Protobuf C++ message with google timestamp leads to seg fault

Question

I am new to using google protobuffers and I created a basic message:

message msg {  
    uint32 id = 1;                             
    google.protobuf.Timestamp timestamp = 2;  
}

Now I created a small c++ program to use this [with the necessary headers]

int main(void) {
  auto m = msg{};
  m.set_id(2);
  auto timestamp = google::protobuf::Timestamp{};
  timestamp.set_seconds(time(NULL));
  timestamp.set_nanos(0);

  m.set_allocated_timestamp(&timestamp);

  std::cout << m.id() << std::endl;
  std::cout << m.timestamp().seconds() << std::endl;

  return 0;
}

However, this program gives a seg fault.

free(): invalid pointer
[1]    9537 abort (core dumped)

where do I need to release memory?

Offtopic: `timestamp.set_seconds(time(NULL));` is also undefined behavior. No risk of crash, just you do not have a warranty that `time` returns seconds. — Marek R, Jul 15 '19 at 15:17
timestamp.set_seconds(time(NULL)); comes from the official protocol buffer site https://developers.google.com/protocol-buffers/docs/reference/google.protobuf#google.protobuf.Timestamp but obviously I am open to better suggestions. — Mike, Jul 15 '19 at 15:24
@MarekR for all intents and purposes, you do have this guarantee. — SergeyA, Jul 15 '19 at 15:34

SergeyA · Accepted Answer · 2019-07-15T15:32:42.207

5

A protobuf's set_allocated_foo() function will take ownership of the pointer and attempt to free it after message itself runs out of scope. See more at https://developers.google.com/protocol-buffers/docs/reference/cpp-generated

Since your pointer points to the automatic object, attempt at deleting this pointer yields undefined behavior, in your case, a coredump.

To set protobuf's TimeStamp, you first have to obtain a pointer to it using mutable_timestamp, and than you can set it's individual fields.

edited Jul 15 '19 at 15:32

answered Jul 15 '19 at 15:16

SergeyA

61,605
5
78
137

Unfortunately, there is no set_timestamp. I used set_allocated_timestamp as I could not find another set method to my surprise. So my actual question here is more: How do I set timestamp in a message – Mike Jul 15 '19 at 15:25
Then you have to `new` it instead of using an automatic object. – Goswin von Brederlow Jul 15 '19 at 15:29
@Mike my bad. Timestamp is a message on it's own. Fixed the answer. – SergeyA Jul 15 '19 at 15:32
1

... auto timestamp = new google::protobuf::Timestamp{}; timestamp->set_seconds(time(NULL)); timestamp->set_nanos(0); e.set_allocated_timestamp(timestamp); ... indeed fixes the problem. – Mike Jul 15 '19 at 15:35

Protobuf C++ message with google timestamp leads to seg fault

1 Answers1