C语言条件编译详解

时间：2015-04-27 13:06:12 阅读：135 评论：0 收藏：0 [点我收藏+]

标签：

预处理程序提供了条件编译的功能。可以按不同的条件去编译不同的程序部分，因而产生不同的目标代码文件。这对于程序的移植和调试是很有用的。条件编译有三种形式，下面分别介绍。

第一种形式

第一种形式的格式为：
#ifdef 标识符
程序段1
#else
程序段2
#endif

它的功能是，如果标识符已被 #define命令定义过则对程序段1进行编译；否则对程序段2进行编译。如果没有程序段2（它为空），本格式中的#else可以没有，即可以写为：
#ifdef 标识符
程序段
#endif

【例9-12】

#include <stdio.h>
#define NUM ok
int main(void){
struct stu{
int num;
char *name;
char sex;
float score;
} *ps;
ps=(struct stu*)malloc(sizeof(struct stu));
ps->num=102;
ps->name="Zhang ping";
ps->sex=‘M‘;
ps->score=62.5;
#ifdef NUM
printf("Number=%d\nScore=%f\n",ps->num,ps->score);
#else
printf("Name=%s\nSex=%c\n",ps->name,ps->sex);
#endif
free(ps);
return 0;
}

由于在程序的第14行插入了条件编译预处理命令，因此要根据NUM是否被定义过来决定编译那一个printf语句。而在程序的第一行已对NUM作过宏定义，因此应对第一个printf语句作编译故运行结果是输出了学号和成绩。

在程序的第1行宏定义中，定义NUM表示字符串OK，其实也可以为任何字符串，甚至不给出任何字符串，写为：

#define NUM

也具有同样的意义。只有取消程序的第1行才会去编译第二个printf语句。读者可上机试作。

第二种形式

第二种形式的格式为：
#ifndef 标识符
程序段1
#else
程序段2
#endif
与第一种形式的区别是将“ifdef”改为“ifndef”。它的功能是，如果标识符未被#define命令定义过则对程序段1进行编译，否则对程序段2进行编译。这与第一种形式的功能正相反。

