c++ - 带有 vector 结构的 boost::asio::buffer

Question

我有两个问题:

1. 在我的信息结构中，如果我有 float 或 double 类型而不是 std::string 它工作正常，但如果我使用 std::string 如下，在我的客户端部分我收到了结构，但之后它就崩溃了。

2. 我什至不能使用std::vector` 发送它，像这样:

---

struct info
{
    int id;
    std::string name;
};


int main(int argc, char** argv)
{

    boost::asio::io_service ios;
    boost::asio::ip::tcp::endpoint ep(boost::asio::ip::address::from_string("127.0.0.1"), 12345);
    boost::asio::ip::tcp::socket cl1(ios);

    cl1.open(ep.protocol());
    boost::system::error_code ec;
    cl1.connect(ep, ec);
    if (ec == 0)
        cout << "Connected" << endl;
    else {

        cout << "Not connected" << endl;
        system("pause");
        return -2;
    }

    info student;
    student.id = 7;
    student.name = "Rasul";

    cl1.send(boost::asio::buffer(&student, sizeof(student)));

    if (ec == 0)
        cout << "Written" << endl;
    else {

        cout << "Not written" << endl;
        system("pause");
        return -2;
    }
    cout << "Done" << endl;
    system("pause");
    return 0;
}

Answer 1

1. In my info structure if I have float or double types instead of std::string it works fine, but if I use std::string as below, in my client part i receive the struct but after that it just crashes.

那是因为float或double是POD数据类型而std::string不是，违反约定:

The boost::asio::buffer function is used to create a buffer object to represent raw memory, an array of POD elements, a vector of POD elements, or a std::string

准确地说，它们的意思是“POD元素的一个(数组| vector )]或[一个std::string]”，当你看看 list of overloads

添加一个静态断言，你会看到:

static_assert(std::is_pod<info>::value, "whoops, that can't work");
cl1.send(boost::asio::buffer(&student, sizeof(student)));

如果你想序列化它，你必须写一些代码。假设架构独立性和可移植性通常不是问题¹，您可以:

int32_t id_and_size[] = {student.id, static_cast<int32_t>(student.name.length())};
assert(id_and_size[1] >= 0); // because `size_t` is unsigned and larger than int32_t

cl1.send(boost::asio::buffer(id_and_size));
cl1.send(boost::asio::buffer(student.name.data(), student.name.length()));

这会发送与数据分开的长度:Live On Coliru]( http://coliru.stacked-crooked.com/a/897573028a86e16e )

00000000: 0700 0000 0500 0000 5261 7375 6c .......拉苏尔

虽然这很容易出错且乏味。如果你控制两端，考虑一个序列化框架(Boost Serialization，Google Protobuf ...)

¹ 因为您已经提到序列化 double 等的原始二进制形式