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Algorithms Algorithms(算法) bsearch bsearch_s qsort qsort_s Atomic operations Atomic operations library(原子操作库) ATOMIC_*_LOCK_FREE atomic_compare_exchange_strong atomic_compare_exchange_strong_explicit atomic_compare_exchange_weak atomic_compare_exchange_weak_explicit atomic_exchange atomic_exchange_explicit atomic_fetch_add atomic_fetch_add_explicit atomic_fetch_and atomic_fetch_and_explicit atomic_fetch_or atomic_fetch_or_explicit atomic_fetch_sub atomic_fetch_sub_explicit atomic_fetch_xor atomic_fetch_xor_explicit atomic_flag atomic_flag_clear atomic_flag_clear_explicit ATOMIC_FLAG_INIT atomic_flag_test_and_set atomic_flag_test_and_set_explicit atomic_init atomic_is_lock_free atomic_load atomic_load_explicit atomic_signal_fence atomic_store atomic_store_explicit atomic_thread_fence(线程围栏) ATOMIC_VAR_INIT kill_dependency memory_order(内存排序) C keywords auto(自动存储) break(跳出循环) C keywords(关键词) case char const(常量修饰符) continue default(预设运算式) do double(双精度浮点型) else enum(枚举类型) extern(全局变量) float(浮点数) for fortran goto(goto语句) if(if语句) inline(行内函式) int long(长整型) register(寄存器变量) restrict( restrict类型限定符) return short signed sizeof(sizeof运算符) static(静态变量) struct(结构体) switch(switch语句) typedef(typedef关键字) union(联合体) unsigned(无符号) void(空类型) volatile(volatile变量) while(while语句) _Alignas _Alignof _Atomic _Bool _Complex _Generic _Imaginary _Noreturn _Static_assert _Thread_local C language #define directive #elif directive #else directive #endif directive #error directive #if directive #ifdef directive #ifndef directive #include directive #line directive #pragma directive alignas(对齐指定符) Alternative operators and tokens(替代运算符和令牌) Analyzability Arithmetic operators Arithmetic types Array declaration(数组声明) Array initialization(阵列初始化) ASCII Chart Assignment operators(赋值运算符) types(atomic类型限定符) Basic concepts Bit fields(位域) break statement C language C Operator Precedence cast operator character constant(字符字面量) Comments(注释符) Comparison operators(比较运算符) compound literals(符合字面量) Conditional inclusion(条件包含) Conformance(一致性) const type qualifier(const 限定符) Constant expressions(常量表达) continue statement Declarations(声明) do-while loop Enumerations(枚举类型) Escape sequences(转义字符) Expressions(表达式) External and tentative definitions(外部和暂定的定义) File scope(文件范围) floating constant(浮点常量) for loop Function declarations(函数声明) Function definitions(函数声明) Functions Generic selection泛型选择 goto statement Identifier(标示符) if statement Implicit conversions(隐式转换) Increment/decrement operators(前置/后置操作符) Initialization(初始化) inline function specifier(内联函式) integer constant Lifetime(生命期) Logical operators(逻辑运算符) Lookup and name spaces Main function(主函式) Member access operators(会员接入运营商) Memory model Objects and alignment(字节对齐) Order of evaluation(评估顺序) Other operators Phases of translation(翻译阶段) Pointer declaration Preprocessor(预处理) restrict type qualifier(restrict类型限定符) return statement Scalar initialization(标量类型初始化) Scope(范围) sizeof operator(sizeof运算符) Statements(陈述) static assert declaration(静态断言声明) Static storage duration(静态存储周期) Storage-class specifiers(存储类说明符) string literals(字符串字面量) Struct and union initialization(结构体与联合体初始化) Struct declaration(结构体声明) switch statement Thread storage duration(线程存储时间) Type Type(类型) Typedef declaration(Typedef声明) Undefined behavior(未定义行为) Union declaration(联合体声明) Value categories(值类别) Variadic arguments(变长参数宏) volatile type qualifier(volatile 类型限定符) while loop _Alignof operator _Noreturn function specifier Date and time asctime(asctime函数) asctime_s clock CLOCKS_PER_SEC clock_t ctime(ctime函数) ctime_s Date and time utilities(日期和时间库) difftime(计算两个时间的间隔) gmtime gmtime_s localtime localtime_s mktime(将时间结构数据转换成经过的秒数的函数) strftime(格式化输出时间函数) time timespec timespec_get time_t tm wcsftime(格式化时间宽字符) Dynamic memory management aligned_alloc C memory management library(内存管理库) calloc free(释放动态分配空间的函数) malloc(动态分配内存空间的函数) realloc(重新分配内存空间的函数) Error handling abort_handler_s assert(断言) constraint_handler_t errno(错误报告) Error handling(错误处理) Error numbers(错误个数) ignore_handler_s set_constraint_handler_s static_assert File input/output clearerr(清除/复位) fclose feof ferror fflush(清空文件缓冲区) fgetc fgetpos fgets fgetwc fgetws File input/output fopen fopen_s fprintf fprintf_s fputc fputs fputwc fputws fread freopen freopen_s fscanf fscanf_s fseek fsetpos ftell fwide fwprintf fwprintf_s fwrite fwscanf fwscanf_s getc getchar gets gets_s getwchar perror printf printf_s putc putchar puts putwc putwchar remove rename rewind scanf scanf_s setbuf setvbuf snprintf sprintf sscanf sscanf_s swprintf swprintf_s swscanf swscanf_s tmpfile tmpfile_s tmpnam tmpnam_s ungetc ungetwc vfprintf vfprintf_s vfscanf vfscanf_s vfwprintf vfwprintf_s vfwscanf vfwscanf_s vprintf vprintf_s vscanf vscanf_s vsnprintf vsprintf vsscanf vsscanf_s vswprintf vswprintf_s vswscanf vswscanf_s vwprintf vwprintf_s vwscanf vwscanf_s wprintf wprintf_s wscanf wscanf_s Localization support lconv LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME localeconv Localization support setlocale Numerics abs acos acosf acosh acoshf acoshl acosl asin asinf asinh asinhf asinhl asinl atan atan2 atan2f atan2l atanf atanh atanhf atanhl atanl cabs cabsf cabsl cacos cacosf cacosh cacoshf cacoshl cacosl carg cargf cargl casin casinf casinh casinhf casinhl casinl catan catanf catanh catanhf catanhl catanl cbrt cbrtf cbrtl ccos ccosf ccosh ccoshf ccoshl ccosl ceil ceilf ceill cexp cexpf cexpl cimag cimagf cimagl clog clogf clogl CMPLX CMPLXF CMPLXL Common mathematical functions complex Complex number arithmetic conj conjf conjl copysign copysignf copysignl cos cosf cosh coshf coshl cosl cpow cpowf cpowl cproj cprojf cprojl creal crealf creall csin csinf csinh csinhf csinhl csinl csqrt csqrtf csqrtl ctan ctanf ctanh ctanhf ctanhl ctanl div double_t erf erfc erfcf erfcl erff erfl exp exp2 exp2f exp2l expf expl expm1 expm1f expm1l fabs fabsf fabsl fdim feclearexcept fegetenv fegetexceptflag fegetround feholdexcept feraiseexcept fesetenv fesetexceptflag fesetround fetestexcept feupdateenv FE_ALL_EXCEPT FE_DFL_ENV FE_DIVBYZERO FE_DOWNWARD FE_INEXACT FE_INVALID FE_OVERFLOW FE_TONEAREST FE_TOWARDZERO FE_UNDERFLOW FE_UPWARD Floating-point environment float_t floor floorf floorl fma fmaf fmal fmax fmaxf fmaxl fmin fminf fminl fmod fmodf fmodl fpclassify FP_INFINITE FP_NAN FP_NORMAL FP_SUBNORMAL FP_ZERO frexp frexpf frexpl HUGE_VAL HUGE_VALF HUGE_VALL hypot hypotf hypotl I ilogb ilogbf ilogbl imaginary imaxabs imaxdiv INFINITY isfinite isgreater isgreaterequal isinf isless islessequal islessgreater isnan isnormal isunordered labs ldexp ldexpf ldexpl ldiv lgamma lgammaf lgammal llabs lldiv llrint llrintf llrintl llround llroundf llroundl log log10 log10f log10l log1p log1pf log1pl log2 log2f log2l logb logbf logbl logf logl lrint lrintf lrintl lround lroundf lroundl MATH_ERREXCEPT math_errhandling MATH_ERRNO modf modff modfl nan NAN nanf nanl nearbyint nearbyintf nearbyintl nextafter nextafterf nextafterl nexttoward nexttowardf nexttowardl Numerics pow powf powl Pseudo-random number generation rand RAND_MAX remainder remainderf remainderl remquo remquof remquol rint rintf rintl round roundf roundl scalbln scalblnf scalblnl scalbn scalbnf scalbnl signbit sin sinf sinh sinhf sinhl sinl sqrt sqrtf sqrtl srand tan tanf tanh tanhf tanhl tanl tgamma tgammaf tgammal trunc truncf truncl Type-generic math _Complex_I _Imaginary_I Program support abort atexit at_quick_exit exit EXIT_FAILURE EXIT_SUCCESS getenv getenv_s jmp_buf longjmp Program support utilities quick_exit raise setjmp SIGABRT SIGFPE SIGILL SIGINT signal SIGSEGV SIGTERM sig_atomic_t SIG_DFL SIG_ERR SIG_IGN system _Exit Strings atof atoi atol atoll btowc c16rtomb c32rtomb char16_t char32_t isalnum isalpha isblank iscntrl isdigit isgraph islower isprint ispunct isspace isupper iswalnum iswalpha iswblank iswcntrl iswctype iswdigit iswgraph iswlower iswprint iswpunct iswspace iswupper iswxdigit isxdigit mblen mbrlen mbrtoc16 mbrtoc32 mbrtowc mbsinit mbsrtowcs mbsrtowcs_s mbstate_t mbstowcs mbstowcs_s mbtowc memchr memcmp memcpy memcpy_s memmove memmove_s memset memset_s Null-terminated byte strings Null-terminated multibyte strings Null-terminated wide strings strcat strcat_s strchr strcmp strcoll strcpy strcpy_s strcspn strerror strerrorlen_s strerror_s Strings library strlen strncat Thread support call_once cnd_broadcast cnd_destroy cnd_init cnd_signal cnd_timedwait cnd_wait mtx_destroy mtx_init mtx_lock mtx_plain mtx_recursive mtx_timed mtx_timedlock mtx_trylock mtx_unlock once_flag ONCE_FLAG_INIT thrd_busy thrd_create thrd_current thrd_detach thrd_equal thrd_error thrd_exit thrd_join thrd_nomem thrd_sleep thrd_success thrd_timedout thrd_yield Thread support library thread_local tss_create tss_delete TSS_DTOR_ITERATIONS tss_get tss_set Type support Boolean type support library Fixed width integer types FLT_EVAL_METHOD FLT_ROUNDS max_align_t NULL Numeric limits offsetof ptrdiff_t size_t Type support Variadic functions Variadic functions va_arg va_copy va_end va_list va_start
文字

函数声明引入了一个指定函数的标识符,并且可选地指定函数参数的类型(原型)。函数声明(与定义不同)可能出现在块作用域和文件作用域中。

句法

在函数声明的声明语法中,可能由声明者修改的类型说明符序列指定返回类型(可以是除数组或函数类型之外的任何类型),声明符具有以下两种形式之一:

noptr-declarator ( parameter-list )

(1)


noptr-declarator ( identifier-list(optional) )

(2)


其中

noptr声明符

-

除unparenthesized指针声明符外的任何声明符。包含在此声明器中的标识符是成为函数标识符的标识符。

参数列表

-

无论是单个关键字void还是以逗号分隔的参数列表(可能以省略号参数结尾)

标识符表

-

逗号分隔的标识符列表(只有在该声明符被用作旧式函数定义的一部分时),对于不是定义的旧式声明,必须省略。

1)新式(C89)函数声明。该声明既引入了函数指示符本身,也作为未来函数调用表达式的函数原型,强制从参数表达式转换为声明的参数类型,并对参数个数进行编译时检查。

int max(int a, int b); // declarationint n = max(12.01, 3.14); // OK, conversion from double to int

2)旧式(K&R)功能声明。这个声明不像原型,任何未来的函数调用表达式都会执行默认的参数提升,并且如果参数的数量与参数的数量不匹配,将会调用未定义的行为。

int max();int n = max(true, (char)'a'); // calls max with two int args (after promotions)int n = max(12.01f, 3.14); // calls max with two double args (after promotions)int max(a, b) int a, b; { return a>b?a:b; } // definition expects ints; the second call is undefined

说明

函数的返回类型由声明符中的类型说明符确定,并可能在声明中像通常那样可能由声明器修改,这些类型必须是完整的非数组对象类型或类型void

void f(char *s); // return type is voidint sum(int a, int b); // return type of sum is int.int (*foo(const void *p))[3]; // return type is pointer to array of 3 int

函数声明符可以与其他声明符合在一起,只要它们可以共享它们的类型说明符和限定符。

int f(void), *fip(), (*pfi)(), *ap[3]; // declares two functions and two objectsinline int g(int), n; // error: inline qualifier is for functions onlytypedef int array_t[3];array_t a, h(); // error: array type cannot be a return type for a function

如果函数声明出现在任何函数之外,它引入的标识符具有文件范围和外部链接,除非static被使用或者以前的静态声明是可见的。如果声明发生在另一个函数中,则该标识符具有块范围(并且还有内部或外部链接)。

int main(void){ int f(int); // external linkage, file scope f(1); // definition needs to be available somewhere in the program}

声明中不是函数定义一部分的参数不需要命名:

int f(int, int); // declaration// int f(int, int) { return 7; } // Error, parameters must be named in definitions

参数列表中的每个参数都是引入单个变量的声明,并具有以下附加属性:

  • 声明符中的标识符是可选的(除非该函数声明是函数定义的一部分)

int f(int, double); // OKint g(int a, double b); // also OKint f(int, double) { return 1; } // Error: definition must name parameters
  • 唯一允许存在参数的存储类说明符是register,并且它在函数声明中被忽略,而非定义

int f(static int x); // Errorint f(int [static 10]); // OK (array index static is not a storage class specifier)
  • 数组类型的任何参数都会调整为相应的指针类型,如果数组声明符的方括号之间存在限定符(可能为C99)

int f(int[]); // declares int f(int*)int g(const int[10]); // declares int g(const int*)int h(int[const volatile]); // declares int h(int * const volatile)int x(int[*]); // declares int x(int*)
  • 函数类型的任何参数都会被调整为相应的指针类型

int f(char g(double)); // declares int f(char (*g)(double))int h(int(void)); // declares int h(int (*)(void))
  • 参数列表可能会终止, ...,详见可变参数函数。

int f(int, ...);
  • 参数不能有类型void(但可以有指向void的类型指针)。完全由关键字组成的特殊参数列表void用于声明不带参数的函数。

int f(void); // OKint g(void x); // Error
  • 出现在参数列表中的任何标识符都可以作为typedef名称或参数名称处理为 typedef 名称:int f(size_t,uintptr_t)被解析为函数的新样式声明器,该函数采用两个未命名的 size_t 和 uintptr_t 类型的参数,而不是一个旧式的声明器,它以一个名为 “size_t” 和 “uintptr_t” 的参数开始函数的定义。

  • 参数可能有不完整的类型,并可能使用 VLA 符号*(除了在函数定义中,数组间指针和函数指针调整后的参数类型必须完整)

有关函数调用机制的其他详细信息,请参阅函数调用运算符,然后返回以从函数返回。

笔记

不像在 C ++中,说明符f()f(void)具有不同的含义:该声明符f(void))是一种新的风格(原型)声明符声明一个函数,它没有参数。声明符f()是一种旧式(K&R)声明符,它声明了一个函数,该函数接受未指定数量的参数(除非在旧式函数定义中使用)。

int f(void); // declaration: takes no parametersint g(); // declaration: takes unknown parameters int main(void) { f(1); // compile-time error g(2); // undefined behavior} int f(void) { return 1; ) // actual definitionint g(a,b,c,d) int a,b,c,d; { return 2; } // actual definition

与函数定义不同,参数列表可以从 typedef 继承。

typedef int p(int q, int r); // p is a function type int(int, int)p f; // declares inf f(int, int)

在 C89中,说明符和限定符是可选的,如果省略,函数的返回类型默认为 int(可能由声明者修改)。* f(){//函数返回 int *返回NULL; }

(直到C99)

参考

  • C11 standard (ISO/IEC 9899:2011):

    • 6.7.6.3 Function declarators (including prototypes) (p: 133-136)

  • C99 standard (ISO/IEC 9899:1999):

    • 6.7.5.3 Function declarators (including prototypes) (p: 118-121)

  • C89/C90 standard (ISO/IEC 9899:1990):

    • 3.5.4.3 Function declarators (including prototypes)

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