I was coding a websocket class, and wanted to have a function as parameter in the constructor. But I forgot a : on the declaration of the message_handler method in the WebsocketClient class.
The compiler kept giving me this error:
error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'int'.
I was so confused but finally found the issue. But why does the compiler not tell me it can't resolve the type (which I guess was the issue because the syntax was wrong)?
This is the main code:
void ws_msg_handler(std::string &msg_recieved){
std::cout << "ws_msg_handler: " << msg_recieved << std::endl;
}
WebsocketClient wsClient("ws://my.secret.ip.adress:7777", ws_msg_handler);
This is the class:
class WebsocketClient {
private:
void message_handler(std:string &recieved_msg); // <- here is ":" missing
public:
char *uri;
WebsocketClient(char *uri, void (*message_handler)(std::string&)){
this->uri = uri;
this->message_handler = message_handler;
};
void ws_data_receive_handler(esp_websocket_event_data_t *data_recieved){
std::string msg_recieved(data_recieved->data_ptr);
this->message_handler(msg_recieved); // <- here it gives the error: "error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'int'"
}
};
I tried googling it, eventually asking ChatGPT. And when I gave the last piece of info, it was able to get out the syntax error.
why does the compiler not tell me it cant resolve the type?
It told you as first error, I got:
<source>:10:26: error: 'std' is not a type
10 | void message_handler(std:string &recieved_msg); // <- here is ":" missing
| ^~~
<source>:10:29: error: expected ',' or '...' before ':' token
10 | void message_handler(std:string &recieved_msg); // <- here is ":" missing
| ^
<source>: In member function 'void WebsocketClient::ws_data_receive_handler(esp_websocket_event_data_t*)':
<source>:15:31: error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'int'
15 | this->message_handler(msg_recieved); // <- here it gives the error: "error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'int'"
| ^~~~~~~~~~~~
| |
| std::string {aka std::__cxx11::basic_string<char>}
<source>:10:26: note: initializing argument 1 of 'void WebsocketClient::message_handler(int)'
10 | void message_handler(std:string &recieved_msg); // <- here is ":" missing
| ^~~
To allow to diagnose several errors, compiler has to "recover" from the previous errors. Replacing unknown/mal-formed types by int/void might be a method. This might lead to report future error "wrongly" though.
So you have to check for first error for accurate report.