# Define string (x) #x

const char * str = STRING(test _ STRING)； The content of str is "test_string", which means that # will put the symbol after it.

Add double quotation marks directly.

# # symbol connects two symbols to generate a new symbol (lexical hierarchy), for example:

# Define symbol (x) INT_##x

Int symbol (1); The macro will become: int int _1after expansion;