目录搜索
AlgorithmsAlgorithms(算法)bsearchbsearch_sqsortqsort_sAtomic operationsAtomic operations library(原子操作库)ATOMIC_*_LOCK_FREEatomic_compare_exchange_strongatomic_compare_exchange_strong_explicitatomic_compare_exchange_weakatomic_compare_exchange_weak_explicitatomic_exchangeatomic_exchange_explicitatomic_fetch_addatomic_fetch_add_explicitatomic_fetch_andatomic_fetch_and_explicitatomic_fetch_oratomic_fetch_or_explicitatomic_fetch_subatomic_fetch_sub_explicitatomic_fetch_xoratomic_fetch_xor_explicitatomic_flagatomic_flag_clearatomic_flag_clear_explicitATOMIC_FLAG_INITatomic_flag_test_and_setatomic_flag_test_and_set_explicitatomic_initatomic_is_lock_freeatomic_loadatomic_load_explicitatomic_signal_fenceatomic_storeatomic_store_explicitatomic_thread_fence(线程围栏)ATOMIC_VAR_INITkill_dependencymemory_order(内存排序)C keywordsauto(自动存储)break(跳出循环)C keywords(关键词)casecharconst(常量修饰符)continuedefault(预设运算式)dodouble(双精度浮点型)elseenum(枚举类型)extern(全局变量)float(浮点数)forfortrangoto(goto语句)if(if语句)inline(行内函式)intlong(长整型)register(寄存器变量)restrict( restrict类型限定符)returnshortsignedsizeof(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_localC language#define directive#elif directive#else directive#endif directive#error directive#if directive#ifdef directive#ifndef directive#include directive#line directive#pragma directivealignas(对齐指定符)Alternative operators and tokens(替代运算符和令牌)AnalyzabilityArithmetic operatorsArithmetic typesArray declaration(数组声明)Array initialization(阵列初始化)ASCII ChartAssignment operators(赋值运算符)types(atomic类型限定符)Basic conceptsBit fields(位域)break statementC languageC Operator Precedencecast operatorcharacter 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 statementDeclarations(声明)do-while loopEnumerations(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 loopFunction declarations(函数声明)Function definitions(函数声明)FunctionsGeneric selection泛型选择goto statementIdentifier(标示符)if statementImplicit 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 constantLifetime(生命期)Logical operators(逻辑运算符)Lookup and name spacesMain function(主函式)Member access operators(会员接入运营商)Memory modelObjects and alignment(字节对齐)Order of evaluation(评估顺序)Other operatorsPhases of translation(翻译阶段)Pointer declarationPreprocessor(预处理)restrict type qualifier(restrict类型限定符)return statementScalar 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 statementThread storage duration(线程存储时间)TypeType(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 specifierDate and timeasctime(asctime函数)asctime_sclockCLOCKS_PER_SECclock_tctime(ctime函数)ctime_sDate and time utilities(日期和时间库)difftime(计算两个时间的间隔)gmtimegmtime_slocaltimelocaltime_smktime(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)timetimespectimespec_gettime_ttmwcsftime(格式化时间宽字符)Dynamic memory managementaligned_allocC memory management library(内存管理库)callocfree(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 handlingabort_handler_sassert(断言)constraint_handler_terrno(错误报告)Error handling(错误处理)Error numbers(错误个数)ignore_handler_sset_constraint_handler_sstatic_assertFile input/outputclearerr(清除/复位)fclosefeofferrorfflush(清空文件缓冲区)fgetcfgetposfgetsfgetwcfgetwsFile input/outputfopenfopen_sfprintffprintf_sfputcfputsfputwcfputwsfreadfreopenfreopen_sfscanffscanf_sfseekfsetposftellfwidefwprintffwprintf_sfwritefwscanffwscanf_sgetcgetchargetsgets_sgetwcharperrorprintfprintf_sputcputcharputsputwcputwcharremoverenamerewindscanfscanf_ssetbufsetvbufsnprintfsprintfsscanfsscanf_sswprintfswprintf_sswscanfswscanf_stmpfiletmpfile_stmpnamtmpnam_sungetcungetwcvfprintfvfprintf_svfscanfvfscanf_svfwprintfvfwprintf_svfwscanfvfwscanf_svprintfvprintf_svscanfvscanf_svsnprintfvsprintfvsscanfvsscanf_svswprintfvswprintf_svswscanfvswscanf_svwprintfvwprintf_svwscanfvwscanf_swprintfwprintf_swscanfwscanf_sLocalization