C語言有哪些語法技巧和功能

C語言常常讓人覺得它所能表達(dá)的東西非常有限。它不具有類似第一級函數(shù)和模式匹配這樣的高級功能。但是C非常簡單，并且仍然有一些非常有用的語法技巧和功能，只是沒有多少人知道罷了。

int fibs[] = {1, 1, 2, 3, 5};

/* Entries may not correspond to actual numbers. Some entries omitted. */
#define EINVAL 1
#define ENOMEM 2
#define EFAULT 3
/* ... */
#define E2BIG 7
#define EBUSY 8
/* ... */
#define ECHILD 12
/* ... */

char *err_strings[] = {[0] = "Success",[EINVAL] = "Invalid argument",[ENOMEM] = "Not enough memory",[EFAULT] = "Bad address",/* ... */[E2BIG ] = "Argument list too long",[EBUSY ] = "Device or resource busy",/* ... */[ECHILD] = "No child processes"/* ... */};

struct point {int x;int y;int z;}

struct point p = {.x = 3, .y = 4, .z = 5};

#define FLAG_LIST(_) _(InWorklist) _(EmittedAtUses) _(LoopInvariant) _(Commutative) _(Movable) _(Lowered) _(Guard)

#define DEFINE_FLAG(flag) flag,enum Flag {None = 0,FLAG_LIST(DEFINE_FLAG)Total};#undef DEFINE_FLAG

enum Flag {None = 0,DEFINE_FLAG(InWorklist)DEFINE_FLAG(EmittedAtUses)DEFINE_FLAG(LoopInvariant)DEFINE_FLAG(Commutative)DEFINE_FLAG(Movable)DEFINE_FLAG(Lowered)DEFINE_FLAG(Guard)Total};

enum Flag {None = 0,InWorklist,EmittedAtUses,LoopInvariant,Commutative,Movable,Lowered,Guard,Total};

#define FLAG_ACCESSOR(flag) bool is##flag() const {return hasFlags(1 << flag);}void set##flag() {JS_ASSERT(!hasFlags(1 << flag));setFlags(1 << flag);}void setNot##flag() {JS_ASSERT(hasFlags(1 << flag));removeFlags(1 << flag);}FLAG_LIST(FLAG_ACCESSOR)#undef FLAG_ACCESSOR

/* Force a compilation error if condition is false, but also produce a result* (of value 0 and type size_t), so it can be used e.g. in a structure* initializer (or wherever else comma expressions aren't permitted). *//* Linux calls these BUILD_BUG_ON_ZERO/_NULL, which is rather misleading. */#define STATIC_ZERO_ASSERT(condition) (sizeof(struct { int:-!(condition); }) )#define STATIC_NULL_ASSERT(condition) ((void *)STATIC_ZERO_ASSERT(condition) )/* Force a compilation error if condition is false */#define STATIC_ASSERT(condition) ((void)STATIC_ZERO_ASSERT(condition))

STATIC_ASSERT(Total <= 32)

(void)sizeof(struct { int:-!(Total <= 32) })

(void)sizeof(struct { int: 0 })

(void)sizeof(struct { int: -1 } )