Syntax and Sample Usage of _Generic in C11

Question

I heard C11 added generics. I've googled a bit, looked at some articles, understood there's a new keyword ( _Generic ) and all. But I can't seem to grasp it all.

Is it something like the generics in C# or templates in C++? Can anyone give me a brief explanation of the C11 definition of generics, its syntax and a simple sample usage example?

Answer 1

The best example I have seen inspired the following (runnable) example, which unlocks all sorts of freaky possibilities for cracked-out introspection...

#include <stdio.h> #include <stddef.h> #include <stdint.h>  #define typename(x) _Generic((x),        /* Get the name of a type */             \                                                                                   \         _Bool: "_Bool",                  unsigned char: "unsigned char",          \          char: "char",                     signed char: "signed char",            \     short int: "short int",         unsigned short int: "unsigned short int",     \           int: "int",                     unsigned int: "unsigned int",           \      long int: "long int",           unsigned long int: "unsigned long int",      \ long long int: "long long int", unsigned long long int: "unsigned long long int", \         float: "float",                         double: "double",                 \   long double: "long double",                   char *: "pointer to char",        \        void *: "pointer to void",                int *: "pointer to int",         \       default: "other")  #define fmt "%20s is '%s'\n" int main() {    size_t s; ptrdiff_t p; intmax_t i; int ai[3] = {0}; return printf( fmt fmt fmt fmt fmt fmt fmt fmt,       "size_t", typename(s),               "ptrdiff_t", typename(p),         "intmax_t", typename(i),      "character constant", typename('0'),  "0x7FFFFFFF", typename(0x7FFFFFFF),     "0xFFFFFFFF", typename(0xFFFFFFFF), "0x7FFFFFFFU", typename(0x7FFFFFFFU),  "array of int", typename(ai)); } 

                 ╔═══════════════╗  ═════════════════╣ Amazeballs... ╠═════════════════════════════════════                  ╚═══════════════╝              size_t is 'unsigned long int'          ptrdiff_t is 'long int'           intmax_t is 'long int' character constant is 'int'         0x7FFFFFFF is 'int'         0xFFFFFFFF is 'unsigned int'        0x7FFFFFFFU is 'unsigned int'       array of int is 'other'