supportlconvLC_ALLLC_COLLATELC_CTYPELC_MONETARYLC_NUMERICLC_TIMElocaleconvLocalization supportsetlocaleNumericsabsacosacosfacoshacoshfacoshlacoslasinasinfasinhasinhfasinhlasinlatanatan2atan2fatan2latanfatanhatanhfatanhlatanlcabscabsfcabslcacoscacosfcacoshcacoshfcacoshlcacoslcargcargfcarglcasincasinfcasinhcasinhfcasinhlcasinlcatancatanfcatanhcatanhfcatanhlcatanlcbrtcbrtfcbrtlccosccosfccoshccoshfccoshlccoslceilceilfceillcexpcexpfcexplcimagcimagfcimaglclogclogfcloglCMPLXCMPLXFCMPLXLCommon mathematical functionscomplexComplex number arithmeticconjconjfconjlcopysigncopysignfcopysignlcoscosfcoshcoshfcoshlcoslcpowcpowfcpowlcprojcprojfcprojlcrealcrealfcreallcsincsinfcsinhcsinhfcsinhlcsinlcsqrtcsqrtfcsqrtlctanctanfctanhctanhfctanhlctanldivdouble_terferfcerfcferfclerfferflexpexp2exp2fexp2lexpfexplexpm1expm1fexpm1lfabsfabsffabslfdimfeclearexceptfegetenvfegetexceptflagfegetroundfeholdexceptferaiseexceptfesetenvfesetexceptflagfesetroundfetestexceptfeupdateenvFE_ALL_EXCEPTFE_DFL_ENVFE_DIVBYZEROFE_DOWNWARDFE_INEXACTFE_INVALIDFE_OVERFLOWFE_TONEARESTFE_TOWARDZEROFE_UNDERFLOWFE_UPWARDFloating-point environmentfloat_tfloorfloorffloorlfmafmaffmalfmaxfmaxffmaxlfminfminffminlfmodfmodffmodlfpclassifyFP_INFINITEFP_NANFP_NORMALFP_SUBNORMALFP_ZEROfrexpfrexpffrexplHUGE_VALHUGE_VALFHUGE_VALLhypothypotfhypotlIilogbilogbfilogblimaginaryimaxabsimaxdivINFINITYisfiniteisgreaterisgreaterequalisinfislessislessequalislessgreaterisnanisnormalisunorderedlabsldexpldexpfldexplldivlgammalgammaflgammalllabslldivllrintllrintfllrintlllroundllroundfllroundlloglog10log10flog10llog1plog1pflog1pllog2log2flog2llogblogbflogbllogflogllrintlrintflrintllroundlroundflroundlMATH_ERREXCEPTmath_errhandlingMATH_ERRNOmodfmodffmodflnanNANnanfnanlnearbyintnearbyintfnearbyintlnextafternextafterfnextafterlnexttowardnexttowardfnexttowardlNumericspowpowfpowlPseudo-random number generationrandRAND_MAXremainderremainderfremainderlremquoremquofremquolrintrintfrintlroundroundfroundlscalblnscalblnfscalblnlscalbnscalbnfscalbnlsignbitsinsinfsinhsinhfsinhlsinlsqrtsqrtfsqrtlsrandtantanftanhtanhftanhltanltgammatgammaftgammaltrunctruncftrunclType-generic math_Complex_I_Imaginary_IProgram supportabortatexitat_quick_exitexitEXIT_FAILUREEXIT_SUCCESSgetenvgetenv_sjmp_buflongjmpProgram support utilitiesquick_exitraisesetjmpSIGABRTSIGFPESIGILLSIGINTsignalSIGSEGVSIGTERMsig_atomic_tSIG_DFLSIG_ERRSIG_IGNsystem_ExitStringsatofatoiatolatollbtowcc16rtombc32rtombchar16_tchar32_tisalnumisalphaisblankiscntrlisdigitisgraphislowerisprintispunctisspaceisupperiswalnumiswalphaiswblankiswcntrliswctypeiswdigitiswgraphiswloweriswprintiswpunctiswspaceiswupperiswxdigitisxdigitmblenmbrlenmbrtoc16mbrtoc32mbrtowcmbsinitmbsrtowcsmbsrtowcs_smbstate_tmbstowcsmbstowcs_smbtowcmemchrmemcmpmemcpymemcpy_smemmovememmove_smemsetmemset_sNull-terminated byte stringsNull-terminated multibyte stringsNull-terminated wide stringsstrcatstrcat_sstrchrstrcmpstrcollstrcpystrcpy_sstrcspnstrerrorstrerrorlen_sstrerror_sStrings librarystrlenstrncatThread supportcall_oncecnd_broadcastcnd_destroycnd_initcnd_signalcnd_timedwaitcnd_waitmtx_destroymtx_initmtx_lockmtx_plainmtx_recursivemtx_timedmtx_timedlockmtx_trylockmtx_unlockonce_flagONCE_FLAG_INITthrd_busythrd_createthrd_currentthrd_detachthrd_equalthrd_errorthrd_exitthrd_jointhrd_nomemthrd_sleepthrd_successthrd_timedoutthrd_yieldThread support librarythread_localtss_createtss_deleteTSS_DTOR_ITERATIONStss_gettss_setType supportBoolean type support libraryFixed width integer typesFLT_EVAL_METHODFLT_ROUNDSmax_align_tNULLNumeric limitsoffsetofptrdiff_tsize_tType supportVariadic functionsVariadic functionsva_argva_copyva_endva_listva_start
文字

