stringWithCString：encoding：当输入的cstring包含表情符号时，返回nil

Question

Here is the story. I'm using a C lib for data transmission, and all work well except for certain Emoji. For the receiver, the received message is char *message , for which can use " printf " to print out the right thing. but when using stringWithCString:encoding: (or stringWithUTF8String: etc.), it return nil for certain emoji.

So, I print out each char, and here the successful emoji:

"\\xe2\\x9a\\xbd"

"\\xe2\\x9a\\xbe\\xef\\xb8\\x8f"

"\\xe2\\x98\\x81\\xef\\xb8\\x8f"

But the failed emoji:

"\\xed\\xa0\\xbc\\xed\\xbe\\x82"

"\\xed\\xa0\\xbc\\xed\\xbf\\x80"

"\\xed\\xa0\\xbc\\xed\\xbc\\x88"

have beening stuck on this days.

any ideas?

Thanks so much!!

Answer 1

It's because your bytes are not a valid UTF-8 encoded string. According to UTF-8 , "\\xed\\xa0\\xbc" encodes the Unicode code point U+D83C. This is a code point in the high surrogate block. Surrogates are not valid characters and are reserved for UTF-16 purposes. It is not valid for UTF-8 to encode such codepoints.