C语言中条件编译语句的类别、格式及应用场景全解析

在C语言中支持的条件编译语句主要包含以下几类。若要论条件编译#if...#else 与分支语句 if...else 的最大差别其中一点就是条件编译针对那些不满足要求的代码是会在编译期予以处理的并且不会被包含在最终执行的程序当中而分支语句则会涵盖所有的运行逻辑。然而这也对条件编译的变量提出了要求那就是该变量必须在编译期就得以确定不能够在运行时进行动态的改变。条件编译#ifdef对于条件编译#ifdef它主要是用来判定参数是不是被定义了要是被定义了那就去执行相应代码块分支要是没被定义那就执行其他分支或者是不予以支持。对于#ifdef语句其格式如下所示。// #ifdef定义判断 #ifdef [var] // body #else // body #endif // 举例说明 #ifdef DEBUG printf(debug mode\n); #endififdef语句常常被运用在C/C混合编程里用来判定是不是C编译环境具体的示例像下面所展示的这样。// 支持C/C混合编程 #ifdef __cplusplus extern C { #endif //... #ifdef __cplusplus } #endif条件编译#ifndef对于条件编译里面的#ifndef语句而言其主要是用来判定参数是不是未被定义当未被定义的时候就会被包含于代码当中而当被定义的时候则会包含其他分支或者不包含其他代码。#ifndef语句其格式如下所示。// #ifndef未定义判断 #ifndef [var] // body #else // body #endif // 举例说明 #ifndef DEBUG printf(release mode\n); #endififndef语句常被用于头文件里用来防止重复包含具体的示例如下所展示的那样。// 头文件避免重复包含 #ifndef _INC_DRIVER_H #define _INC_DRIVER_H // ... #endif条件编译#if存在一种条件语句名为#if其主要作用在于展开条件判断工作那些符合条件的代码会被收纳于代码范围之内反之若是不符合条件则不会被收纳。#if语句其格式如下所示。// #if条件编译格式 #if [表达式] // body #elif [表达式] // body #else // body #endif // 举例说明 #define MODE_RUN 0 #define MODE_DEBUG 1 #define MODE_TEST 2 #define RUN_MODE MODE_DEBUG #if RUN_MODE MODE_RUN printf(run mode\n); #elif RUN_MODE MODE_DEBUG printf(debug mode\n); #elif RUN_MODE MODE_TEST printf(test mode\n); #else #error invalid mode, need choose one mode #endif关于#if语句它的运用方式跟if语句相像同样支持平常的表达式、比较运算符以及逻辑运算符、||、!等等用以判定条件是不是成立具体的示例如下所展示的那样。#define NUMS 100 // 判断NUMS是否在10到100之间是则执行 #if ((NUMS 10) (NUMS 100)) printf(NUMS is between 10 and 100\n); #endif // 判断NUMS是否大于等于1000或者小于0是则执行 #if ((NUMS 1000) || (NUMS 0)) printf(NUMS is out of range!\n); #endif当然对于#if而言存在着另外一种扩展功能此功能是对#if define(def)这种格式予以支持从而达成类似于#ifdef的功能其作用在于判定参数有没有被定义要是被定义了那么就将执行代码块涵盖进来反之要是没有被定义那么就不会被囊括在代码之中。// #if配合defined的定义 #if defined(var) // body #elif defined(var_1) // body #else // body #endif // 举例说明 #if defined(DEBUG) printf(debug mode); #endif能够瞧见如同#ifdef那般#if同样能够用以判定参数是不是被定义然而相较于仅仅查看定义而言它还支持借助表达式处理判断从而开展分支的选择编译针对于不被支持的参数会径直忽略不会参与到代码的生成里面。当然咯运用if语句通常会与#define配合使用也能够选择执行不同的代码块不过相较于#if所需的代码量更多并且在执行的时候需要依据分支来执行效率没有#if那么高。另外于使用#if之际运用表达式之时建议依旧采用括号进行包裹以防因优先级问题而引发出错误。灵活运用#if、#ifdef、#ifndef等语句以满足不同平台之下的需求。lo.honorcent.comlp.honorcent.comlq.honorcent.comlr.honorcent.comls.honorcent.comlt.honorcent.comlu.honorcent.comlv.honorcent.comlw.honorcent.comlx.honorcent.comly.honorcent.comlz.honorcent.comma.honorcent.commb.honorcent.commc.honorcent.commd.honorcent.comme.honorcent.commf.honorcent.commg.honorcent.commh.honorcent.commi.honorcent.commj.honorcent.commk.honorcent.comml.honorcent.commm.honorcent.commn.honorcent.commo.honorcent.commp.honorcent.commq.honorcent.commr.honorcent.comms.honorcent.commt.honorcent.commu.honorcent.commv.honorcent.commw.honorcent.commx.honorcent.commy.honorcent.commz.honorcent.comna.honorcent.comnb.honorcent.comnc.honorcent.comnd.honorcent.comne.honorcent.comnf.honorcent.comng.honorcent.comnh.honorcent.comni.honorcent.comnj.honorcent.comnk.honorcent.comnl.honorcent.comnm.honorcent.comnn.honorcent.comno.honorcent.comnp.honorcent.comnq.honorcent.comnr.honorcent.comns.honorcent.comnt.honorcent.comnu.honorcent.comnv.honorcent.comnw.honorcent.comnx.honorcent.comny.honorcent.comnz.honorcent.comoa.honorcent.comob.honorcent.comoc.honorcent.comod.honorcent.comoe.honorcent.comof.honorcent.comog.honorcent.comoh.honorcent.comoi.honorcent.comoj.honorcent.comok.honorcent.comol.honorcent.comom.honorcent.comon.honorcent.comoo.honorcent.comop.honorcent.comoq.honorcent.comor.honorcent.comos.honorcent.comot.