I have the following code in a C++ file:
#include <sys/socket.h>
// ...
void someFunc() {
struct msghdr msg = {0}; // <<< Uninitialized member here
}
When I compile with g++
using -Wall -Wextra
, I get warnings:
error: missing initializer for member 'msghdr::msg_namelen'
...same for several other fields
My problem is this: I can't explicitly initialize all the fields, because I don't know what fields will exist (cross-platform) in a struct msghdr
. The struct doesn't have a default constructor, since it's a C struct. I was under the impression that the = {0}
form led to zero-initialization of all fields (which would be fine for me), but the g++
error message suggests not.
What are my options here?
Structure members can be initialized using curly braces '{}'.
An initializer for a structure is a brace-enclosed comma-separated list of values, and for a union, a brace-enclosed single value. The initializer is preceded by an equal sign ( = ).
You don't have to initialise every element of a structure, but can initialise only the first one; you don't need nested {} even to initialise aggregate members of a structure. Anything in C can be initialised with = 0 ; this initialises numeric elements to zero and pointers null.
Different ways of initializing a variable in Cint a, b; a = b = 10; int a, b = 10, c = 20; Method 5 (Dynamic Initialization : Value is being assigned to variable at run time.)
void someFunc()
{
msghdr msg = {}; // <<< All members zero-initialized
}
The g++ -Wextra
warning level is IMHO not very useful.
The code that you have is also formally OK for a "C struct", in standardeese known as POD (Plain Old Data). But your code explicitly initializes first member with 0. That won't necessarily work for an aggregate that isn't POD, e.g. with a std::string
as first member, while the pure {}
will work also for that.
In passing, often a POD like the one you're dealing with has a byte count as first member, and then you can do like …
void foo()
{
SomePODStruct o = {sizeof(o)}; // The other members zero-initialized.
}
Perhaps add a STATIC_ASSERT
that the byte count member is first (at offset 0).
Cheers & hth.,
This should work:
memset(&msg, 0, sizeof(msg));
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With