在结构指针中查找值的地址

Question

I have a struct called message:

typedef unsigned char messageType;
struct message{
    message() : val(0), type(home),nDevice(0) {}
    messageType type;
    _int32 val;
    char nDevice;
};

And i have a pointer to that struct:

message* reply;

How can I get the address of reply.val so I can memcpy to it? eg:

    memcpy(inBuf+2,address here,4);

Answer 1

memcpy(inBuf+2, &reply->val, sizeof(reply->val));

will do because the precedence of -> is higher than address-of & .

If you are not sure about operator precedence, just use parenthesis, readability is more important:

memcpy(inBuf+2, &(reply->val), sizeof(reply->val));

Thanks for @DyP's comment, note that it's better to use sizeof(reply->val) than the literal 4 .

Answer 2

Try &(reply->val) .

Be aware that the compiler can add padding to structs which will potentially ruin your plan, however.

Answer 3

memcpy(&(reply->val), address, sizeof(address))