Accessing return by pointer out of function - c++11

Question

I have the following function
std::tuple<int,val*>Socket::recv(val* values ) // const
{
char buf [ MAXRECV + 1 ];
memset ( buf, 0, MAXRECV + 1 );
int status = ::recv ( m_sock, buf, MAXRECV, 0 );
if ( status == -1 )
{
std::cout << "status == -1 errno == " << errno << " in Socket::recv\n";
// return std::make_tuple(0,NULL);//this is not working
}
else if ( status == 0 )
{
//return std::make_tuple(0,NULL); //this is not working
}
else
{
struct val* values=(struct val*) buf;
if(!std::isnan(values->val1) &&
!std::isnan(values->val2) &&
!std::isnan(values->val3) &&
!std::isnan(values->val4),
!std::isnan(values->val5),
!std::isnan(values->val6))
printf("received:%f %f %f %f %f %f\n", values->val1, values->val2,
values->val3, values->val4, values->val5, values->val6);
return std::make_tuple(status,values);
}
}
The received values are printed out in to standard output correctly within the function.
But when I try to access these received values out of the function by calling as follows what I get is all 0's.[after creating Socket rcvd object]
Would you tell me how to access these values outside the function?
1.
std::cout << std::get<1>(rcvd.recv(&values)->val1)
<< std::get<1>(rcvd.recv(&values)->val2)
<< std::get<1>(rcvd.recv(&values)->val3)
<< std::get<1>(rcvd.recv(&values)->val4)
<< std::get<1>(rcvd.recv(&values)->val5)
<< std::get<1>(rcvd.recv(&values)->val6)
<< std::endl;
2.
std::cout << std::get<1>(rcvd.recv(&values).val1)
<< std::get<1>(rcvd.recv(&values).val2)
<< std::get<1>(rcvd.recv(&values).val3)
<< std::get<1>(rcvd.recv(&values).val4)
<< std::get<1>(rcvd.recv(&values).val5)
<< std::get<1>(rcvd.recv(&values).val6)
<< std::endl;
3.
std::cout << std::get<1>(rcvd.recv(&values)[0])
<< std::get<1>(rcvd.recv(&values)[1])
<< std::get<1>(rcvd.recv(&values)[2])
<< std::get<1>(rcvd.recv(&values)[3])
<< std::get<1>(rcvd.recv(&values)[4])
<< std::get<1>(rcvd.recv(&values)[5])
<< std::endl;
where "values" comes from
struct val {
val1;
val2;
val3;
val4;
val5;
val6;} values;
All the three options of calling the function or access the struct val could not work for me.
Would you tell me
how to access these received values externally from any function?
how to return zero to struct pointer [NULL is not working ] when status is 0 or -1

Answer 1

Try
return std::make_tuple<int, val*>(0, nullptr);
The type of tuple is deduced from arguments, so by using 0,NULL you are actually using the null constant wich is evaluted to 0 and hence deduced type is <int,int>.
By the way, I see no reason for using NULL in C++11, if you need that really for some reason then cast NULL to val*
static_cast<val*>(NULL);
EDIT:
Other viable alternatives are
val* nullval = nullptr;
return std::make_tuple(0, nullval);
Or
return std::make_tuple(0, static_cast<val*>(nullptr));
Or (as comment suggest)
return {0, nullptr};
Choose the one that seems more clear to you.

Answer 2

You are lucky that the outside function is printing zeroes. It might have as well just dumped the core on you :)
What you are doing is accessing a buffer, that was created on a stack, after that stack was released (once the function's execution finished). That is HIGHLY UNSAFE and, pretty much, illegal.
Instead what you should do is allocate your data buffer in a 'free memory", using functions like malloc (in C) or operator new/new[] (in C++).
The quick fix is to replace the line
char buf [ MAXRECV + 1 ];
with
char * buf = new char [ MAXRECV + 1 ];
And when you do a type casting on line
struct val* values=(struct val*) buf;
you really ought to be sure that what you do is correct. If the sizeof() of you struct val is more than the sizeof(char[MAXRECV + 1]) you'll get in memory access troubles.
After you are done using the returned data buffer don't forget to release it with a call to free (in C) or delete/delete[] (in C++). Otherwise you'd have what is called a memory leak.