# Connector and # Operator in macro definition

# Connector and # Connector

# The Concatenation symbol is composed of two pound signs. Its function is to connect two substrings (tokens) in the macro definition with parameters to form a new substring. But it cannot be the first or last substring. The so-called token refers to the minimum syntax unit that the compiler can recognize. The specific definition has a detailed explanation in the compilation principle, but it does not matter if you do not know. At the same time, it is worth noting that the # operator replaces the passed parameters as strings. Let's take a look at how they work. This is an example on msdn.

Suppose the program has defined such a macro with parameters:

# Define Paster (n) printf ("token" # N "= % d", Token # N)

At the same time, an integer variable is defined:

Int token9 = 9;

Call this macro in the following way in the main program:

Paster (9 );

During compilation, the above sentence is extended:

Printf ("token" "9" "= % d", token9 );

Note that in this example, the "9" in Paster (9); is regarded as a string and connected with the "token", thus becoming the token9. # N is also replaced by "9.

As you can imagine, the result of running the program above is to print token9 = 9 on the screen.