Why does std::move cause SEGFAULT in this case?

April 27, 2022

#include <iostream>

struct Message {
    std::string message;
};

Message * Message_Init(std::string message) {
    Message * m = (Message*)calloc(1, sizeof(Message));
    m->message = std::move(message);
    return m;
}

int main() {
    auto m = Message_Init("Hello");
    return 0;
}

P.S. Please don’t ask why Message is not constructed in a usual C++ manner.

>Solution :

If you really want to do something like this, then you can use placement new. This allows you to construct an object in a chunk of memory that is already allocated.

Several of the standard containers use placement new to manage their internal buffers of objects.

However, it does add complications with the destructors of the objects you place. Read here for more info: What uses are there for "placement new"?

#include <iostream>
#include <memory>

struct Message {
    std::string message;
};

Message * Message_Init(std::string message) {
    void * buf = calloc(1, sizeof(Message));
    Message * m = new (buf) Message(); // placement new
    m->message = std::move(message);
    return m;
}

int main() {
    auto m = Message_Init("Hello");
    return 0;
}