目录 搜索
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

允许直接在表达式中使用浮点类型的值。

句法

浮点常量是一个非左值表达式,其形式为:

significand exponent(optional) suffix(optional)



有效数字的形式。

whole-number(optional) .(optional) fraction(optional)



指数的形式。

e | E exponent-sign(optional) digit-sequence

(1)


p | P exponent-sign(optional) digit-sequence

(2)

(since C99)

1)十进制浮点常量的指数语法

2)十六进制浮点常量的指数语法

说明

如果有效数字以字符序列0x或0X开头,则浮点常量是一个十六进制浮点常量。否则,它是一个十进制浮点常量。对于十六进制浮点常量,有效数被解释为十六进制有理数,并且指数的数字序列被解释为必须缩放有效数的2的整数次幂。双d = 0x1.2p3; //十六进制小数1.2(十进制1.125)按2 ^ 3缩放,即9.0

(自C99以来)

对于十进制浮点常量,有效数被解释为十进制有理数,并且指数的数字序列被解释为10的整数幂,有效数必须被缩放到该幂。

double d = 1.2e3; // decimal fraction 1.2 scaled by 10^3, that is 1200.0

一个没有任何固定的浮点常量具有类型double。如果后缀是字母f或者F,浮动常数是类型的float。如果后缀是字母l或者L,浮动常数是类型的long double

评估浮点常量的结果或者是最接近的可表示值,或者是以实现定义的方式选择的紧邻最接近的可表示值的较大或较小的可表示值(换句话说,翻译期间的默认舍入方向是实现定义的) 。

如果由 FLT_EVAL_METHOD 指示,则浮点常量可能会转换为更多的范围和精度。例如,在表达式中,常数0.1f可能表现为0.1L。

(自C99以来)

如果 FLT_RADIX 为2,则评估十六进制浮点常量的结果是由浮点常量表示的精确值,正确地舍入到目标类型。

(自C99以来)

如果指数存在且不使用小数部分,则可以省略小数点分隔符:

double x = 1e0; // floating-point 1.0 (period not used)

对于十进制浮点常量,指数部分是可选的。如果省略,则该期间不是可选的,并且必须存在整数或分数。

double x = 1.; // floating-point 1.0 (fractional part optional)double y = .1; // floating-point 0.1 (whole-number part optional)

For hexadecimal floating constants, the exponent is not optional to avoid ambiguity resulting from an f suffix being mistaken as a hexadecimal digit.

(since C99)

对于十六进制浮点常量,指数不是可选的,以避免f后缀被误认为十六进制数字而引起的歧义。

(自C99以来)

当浮点常量转换为内部表示时,默认的舍入方向和精度有效,即使#pragma STDC FENV_ACCESS有效(对于字符串的执行时间转换,strtod也可以使用),浮点异常不会   产生。请注意,这与浮点类型的算术常量表达式不同。

在浮动常量字母是不区分大小写的:0x1.ep+30X1.EP+3表示相同的浮点值15.0。

指定的小数点setlocale对浮点常量的语法没有影响:小数点字符始终为句点。

与整数不同,并不是每个浮点值都可以用十进制或甚至十六进制常量语法直接表示:宏 NAN 和 INFINITY 以及诸如nan提供生成这些特殊值的方式的函数。请注意0x1.FFFFFEp128f,它可能看起来像一个 IEEE 浮点型NaN,实际上以这种格式溢出到无穷大。

没有负向浮动常量; 一个表达式,如-1.2算术运算符一元减号应用于浮点常量1.2。请注意,特殊值负零可以用-0.0

#include <stdio.h>
 int main(void){    printf("15.0     = %a\n", 15.0);    printf("0x1.ep+3 = %f\n", 0x1.ep+3); 
    // Constants outside the range of type double.    printf("+2.0e+308 --> %g\n",  2.0e+308);    printf("+1.0e-324 --> %g\n",  1.0e-324);    printf("-1.0e-324 --> %g\n", -1.0e-324);    printf("-2.0e+308 --> %g\n", -2.0e+308);}

输出:

15.0     = 0x1.ep+30x1.ep+3 = 15.000000+2.0e+308 --> inf+1.0e-324 --> 0-1.0e-324 --> -0-2.0e+308 --> -inf

参考

  • C11 standard (ISO/IEC 9899:2011):

    • 6.4.4.2 Floating constants (p: 65-66)

  • C99 standard (ISO/IEC 9899:1999):

    • 6.4.4.2 Floating constants (p: 57-58)

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

    • 3.1.3.1 Floating constants

上一篇: 下一篇: