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
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在头文件<ctype.h>中定义 | ||
|---|---|---|
int islower（int ch）; |
根据当前C语言环境检查给定字符是否被分类为小写字符。在默认的“C”语言环境中，islower仅对小写字母（abcdefghijklmnopqrstuvwxyz）返回true 。
如果islower返回true，则确保iscntrl，isdigit，ispunct和isspace在同一个C语言环境中为同一个字符返回false。
如果ch的值不能表示为unsigned char并且不等于EOF，则行为是未定义的。
参数
ch | - | 字符分类 |
|---|
返回值
如果字符是小写字母，则为非零值，否则为零。
例
#include <stdio.h>#include <ctype.h>#include <locale.h>
int main(void){
unsigned char c = '\xe5'; // letter å in ISO-8859-1 printf("In the default C locale, \\xe5 is %slowercase\n", islower(c) ? "" : "not " ); setlocale(LC_ALL, "en_GB.iso88591"); printf("In ISO-8859-1 locale, \\xe5 is %slowercase\n", islower(c) ? "" : "not " );}输出：
In the default C locale, \xe5 is not lowercase In ISO-8859-1 locale, \xe5 is lowercase
参考
C11标准（ISO / IEC 9899：2011）：
7.4.1.7 islower函数（p：202）
C99标准（ISO / IEC 9899：1999）：
7.4.1.7 islower函数（p：183）
C89 / C90标准（ISO / IEC 9899：1990）：
4.3.1.6 islower函数
扩展内容
iswlower（C95） | 检查宽字符是否是小写字符（函数） |
|---|
| 用于islower的C ++文档 |
ASCII 值 (十六进制) | 字符 | iscntrl iswcntrl. | isprint iswprint. | isspace iswspace. | isblank iswblank. | isgraph iswgraph. | ispunct iswpunct. | isalnum iswalnum. | isalpha iswalpha. | isupper iswupper. | islower iswlower. | isdigit iswdigit. | isxdigit iswxdigit. | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0 - 8 | 0x00-0x08 | 控制码 (NUL, etc.) | ≠0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
9 | 0x09 | tab (\t) | ≠0 | 0 | ≠0 | ≠0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
10 - 13 | 0x0A-0x0D | 空格 (\n,\v,\f,\r) | ≠0 | 0 | ≠0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
14 - 31 | 0x0E-0x1F | 控制码 | ≠0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
32 | 0x20 | space | 0 | ≠0 | ≠0 | ≠0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
33 - 47 | 0x21-0x2F | !"#$%&'()*+,-./ | 0 | ≠0 | 0 | 0 | ≠0 | ≠0 | 0 | 0 | 0 | 0 | 0 | 0 |
48 - 57 | 0x30-0x39 | 0123456789 | 0 | ≠0 | 0 | 0 | ≠0 | 0 | ≠0 | 0 | 0 | 0 | ≠0 | ≠0 |
58 - 64 | 0x3a-0x40 | :;<=>?@ | 0 | ≠0 | 0 | 0 | ≠0 | ≠0 | 0 | 0 | 0 | 0 | 0 | 0 |
65 - 70 | 0x41-0x46 | ABCDEF | 0 | ≠0 | 0 | 0 | ≠0 | 0 | ≠0 | ≠0 | ≠0 | 0 | 0 | ≠0 |
71 - 90 | 0x47-0x5A | GHIJKLMNOPQRSTUVWXYZ | 0 | ≠0 | 0 | 0 | ≠0 | 0 | ≠0 | ≠0 | ≠0 | 0 | 0 | 0 |
91 - 96 | 0x5B-0x60 | []^_` | 0 | ≠0 | 0 | 0 | ≠0 | ≠0 | 0 | 0 | 0 | 0 | 0 | 0 | | ||||||||||||
97 -102 | 0x61-0x66 | abcdef | 0 | ≠0 | 0 | 0 | ≠0 | 0 | ≠0 | ≠0 | 0 | ≠0 | 0 | ≠0 |
103-122 | 0x67-0x7A | ghijklmnopqrstuvwxyz | 0 | ≠0 | 0 | 0 | ≠0 | 0 | ≠0 | ≠0 | 0 | ≠0 | 0 | 0 |
123-126 | 0x7B-0x7E | {|}~ | 0 | ≠0 | 0 | 0 | ≠0 | ≠0 | 0 | 0 | 0 | 0 | 0 | 0 |
127 | 0x7F | 退格 (DEL) | ≠0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |