BewareMyPower commented on issue #6785:
URL: https://github.com/apache/pulsar/issues/6785#issuecomment-619524556
The C wrapper of `MessageId` has a `MessageId` field:
```c++
struct _pulsar_message_id {
pulsar::MessageId messageId;
};
```
And you can convert `std::string` to c-style string by:
```c++
char* string_to_raw_c_string(const std::string& s) {
char* c_str = static_cast<char*>(malloc(s.size() + 1));
memcpy(c_str, s.c_str(), s.size() + 1); // C++11 ensures that std::string
has a '\0' terminator
return c_str;
}
```
So you can implement the C functions like following code:
```c++
void pulsar_message_set_topic_name(pulsar_message_id_t *messageId, const
char* topicName) {
messageId->messageId->setTopicName(topicName);
}
char* pulsar_message_get_topic_name(pulsar_message_id_t *messageId) {
return string_to_raw_c_string(messageId->messageId->getTopicName());
}
```
Remind that the return value of `char*` must be freed. And use
`PULSAR_PUBLIC` to expose these C functions. I'm not familiar with cgo (we use
SWIG to wrap C++ client), it seems that it's convenient to convert between
`char*` and go string in cgo.
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