Macro definition (GO)

Excerpt from: http://blog.chinaunix.net/uid-17188120-id-4026378.html

1. Simple macro definition

#define Identifier Substitution list (the replacement list can be number, string literal, punctuation, operator, identifier, keyword, character constant.) Note: The replacement list can be empty)

A typical use method:

The defined value is empty

#define BUG

Redefining data types

#define IT INT

2. Macros with parameters

#define Identifier (X1,X2,X3...XN) replacement list (note: x1,x2,x3. is a macro parameter, there cannot be a space between the identifier and its left parenthesis)

How to use:

#define MAX (x, y) > (y)? ( x):(y))

I=max (J+K,M-N);

To be replaced by:

I=max (J+k) > (m-n)? ( J+K):(m-n));

#define SI_EX (N) ((n)%2==0)

if (SI_EX (i)) i++;

To be replaced by:

if ((n)%2==0))

As we can see from the above example, identifiers with parameters (X1,x2,x3 ...). ) is replaced with a list (Y1,y2,y3 ...). ) corresponds to the substitution, but is not related to order.

Multi-line definition for 3.define

Define can replace multiple lines of code, adding a "\" to each line break

#define MAX (x, y) do {\

Statement 1; \

Statement 2; \

/* The notation of the comment */\

} while (0)/* (no trailing;) */\

4. In the large-scale development process, especially in cross-platform and system software, the most important function of define is conditional compilation.

#ifdef WINDOWS

......

#endif

#ifdef LINUX

......

#endif

Compile environment can be set by # define at compile time

5. Canceling a macro

#undef identifiers

6. Conditional compilation

#ifdef XXX ... (#else) ... #endif

Controls whether debug information is displayed

#ifdef Bugprint

#define BUG (ARG1,ARG2) printf (ARG1,ARG2)

#elif

#define BUG

#endif

7. Pre-defined macros

Some useful macros are included in the C language, which provide the current compilation information.

__line__ number of lines of compiled files

(Integral type)

__FILE__ the name of the compiled file (character type)

__date__ Compile date (character type)

__time__ compile time (character type)

__stdc__ if the compiler accepts standard C, then the value is 1. (Integral type)

Usually we compile with these predefined macros for troubleshooting purposes, such as:

In general, we can customize a workaround when the compiler is not prompted when a zero is present.

#define Checkzero (divisor) \

if (divisor==0) \

printf ("***attempt to DIVIDE by ZERO in line%d of file%s ***\n", __line__,__file__); \

Macro definition (GO)