Why I get error on string concatination?

Question

exit status 1 invalid operands of types 'const char [5]' and 'const char [2]' to binary 'operator+'

 String message = "Page not found\n\n";
 message += "URI: " + HTTP.uri() + "\n";
 message += "Method: " + (HTTP.method() == HTTP_GET)? "GET": "POST" + "\n";
 message += "Arguments: " + HTTP.args() + "\n";

• Chad G: which line is it having problems with?
• jsotola: try enclosing the ternary operator in brackets ((HTTP.method() == HTTP_GET)? "GET": "POST")

Answer 1

The operators of the class String apply only for an instance of String. In your expression you concatenate two c-strings "POST" + "\n"

Answer 2

A simple fix is to just move the (const char *)s around a little:

This should compile

 String message = "Page not found\n\n";
 message += "URI: " + HTTP.uri() + "\n";
 message += "Method: " + (HTTP.method() == HTTP_GET)? "GET\n": "POST\n";
 message += "Arguments: " + HTTP.args();
 message += "\n";