试图打印 LDBL_MAX

问题描述

我将 CodeBlocks 20.03 与嵌入式 MinGW-W64 gcc 编译器版本 8.1.0 一起用于 Windows 10。 我正在尝试打印 LDBL_MIN 和 LDBL_MAX 常量，通常在 10e4932 的范围内，但我得到的值在 10e-317 的范围内。

这是我的代码：

#include <stdio.h>
#include <float.h>

main()
{
    printf("Unit \"long double\" -> %i bytes -> range %Lf - %Lf.\n",\
                        sizeof(long double),LDBL_MIN,LDBL_MAX);
    printf("Unit \"long double\" -> %i bytes -> range %Le - %Le.\n",LDBL_MAX);
    printf("Unit \"long double\" -> %i bytes -> range %Lg - %Lg.\n",LDBL_MAX);
    printf("Unit \"long double\" -> %i bytes -> range %LG - %LG.\n",LDBL_MAX);
}

结果：

Unit "long double" -> 16 bytes -> range 0.000000 - 0.000000.
Unit "long double" -> 16 bytes -> range 3.172905e-317 - 3.172897e-317.
Unit "long double" -> 16 bytes -> range 3.17291e-317 - 3.1729e-317.
Unit "long double" -> 16 bytes -> range 3.17291E-317 - 3.1729E-317.

知道为什么吗？

谢谢。

解决方法

如果您通过使用 /tmp/xander.c 编译 gcc -O -g /tmp/xander.c -o /tmp/xander -lm 来启用警告，您可以获得（在 Ubuntu 20 上，使用 GCC 9.3）

 pcbasile ~ 13:23 % gcc -O -g /tmp/xander.c -o /tmp/xander -lm
 /tmp/xander.c:4:1: warning: return type defaults to ‘int’ [-Wimplicit-int]
     4 | main()
       | ^~~~
 /tmp/xander.c: In function ‘main’:
 /tmp/xander.c:6:38: warning: format ‘%i’ expects argument of type ‘int’,but argument 2 has type ‘long unsigned int’ [-Wformat=]
     6 |     printf("Unit \"long double\" -> %i bytes -> range %Lf - %Lf.\n",\
       |                                     ~^
       |                                      |
       |                                      int
       |                                     %li
     7 |                         sizeof(long double),LDBL_MIN,LDBL_MAX);
       |                         ~~~~~~~~~~~~~~~~~~~
       |                         |
       |                         long unsigned int
 /tmp/xander.c:8:38: warning: format ‘%i’ expects argument of type ‘int’,but argument 2 has type ‘long unsigned int’ [-Wformat=]
     8 |     printf("Unit \"long double\" -> %i bytes -> range %Le - %Le.\n",\
       |                                     ~^
       |                                      |
       |                                      int
       |                                     %li
     9 |                         sizeof(long double),LDBL_MAX);
       |                         ~~~~~~~~~~~~~~~~~~~
       |                         |
       |                         long unsigned int
 /tmp/xander.c:10:38: warning: format ‘%i’ expects argument of type ‘int’,but argument 2 has type ‘long unsigned int’ [-Wformat=]
    10 |     printf("Unit \"long double\" -> %i bytes -> range %Lg - %Lg.\n",\
       |                                     ~^
       |                                      |
       |                                      int
       |                                     %li
    11 |                         sizeof(long double),LDBL_MAX);
       |                         ~~~~~~~~~~~~~~~~~~~
       |                         |
       |                         long unsigned int
 /tmp/xander.c:12:38: warning: format ‘%i’ expects argument of type ‘int’,but argument 2 has type ‘long unsigned int’ [-Wformat=]
    12 |     printf("Unit \"long double\" -> %i bytes -> range %LG - %LG.\n",\
       |                                     ~^
       |                                      |
       |                                      int
       |                                     %li
    13 |                         sizeof(long double),LDBL_MAX);
       |                         ~~~~~~~~~~~~~~~~~~~
       |                         |
       |                         long unsigned int
 pcbasile ~ 13:24 % gcc -O -g /tmp/xander.c -o /tmp/xander

