X-Macros for Synchronized Definitions

Snippet

X-Macros for Synchronized Definitions

The X-Macro pattern is a powerful preprocessor technique used to maintain multiple related lists (like enums, strings, or switch cases) in sync. You define a list once and then 'apply' it by redefining the 'X' macro before each use. This prevents errors where an enum is updated but the corresponding string array is forgotten.

snippet.c
c
#define STATUS_LIST \
    X(IDLE, "System is waiting") \
    X(BUSY, "Processing task") \
    X(ERROR, "Fault detected")
 
// Generate Enum
typedef enum { 
    #define X(a, b) STATUS_##a, 
    STATUS_LIST 
    #undef X 
} status_t;
 
// Generate String Table
const char* status_msg[] = { 
    #define X(a, b) b, 
    STATUS_LIST 
    #undef X 
};

Breakdown

#define STATUS_LIST \

Defines the master list of items and their associated metadata.

X(IDLE, "System is waiting")

An entry in the list; X is a placeholder for a future macro.

#define X(a, b) STATUS_##a,

Redefines X to extract the first argument and append it to a prefix for the enum.

STATUS_LIST

Expands the master list using the current definition of X.

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X-Macros for Synchronized Definitions

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