream); 
    private: 
     void setID(); 
     static int sCount; 
     int id; 
     std::string text; 
     Status status; 
     tm timestamp; 
};

的serializeObject這樣定義：

const std::fstream Task::serializeObject(std::fstream &stream) { 
    stream.write((char *) &id, sizeof(int)); 
    stream.write((char *) &text, sizeof(std::string)); 
    stream.write((char *) &status, sizeof(Status)); 
    stream.write((char *) &timestamp, sizeof(tm)); 
    return stream; 
}

GCC返回不少誤區：

In file included from /usr/include/c++/4.4/ios:39, 
       from /usr/include/c++/4.4/ostream:40, 
       from /usr/include/c++/4.4/iostream:40, 
       from task.cpp:1: 
/usr/include/c++/4.4/bits/ios_base.h: In copy constructor ‘std::basic_ios<char, std::char_traits<char> >::basic_ios(const std::basic_ios<char, std::char_traits<char> >&)’: 
/usr/include/c++/4.4/bits/ios_base.h:790: error: ‘std::ios_base::ios_base(const std::ios_base&)’ is private 
/usr/include/c++/4.4/iosfwd:47: error: within this context 
/usr/include/c++/4.4/iosfwd: In copy constructor ‘std::basic_fstream<char, std::char_traits<char> >::basic_fstream(const std::basic_fstream<char, std::char_traits<char> >&)’: 
/usr/include/c++/4.4/iosfwd:87: note: synthesized method ‘std::basic_ios<char, std::char_traits<char> >::basic_ios(const std::basic_ios<char, std::char_traits<char> >&)’ first required here 
/usr/include/c++/4.4/streambuf: In copy constructor ‘std::basic_filebuf<char, std::char_traits<char> >::basic_filebuf(const std::basic_filebuf<char, std::char_traits<char> >&)’: 
/usr/include/c++/4.4/streambuf:770: error: ‘std::basic_streambuf<_CharT, _Traits>::basic_streambuf(const std::basic_streambuf<_CharT, _Traits>&) [with _CharT = char, _Traits = std::char_traits<char>]’ is private 
/usr/include/c++/4.4/iosfwd:78: error: within this context 
/usr/include/c++/4.4/iosfwd: In copy constructor ‘std::basic_fstream<char, std::char_traits<char> >::basic_fstream(const std::basic_fstream<char, std::char_traits<char> >&)’: 
/usr/include/c++/4.4/iosfwd:87: note: synthesized method ‘std::basic_filebuf<char, std::char_traits<char> >::basic_filebuf(const std::basic_filebuf<char, std::char_traits<char> >&)’ first required here 
task.cpp: In member function ‘std::fstream Task::serializeObject(std::fstream&)’: 
task.cpp:104: note: synthesized method ‘std::basic_fstream<char, std::char_traits<char> >::basic_fstream(const std::basic_fstream<char, std::char_traits<char> >&)’ first required here

我在做什麼錯了？我遵循this的例子。複製了商店功能並適應了一下。

來源

2012-10-07 jviotti

除了已經提到的明顯問題（'std :: fstream'沒有拷貝構造函數），你應該用'std :: ostream'來實現你的serialize方法：你不需要嘗試從中讀取，在實現中也不需要特定的fjile流操作。因此，接收並返回一個'std :: ostream＆'可以使你的函數更加廣泛地適用。 –

通過返回std :: ostream＆獲得什麼優勢？像鏈接？你能解釋一下我的廣泛適用性嗎？謝謝:) – jviotti

是的，你會得到鏈接。 –

Task::serializeObject()的返回值是fstream而不是fstream&：這是試圖複製stream並且流是不可複製的。從std::ios_base::ios_base：

副本constuctor被刪除：流是不可拷貝

更改爲：

std::fstream& Task::serializeObject(std::fstream &stream)

注意我已經放棄了const因爲我不能確定爲什麼這將需要。

而且，這樣的：

stream.write((char *) &text, sizeof(std::string));

不會做你的想法。 A std::string將包含一個指向實際數據的指針，實際數據將不會被寫入stream。使用std::string::c_str()，可能與std::string::length()，因此重新讀取時字符串的長度是已知的。

來源

2012-10-07 21:28:38 hmjd

非常感謝！關於const，我讀的書推薦使用const來修改不會修改對象屬性的函數。糾正我，如果它是錯誤的:) – jviotti

關於將字符串寫入流，你的意思是這樣的：stream.write（（char *）text.c_str（），sizeof（text.length（）））;？ – jviotti

fstream的怪異的行爲

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