Copy structure with char array to char array [closed] - c++

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I have a problem as the topic.
My code:
struct message{
char sender_name[20];
char dest_name[20];
char content_message[256];
};
int main() {
message tmp;
printf("Enter your name\n");
std::cin>>tmp.sender_name;
printf("Enter dest name\n");
std::cin>>tmp.dest_name;
printf("Enter message to %s \n",tmp.dest_name);
std::cin>>tmp.content_message;
memcpy(&buffer, &tmp,sizeof(tmp));
printf("MEASAGE: %s\n",buffer);
return EXIT_SUCCESS;
}
In buffer is only tmp.sendername and I don't know how to fix it.
I read a lot of topics but I can't fix it.
Please for help.

Answer 1

It copies everything, you're just accessing it wrong:
#include <iostream>
#include <cstdlib>
#include <cstring>
using namespace std;
struct message{
char sender_name[20];
char dest_name[20];
char content_message[256];
};
char buffer[sizeof(message)];
int main() {
message tmp;
printf("Enter your name\n");
std::cin>>tmp.sender_name;
printf("Enter dest name\n");
std::cin>>tmp.dest_name;
printf("Enter message to %s \n",tmp.dest_name);
std::cin>>tmp.content_message;
memcpy(&buffer, &tmp,sizeof(tmp));
message *cpy = reinterpret_cast<message*>(buffer);
printf(
"sender_name: '%s\n'"
"dest_name: '%s\n'"
"content_message: '%s\n'",
cpy->sender_name,
cpy->dest_name,
cpy->content_message
);
return EXIT_SUCCESS;
}
Test:
g++ buffer.cc && printf '%s\n' foo bar baz | ./a.out
Output:
Enter your name
Enter dest name
Enter message to bar
sender_name: 'foo
'dest_name: 'bar
'content_message: 'baz
'
Also, BTW, probably not a good way to read into char buffers. There can hardly be any range checking with this API (given that it also appears to work with pointers as opposed to just arrays) which would make it about as unsafe as gets. It also doesn't appear to be documented (http://en.cppreference.com/w/cpp/io/basic_istream/operator_gtgt) and out of gcc and clang, only gcc accepts it.