所以你的格式 %i 是错误的；将 %i 替换为 %zi 后，输出在运行时看起来会更好：

Unit "long double" -> 16 bytes -> range 0.000000 - 1189731495357231765021263853030970205169063322294624200440323733891737005522970722616410290336528882853545697807495577314427443153670288434198125573853743678673593200706973263201915918282961524365529510646791086614311790632169778838896134786560600399148753433211454911160088679845154866512852340149773037600009125479393966223151383622417838542743917838138717805889487540575168226347659235576974805113725649020884855222494791399377585026011773549180099796226026859508558883608159846900235645132346594476384939859276456284579661772930407806609229102715046085388087959327781622986827547830768080040150694942303411728957777100335714010559775242124057347007386251660110828379119623008469277200965153500208474470792443848545912886723000619085126472111951361467527633519562927597957250278002980795904193139603021470997035276467445530922022679656280991498232083329641241038509239184734786121921697210543484287048353408113042573002216421348917347174234800714880751002064390517234247656004721768096486107994943415703476320643558624207443504424380566136017608837478165389027809576975977286860071487028287955567141404632615832623602762896316173978484254486860609948270867968048078702511858930838546584223040908805996294594586201903766048446790926002225410530775901065760671347200125846406957030257138960983757998926954553052368560758683179223113639519468850880771872104705203957587480013143131444254943919940175753169339392366881856189129931729104252921236835159922322050998001677102784035360140829296398115122877768135706045789343535451696539561254048846447169786893211671087229088082778350518228857646062218739702851655083720992349483334435228984751232753726636066213902281264706234075352071724058665079518217303463782631353393706774901950197841690441824738063162828586857741432581165364040218402724913393320949219498422442730427019873044536620350262386957804682003601447291997123095530057206141866974852846856186514832715974481203121946751686379343096189615107330065552421485195201762858595091051839472502863871632494167613804996319791441870254302706758495192008837915169401581740046711477877201459644461175204059453504764721807975761111720846273639279600339670470037613374509553184150073796412605047923251661354841291884211340823015473304754067072818763503617332908005951896325207071673904547777129682265206225651439919376804400292380903112437912614776255964694221981375146967079446870358004392507659451618379811859392049544036114915310782251072691486979809240946772142727012404377187409216756613634938900451232351668146089322400697993176017805338191849981933008410985993938760292601390911414526003720284872132411955424282101831204216104467404621635336900583664606591156298764745525068145003932941404131495400677602951005962253022823003631473824681059648442441324864573137437595096416168048024129351876204668135636877532814675538798871771836512893947195335061885003267607354388673368002074387849657014576090349857571243045102038730494854256702479339322809110526041538528994849203991091946129912491633289917998094380337879522093131466946149705939664152375949285890960489916121944989986384837022486672249148924678410206183364627416969576307632480235587975245253737035433882960862753427740016333434055083537048507374544819754722228975281083020898682633020285259923084168054539687911418297629988964576482765287504562854924265165217750799516259669229114977788962356670956627138482018191348321687995863652637620978285070099337294396784639879024914514222742527006363942327998483976739987154418554201562244154926653014515504685489258620276085761837129763358761215382565129633538141663949516556000264159186554850057052611431952919918807954522394649627635630178580896692226406235382898535867595990647008385687123810329591926494846250768992258419305480763620215089022149220528069842018350840586938493815498909445461977893029113576516775406232278298314033473276603952231603422824717528181818844304880921321933550869873395861276073670866652375555675803171490108477320096424318780070008797346032906278943553743564448851907191616455141155761939399690767415156402826543664026760095087523945507341556135867933066031744720924446513532366647649735400851967040771103640538150073486891798364049570606189535005089840913826869535090066783324472578712196604415284924840041850932811908963634175739897166596000759487800619164094854338758520657116541072260996288150123144377944008749301944744330784388995701842710004808305012177123560622895076269042856800047718893158089358515593863176652948089031267747029662545110861548958395087796755464137944895960527975209874813839762578592105756284401759349324162148339565350189196811389091843795734703269406342890087805846940352453479398080674273236297887100867175802531561302356064878709259865288416350972529537091114317204887747405539054009425375424119317944175137064689643861517718849867010341532542385911089624710885385808688837777258648564145934262121086647588489260031762345960769508849149662444156604419552086811989770240.000000.
Unit "long double" -> 16 bytes -> range 3.362103e-4932 - 1.189731e+4932.
Unit "long double" -> 16 bytes -> range 3.3621e-4932 - 1.18973e+4932.
Unit "long double" -> 16 bytes -> range 3.3621E-4932 - 1.18973E+4932.

记住 sizeof(int) 是 4，但 sizeof(sizeof(long double)) 就像 sizeof(long) 8 个字节