序列化包含 std::string 的类 [英] Serializing a class which contains a std::string

问题描述

我不是 C++ 专家，但过去我已经将事情序列化了几次.不幸的是，这次我试图序列化一个包含 std::string 的类，我理解这很像序列化一个指针.

I'm not a c++ expert but I've serialized things a couple of times in the past. Unfortunately this time I'm trying to serialize a class which contains a std::string, which I understand is pretty much like serializing a pointer.

我可以将类写出到文件中，然后再读回.所有 int 字段都很好，但 std::string 字段给出了地址越界"错误，大概是因为它指向不再存在的数据.

I can write out the class to a file and read it back in again. All int fields are fine but the std::string field gives an "address out of bounds" error, presumably because it points to data which is no longer there.

对此有标准的解决方法吗?我不想回到字符数组，但至少我知道它们在这种情况下工作.如有必要，我可以提供代码，但我希望我已经很好地解释了我的问题.

Is there a standard workaround for this? I don't want to go back to char arrays but at least I know they work in this situation. I can provide code if necessary but I'm hoping I've explained my problem well.

我通过将类转换为 char* 并使用 fstream 将其写入文件来进行序列化.阅读当然正好相反.

I'm serializing by casting the class to a char* and writing it to a file with fstream. Reading of course is just the reverse.

推荐答案

我通过将类转换为 char* 并将其写入文件与 fstream.阅读当然正好相反.

I'm serializing by casting the class to a char* and writing it to a file with fstream. Reading of course is just the reverse.

不幸的是，这仅在不涉及指针时才有效.你可能想给你的类 void MyClass::serialize(std::ostream) 和 void MyClass::deserialize(std::ifstream)，然后调用它们.对于这种情况，您需要

Unfortunately, this only works as long as there are no pointers involved. You might want to give your classes void MyClass::serialize(std::ostream) and void MyClass::deserialize(std::ifstream), and call those. For this case, you'd want

std::ostream& MyClass::serialize(std::ostream &out) const {
    out << height;
    out << ',' //number seperator
    out << width;
    out << ',' //number seperator
    out << name.size(); //serialize size of string
    out << ',' //number seperator
    out << name; //serialize characters of string
    return out;
}
std::istream& MyClass::deserialize(std::istream &in) {
    if (in) {
        int len=0;
        char comma;
        in >> height;
        in >> comma; //read in the seperator
        in >> width;
        in >> comma; //read in the seperator
        in >> len;  //deserialize size of string
        in >> comma; //read in the seperator
        if (in && len) {
            std::vector<char> tmp(len);
            in.read(tmp.data() , len); //deserialize characters of string
            name.assign(tmp.data(), len);
        }
    }
    return in;
}

您可能还想重载流运算符以便于使用.

You may also want to overload the stream operators for easier use.

std::ostream &operator<<(std::ostream& out, const MyClass &obj)
{obj.serialize(out); return out;}
std::istream &operator>>(std::istream& in, MyClass &obj)
{obj.deserialize(in); return in;}

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