honorcent.comou.honorcent.comov.honorcent.comow.honorcent.comox.honorcent.comoy.honorcent.comoz.honorcent.compa.honorcent.compb.honorcent.compc.honorcent.compd.honorcent.compe.honorcent.compf.honorcent.compg.honorcent.comph.honorcent.compi.honorcent.compj.honorcent.compk.honorcent.compl.honorcent.compm.honorcent.compn.honorcent.compo.honorcent.compp.honorcent.compq.honorcent.compr.honorcent.comps.honorcent.compt.honorcent.compu.honorcent.compv.honorcent.compw.honorcent.compx.honorcent.compy.honorcent.compz.honorcent.comqa.honorcent.comqb.honorcent.comqc.honorcent.comqd.honorcent.comqe.honorcent.comqf.honorcent.comqg.honorcent.comqh.honorcent.comqi.honorcent.comqj.honorcent.comqk.honorcent.comql.honorcent.comqm.honorcent.comqn.honorcent.comqo.honorcent.comqp.honorcent.comqq.honorcent.comqr.honorcent.comqs.honorcent.comqt.honorcent.comqu.honorcent.comqv.honorcent.comqw.honorcent.comqx.honorcent.comqy.honorcent.comqz.honorcent.comra.honorcent.comrb.honorcent.comrc.honorcent.comrd.honorcent.comre.honorcent.comrf.honorcent.comrg.honorcent.comrh.honorcent.comri.honorcent.comrj.honorcent.comrk.honorcent.comrl.honorcent.comrm.honorcent.comrn.honorcent.comro.honorcent.comrp.honorcent.comrq.honorcent.comrr.honorcent.comrs.honorcent.comrt.honorcent.comru.honorcent.comrv.honorcent.comrw.honorcent.comrx.honorcent.comry.honorcent.comrz.honorcent.comsa.honorcent.comsb.honorcent.comsc.honorcent.comsd.honorcent.comse.honorcent.comsf.honorcent.comsg.honorcent.comsh.honorcent.comsi.honorcent.comsj.honorcent.comsk.honorcent.comsl.honorcent.comsm.honorcent.comsn.honorcent.comso.honorcent.comsp.honorcent.comsq.honorcent.comsr.honorcent.comss.honorcent.comst.honorcent.comsu.honorcent.comsv.honorcent.comsw.honorcent.comsx.honorcent.comsy.honorcent.comsz.honorcent.comta.honorcent.comtb.honorcent.comtc.honorcent.comtd.honorcent.comte.honorcent.comtf.honorcent.comtg.honorcent.comth.honorcent.comti.honorcent.comtj.honorcent.comtk.honorcent.comtl.honorcent.comtm.honorcent.comtn.honorcent.comto.honorcent.comtp.honorcent.comtq.honorcent.comtr.honorcent.comts.honorcent.comtt.honorcent.comtu.honorcent.comtv.honorcent.comtw.honorcent.comtx.honorcent.comty.honorcent.comtz.honorcent.comua.honorcent.comub.honorcent.comuc.honorcent.comud.honorcent.comue.honorcent.comuf.honorcent.comug.honorcent.comuh.honorcent.comui.honorcent.comuj.honorcent.comuk.honorcent.comul.honorcent.comum.honorcent.comun.honorcent.comuo.honorcent.comup.honorcent.comuq.honorcent.comur.honorcent.comus.honorcent.comut.honorcent.comuu.honorcent.comuv.honorcent.comuw.honorcent.comux.honorcent.comuy.honorcent.comuz.honorcent.comva.honorcent.comvb.honorcent.comvc.honorcent.comvd.honorcent.comve.honorcent.comvf.honorcent.comvg.honorcent.comvh.honorcent.comvi.honorcent.comvj.honorcent.comvk.honorcent.comvl.honorcent.comvm.honorcent.comvn.honorcent.comvo.honorcent.comvp.honorcent.comvq.honorcent.comvr.honorcent.comvs.honorcent.comvt.honorcent.comvu.honorcent.comvv.honorcent.comvw.honorcent.comvx.honorcent.comvy.honorcent.comvz.honorcent.comwa.honorcent.comwb.honorcent.comwc.honorcent.comwd.honorcent.comwe.honorcent.comwf.honorcent.comwg.honorcent.comwh.honorcent.comwi.honorcent.comwj.honorcent.comwk.honorcent.comwl.honorcent.comwm.honorcent.comwn.honorcent.comwo.honorcent.comwp.honorcent.comwq.honorcent.comwr.honorcent.comws.honorcent.comwt.honorcent.comwu.honorcent.comwv.honorcent.comww.honorcent.comwx.honorcent.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