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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) 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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
문자

允许直接在表达式中使用整数类型的值。

句法

整型常量是表单的非左值表达式。

decimal-constant integer-suffix(optional)

(1)


octal-constant integer-suffix(optional)

(2)


hex-constant integer-suffix(optional)

(3)


其中

  • 十进制常数是一个非零十进制数(123456789),随后的零个或多个十进制数字(0123456789

  • 八进制常数是数字零(0),接着是零个或更多八进制数字(01234567

  • 十六进制常数是字符序列0x或字符序列0X后跟一个或多个十六进制数字(0123456789aAbBcCdDeEfF

  • 整数后缀(如果提供)可能包含以下一项或两项(如果同时提供了这两项),它们可能以任何顺序出现:

    • 无符号后缀(字符u或字符U

    • 长后缀(字符l或字符L)或长后缀(字符序列ll或字符序列LL)(自C99以来)

说明

1)十进制整数常量(以10为底,第一位数字最重要)。

2)八进制整数常量(基数8,第一位数字最重要)。

3)十六进制整数常量(基数16,第一个数字是最重要的,字母'a'到'f'代表十进制值10到15)。

以下变量初始化为相同的值:

int d = 42;int o = 052;int x = 0x2a;int X = 0X2A;

整型常量的类型

整数常量的类型是该值可以匹配的第一个类型,它取决于使用哪个数字库和哪个整数后缀的类型列表。

| 整数常量允许的类型|

|:----|

| suffix | decimal bases | hexadecimal or octal bases |

| no suffix | int long int unsigned long int (until C99) long long int (since C99). | int unsigned int long int unsigned long int long long int(since C99) unsigned long long int(since C99). |

| u or U | unsigned int unsigned long int unsigned long long int(since C99). | unsigned int unsigned long int unsigned long long int(since C99). |

| l or L | long int unsigned long int(until C99) long long int(since C99). | long int unsigned long int long long int(since C99) unsigned long long int(since C99). |

| both l/L and u/U | unsigned long int unsigned long long int(since C99). | unsigned long int unsigned long long int(since C99). |

| ll or LL | long long int(since C99) | long long int(since C99) unsigned long long int(since C99). |

| both ll/LL and u/U | unsigned long long int(since C99) | unsigned long long int(since C99) |

如果整数常量的值太大而不适合后缀/基数组合所允许的任何类型,并且编译器支持扩展整数类型(如__int128),则该常量可以是扩展整数类型; 否则,该计划是不合格的。

笔记

在整数常量字母是不区分大小写的:0xDeAdBaBeU0XdeadBABEu表示相同的数目(一个例外是长长后缀,其是llLL,从未lLLl)。

没有负整数常量。诸如-1将一元减号运算符应用于由常量表示的值的表达式可能涉及隐式类型转换。

当在#if或#elif的控制表达式中使用时,所有有符号整型常量的作用就好像它们具有类型,intmax_t并且所有无符号整型常数的作用就好像它们具有类型一样uintmax_t

整型常量可以用在整型常量表达式中。

#include <stdio.h>
 int main(void){    printf("123 = %d\n", 123);    printf("0123 = %d\n", 0123);    printf("0x123 = %d\n", 0x123);    printf("12345678901234567890ull = %llu\n", 12345678901234567890ull);    // the type is unsigned long long even without a long long suffix    printf("12345678901234567890u = %llu\n", 12345678901234567890u ); //  printf("%lld\n", -9223372036854775808); // ERROR// the value 9223372036854775808 cannot fit in signed long long, which is the// biggest type allowed for unsuffixed decimal integer constant 
    printf("%llu\n", -9223372036854775808u );    // unary minus applied to unsigned value subtracts it from 2^64,    // this gives 9223372036854775808 
    printf("%lld\n", -9223372036854775807 - 1);    // // correct way to represent the value -9223372036854775808}

输出:

123 = 1230123 = 830x123 = 29112345678901234567890ull = 1234567890123456789012345678901234567890u = 123456789012345678909223372036854775808-9223372036854775808

参考

  • C11 standard (ISO/IEC 9899:2011):

    • 6.4.4.1 Integer constants (p: 62-64)

  • C99 standard (ISO/IEC 9899:1999):

    • 6.4.4.1 Integer constants (p: 54-56)

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

    • 3.1.3.2 Integer constants

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