在头文件<math.h>中定义



float       nextafterf( float from, float to );

(1)

(since C99)

double      nextafter( double from, double to );

(2)

(since C99)

long double nextafterl( long double from, long double to );

(3)

(since C99)

float       nexttowardf( float from, long double to );

(4)

(since C99)

double      nexttoward( double from, long double to );

(5)

(since C99)

long double nexttowardl( long double from, long double to );

(6)

(since C99)

Defined in header <tgmath.h>



#define nextafter(from, to)

(7)

(since C99)

#define nexttoward(from, to)

(8)

(since C99)

1-3)首先,将两个参数都转换为函数的类型,然后返回下一个可表示值from的方向to。如果from等于toto则返回。

4-6)首先,将第一个参数转换为函数的类型,然后返回下一个可表示值from的方向to。如果from等于toto则返回,转换long double为函数的返回类型,但不会丢失范围或精度。

7)类型 - 通用宏:如果任何参数具有类型long doublenextafterl则被调用。否则,如果任何参数具有整数类型或具有类型doublenextafter则被调用。否则,nextafterf被调用。

8)类型 - 通用宏:如果参数from具有类型long doublenexttowardl则被调用。否则,如果from有整数类型或类型doublenexttoward则调用。否则,nexttowardf被调用。

参数

from, to

-

浮点值

返回值

如果没有错误发生,下一个可表示值from的方向to。返回。如果from等于to,则to返回,转换为函数的类型。

如果范围误差由于发生溢出,±HUGE_VAL±HUGE_VALF,或±HUGE_VALL被返回(与相同的符号from)。

如果由于下溢而发生范围错误,则返回正确的结果。

错误处理

按照math_errhandling中的指定报告错误。

如果实现支持IEEE浮点运算(IEC 60559),

  • 如果from是有限的,但预期的结果是无穷大,提高FE_INEXACTFE_OVERFLOW

  • 如果from不相等to,结果是低于正常或零,则引发FE_INEXACTFE_UNDERFLOW

  • 在任何情况下,返回值都与当前舍入模式无关

  • 如果是from或者to是NaN,则返回NaN

笔记

POSIX指定溢出和下溢条件是范围错误(可能会设置错误)。

IEC 60559建议from每当返回from==to。这些函数会返回to,这会使零之间的行为保持一致:nextafter(-0.0, +0.0)返回+0.0nextafter(+0.0, -0.0)返回–0.0

