Question

我正在尝试序列化我班级的一些私人属性：

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;
};

serializeObject的定义如下：

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会返回很多错误：

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

我做错了什么？我跟随this示例。复制了商店功能并调整了一下。

Answer 1

Task::serializeObject()的返回值是fstream，而不是fstream&：这是尝试制作stream的副本，而流是不可复制的。来自std::ios_base::ios_base：

删除复制构造：stream不可复制

更改为：

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

注意我放弃了const因为我不确定为什么要这样做。

另外，这个：

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

不会按你的想法行事。 std::string将包含指向实际数据的指针，并且使用此实际数据不会写入stream。使用std::string::c_str()，可能使用std::string::length()，以便在重新阅读时知道字符串的长度。

fstream奇怪的行为

1 个答案: