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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 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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

Defined in header <math.h>
float atanhf( float arg );	(1)	(since C99)
double atanh( double arg );	(2)	(since C99)
long double atanhl( long double arg );	(3)	(since C99)
Defined in header <tgmath.h>
#define atanh( arg )	(4)	(since C99)

1-3) Computes the inverse hyperbolic tangent of arg.

4) Type-generic macro: If the argument has type long double, atanhl is called. Otherwise, if the argument has integer type or the type double, atanh is called. Otherwise, atanhf is called. If the argument is complex, then the macro invokes the corresponding complex function (catanhf, catanh, catanhl).

Parameters

arg	-	floating point value representing the area of a hyperbolic sector

Return value

If no errors occur, the inverse hyperbolic tangent of arg (tanh-1

(arg), or artanh(arg)), is returned.

If a domain error occurs, an implementation-defined value is returned (NaN where supported).

If a pole error occurs, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL is returned (with the correct sign).

If a range error occurs due to underflow, the correct result (after rounding) is returned.

Error handling

Errors are reported as specified in math_errhandling.

If the argument is not on the interval -1, +1, a range error occurs.

If the argument is ±1, a pole error occurs.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

if the argument is ±0, it is returned unmodified
if the argument is ±1, ±∞ is returned and FE_DIVBYZERO is raised.
if |arg|>1, NaN is returned and FE_INVALID is raised.
if the argument is NaN, NaN is returned

Notes

Although the C standard names this function "arc hyperbolic tangent", the inverse functions of the hyperbolic functions are the area functions. Their argument is the area of a hyperbolic sector, not an arc. The correct name is "inverse hyperbolic tangent" (used by POSIX) or "area hyperbolic tangent".

POSIX specifies that in case of underflow, arg is returned unmodified, and if that is not supported, an implementation-defined value no greater than DBL_MIN, FLT_MIN, and LDBL_MIN is returned.

Example

#include <stdio.h>#include <math.h>#include <float.h>#include <errno.h>#include <fenv.h>#pragma STDC FENV_ACCESS ON
int main(void){    printf("atanh(0) = %f\natanh(-0) = %f\n", atanh(0), atanh(-0.0));    printf("atanh(0.9) = %f\n", atanh(0.9));    //error handling
    errno = 0; feclearexcept(FE_ALL_EXCEPT);    printf("atanh(-1) = %f\n", atanh(-1));    if(errno == ERANGE) perror("    errno == ERANGE");    if(fetestexcept(FE_DIVBYZERO)) puts("    FE_DIVBYZERO raised");}

Possible output:

atanh(0) = 0.000000atanh(-0) = -0.000000atanh(0.9) = 1.472219atanh(-1) = -inf
    errno == ERANGE: Numerical result out of range
    FE_DIVBYZERO raised

References

C11 standard (ISO/IEC 9899:2011):

7.12.5.3 The atanh functions (p: 241)
7.25 Type-generic math <tgmath.h> (p: 373-375)
F.10.2.3 The atanh functions (p: 520)

C99 standard (ISO/IEC 9899:1999):

7.12.5.3 The atanh functions (p: 221-222)
7.22 Type-generic math <tgmath.h> (p: 335-337)
F.9.2.3 The atanh functions (p: 457)