#include <math.h>#include <stdio.h>#include <float.h>#include <fenv.h>
 int main(void){
    float from1 = 0, to1 = nextafterf(from1, 1);    printf("The next representable float after %.2f is %.20g (%a)\n", from1, to1, to1);
 
    float from2 = 1, to2 = nextafterf(from2, 2);    printf("The next representable float after %.2f is %.20f (%a)\n", from2, to2, to2);
 
    double from3 = nextafter(0.1, 0), to3 = 0.1;    printf("The number 0.1 lies between two valid doubles:\n"           "    %.56f (%a)\nand %.55f  (%a)\n", from3, from3, to3, to3); 
    // difference between nextafter and nexttoward:
    long double dir = nextafterl(from1, 1); // first subnormal long double
    float x = nextafterf(from1, dir); // first converts dir to float, giving 0    printf("Using nextafter, next float after %.2f (%a) is %.20g (%a)\n",
           from1, from1, x, x);
    x = nexttowardf(from1, dir);    printf("Using nexttoward, next float after %.2f (%a) is %.20g (%a)\n",
           from1, from1, x, x); 
    // special values    {
        #pragma STDC FENV_ACCESS ON        feclearexcept(FE_ALL_EXCEPT);
        double from4 = DBL_MAX, to4 = nextafter(from4, INFINITY);        printf("The next representable double after %.2g (%a) is %.23f (%a)\n",
               from4, from4, to4, to4);        if(fetestexcept(FE_OVERFLOW)) puts("   raised FE_OVERFLOW");        if(fetestexcept(FE_INEXACT)) puts("   raised FE_INEXACT");    } // end FENV_ACCESS block
 
    float from5 = 0.0, to5 = nextafter(from5, -0.0);    printf("nextafter(+0.0, -0.0) gives %.2g (%a)\n", to5, to5);}

输出:

The next representable float after 0.00 is 1.4012984643248170709e-45 (0x1p-149)The next representable float after 1.00 is 1.00000011920928955078 (0x1.000002p+0)The number 0.1 lies between two valid doubles:    0.09999999999999999167332731531132594682276248931884765625 (0x1.9999999999999p-4)and 0.1000000000000000055511151231257827021181583404541015625  (0x1.999999999999ap-4)Using nextafter, next float after 0.00 (0x0p+0) is 0 (0x0p+0)Using nexttoward, next float after 0.00 (0x0p+0) is 1.4012984643248170709e-45 (0x1p-149)The next representable double after 1.8e+308 (0x1.fffffffffffffp+1023) is inf (inf)
   raised FE_OVERFLOW
   raised FE_INEXACTnextafter(+0.0, -0.0) gives -0 (-0x0p+0)

参考

  • C11标准(ISO / IEC 9899:2011):

    • 7.12.11.3 nextafter函数(p:256)

    • 7.12.11.4 nexttoward函数(p:257)

    • 7.25类型通用数学<tgmath.h>(p:373-375)

    • F.10.8.3 nextafter函数(p:529)

    • F.10.8.4 nexttoward函数(p:529)

  • C99标准(ISO / IEC 9899:1999):

    • 7.12.11.3 nextafter函数(p:237)

    • 7.12.11.4 nexttoward函数(p:238)

    • 7.22类型通用数学<tgmath.h>(p:335-337)

    • F.9.8.3 nextafter函数(p:466)

    • F.9.8.4 nexttoward函数(p:466)

上一篇:下一篇: