# Define usage

1. Simple define Definition

# Deprecision MAX 1000

A simple max is defined. It represents 1000. If you write
For (I = 0; I {
................
}
The compiler replaces MAX with 1000 before processing this code.

2. define's "Function Definition"

Define can accept some parameters as the function does, as follows:

# Define max (x, y) (x)> (y )? (X) :( y );

This definition will return the big one in two numbers. Have you seen it? Because this "function" does not have a type check, it is like a function template. Of course, it is definitely not as secure as a template. It can be used as a simple template.

However, there are hidden risks. The example is as follows:
# Define Add (a, B) a + B;
In general use, there is no problem, but if you encounter problems such as: c * Add (a, B) * d, the purpose of the algebraic formula is that a + B is then multiplied by c and d, but because define is used (it is just a simple replacement), the formula is actually changed
C * a + B * d

Another example is as follows:
# Define pin (int *);
Pin a, B;
The intention is that a and B are both int-type pointers, but they actually become int * a, B;
A is an int pointer while B is an int variable.
This should use typedef instead of define, so that both a and B are int type pointers.

3. Single Row definition of macros
# Define A (x) T _ # x
# Define B (x) # @ x

# Define C (x) # x
Suppose: x = 1, there are:
A (1) ------> T_1
B (1) ------> 1
C (1) ------> "1"

(For more information, see hustli)

3. define multi-line Definition

Define can replace multiple lines of code, such as the macro definition in MFC (very classic, although disgusting)

# Define MACRO (arg1, arg2) do {
/* Declarations */
Stmt1;
Stmt2;
/*...*/
} While (0)/* (no trailing ;)*/
The key is to add a "," to each line feed without spaces.