http://www.zbnews.net/jiankang/list1/234895.html
http://www.zbnews.net/jiankang/list1/234894.html
http://www.zbnews.net/jiankang/list1/234891.html
http://www.51etong.com/jkzt/list1/234889.html
http://www.zbnews.net/jiankang/list1/234887.html
http://www.51etong.com/jkzt/list1/234886.html
http://www.zbnews.net/jiankang/list1/234885.html
http://www.zbnews.net/jiankang/list1/234884.html
http://www.zbnews.net/jiankang/list1/234882.html
http://www.51etong.com/jkzt/list1/234880.html
http://www.lznews.gov.cn/uzt/list1/234879.html
http://www.lznews.gov.cn/uzt/list1/234878.html
http://www.51etong.com/jkzt/list1/234876.html
http://www.lznews.gov.cn/uzt/list1/234875.html
http://www.lznews.gov.cn/uzt/list1/234874.html
http://www.lznews.gov.cn/uzt/list1/234873.html
http://www.zbnews.net/jiankang/list1/234872.html
http://www.51etong.com/jkzt/list1/234871.html
http://www.51etong.com/jkzt/list1/234870.html
http://www.51etong.com/jkzt/list1/234867.html
http://user.qzone.qq.com/2633883405
http://t.qq.com/changchuny8250
http://health.people.com.cn/xywy/wfyxb/tp/8634716732.html
http://health.people.com.cn/xywy/wfyxb/tp/8634711498.html
http://health.people.com.cn/xywy/wfyxb/tp/8634708130.html
http://health.people.com.cn/xywy/wfyxb/tp/8634705327.html
http://health.people.com.cn/xywy/wfyxb/tp/8634702557.html
http://health.people.com.cn/xywy/wfyxb/tp/8634699443.html
http://health.people.com.cn/xywy/wfyxb/tp/8634695041.html
http://health.people.com.cn/xywy/wfyxb/tp/8634692366.html
http://health.people.com.cn/xywy/wfyxb/tp/8634689457.html
http://health.people.com.cn/xywy/wfyxb/tp/8634686655.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8634680004.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8634675843.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8634671613.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8634668953.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8634665768.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8634662151.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8634659390.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8634655387.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8634652223.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8634648791.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8634645687.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8634642791.html
http://health.people.com.cn/xywy/wfyxb/zl/8634639673.html
http://health.people.com.cn/xywy/wfyxb/zl/8634636341.html
http://health.people.com.cn/xywy/wfyxb/zl/8634633176.html
http://health.people.com.cn/xywy/wfyxb/zl/8634629876.html
http://health.people.com.cn/xywy/wfyxb/zl/8634626116.html
http://health.people.com.cn/xywy/wfyxb/zl/8634621396.html
http://health.people.com.cn/xywy/wfyxb/zl/8634618202.html
http://health.people.com.cn/xywy/wfyxb/zl/8634615071.html
http://health.people.com.cn/xywy/wfyxb/zl/8634612138.html
http://health.people.com.cn/xywy/wfyxb/kfal/8634608141.html
http://health.people.com.cn/xywy/wfyxb/kfal/8634601130.html
http://health.people.com.cn/xywy/wfyxb/kfal/8634598198.html
http://health.people.com.cn/xywy/wfyxb/kfal/8634595171.html
http://health.people.com.cn/xywy/wfyxb/kfal/8634591848.html
http://health.people.com.cn/xywy/wfyxb/kfal/8634587855.html
http://health.people.com.cn/xywy/wfyxb/kfal/8634584673.html
http://health.people.com.cn/xywy/wfyxb/kfal/8634580296.html
http://health.people.com.cn/xywy/wfyxb/kfal/8634576927.html
http://health.people.com.cn/xywy/wfyxb/kfal/8634572513.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8634568629.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8634565548.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8634561012.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8634558160.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8634555287.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8634551027.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8634546991.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8634543966.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8634540202.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8665825627.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8665803242.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8665760857.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8665738541.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8665725796.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8665705278.html
http://health.people.com.cn/xywy/wfyxb/npxpf/8665676307.html
http://health.people.com.cn/xywy/wfyxb/tp/8665652613.html
http://health.people.com.cn/xywy/wfyxb/tp/8665634968.html
http://health.people.com.cn/xywy/wfyxb/tp/8665618204.html
http://health.people.com.cn/xywy/wfyxb/tp/8665599559.html
http://health.people.com.cn/xywy/wfyxb/tp/8665570637.html
http://health.people.com.cn/xywy/wfyxb/tp/8665546616.html
http://health.people.com.cn/xywy/wfyxb/tp/8665516148.html
http://health.people.com.cn/xywy/wfyxb/tp/8665494052.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8665348011.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8665332141.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8665304778.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8665279337.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8665245471.html
http://health.people.com.cn/xywy/wfyxb/wfyxb/8665217641.html
http://health.people.com.cn/xywy/wfyxb/zl/8665183707.html
http://health.people.com.cn/xywy/wfyxb/zl/8665151882.html
http://health.people.com.cn/xywy/wfyxb/zl/8665126913.html
http://health.people.com.cn/xywy/wfyxb/zl/8665095276.html
http://health.people.com.cn/xywy/wfyxb/zl/8665065223.html
http://health.people.com.cn/xywy/wfyxb/zl/8665044459.html
http://health.people.com.cn/xywy/wfyxb/zl/8665016966.html
http://health.people.com.cn/xywy/wfyxb/zl/8664994329.html
http://health.people.com.cn/xywy/wfyxb/zl/8664964107.html
http://health.people.com.cn/xywy/wfyxb/zl/8664946776.html
http://health.people.com.cn/xywy/wfyxb/kfal/8664904496.html
http://health.people.com.cn/xywy/wfyxb/kfal/8664875723.html
http://health.people.com.cn/xywy/wfyxb/kfal/8664841175.html
http://health.people.com.cn/xywy/wfyxb/kfal/8664820153.html
http://health.people.com.cn/xywy/wfyxb/kfal/8664800127.html
http://health.people.com.cn/xywy/wfyxb/kfal/8664786867.html
http://health.people.com.cn/xywy/wfyxb/kfal/8664757276.html
http://health.people.com.cn/xywy/wfyxb/kfal/8664738646.html
http://health.people.com.cn/xywy/wfyxb/kfal/8664718323.html
http://health.people.com.cn/xywy/wfyxb/kfal/8664688557.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8664668308.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8664646362.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8664631785.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8664603483.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8664580771.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8664560208.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8664545675.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8664532567.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8664505390.html
http://health.people.com.cn/xywy/wfyxb/yyxw/8664484808.html

第三种形式

第三种形式的格式为：
#if 常量表达式
程序段1
#else
程序段2
#endif
它的功能是，如常量表达式的值为真（非0），则对程序段1 进行编译，否则对程序段2进行编译。因此可以使程序在不同条件下，完成不同的功能。

【例9-13】

#include <stdio.h>
#define R 1
int main(void){
float c,r,s;
printf ("input a number: ");
scanf("%f",&c);
#if R
r=3.14159*c*c;
printf("area of round is: %f\n",r);
#else
s=c*c;
printf("area of square is: %f\n",s);
#endif
return 0;
}

本例中采用了第三种形式的条件编译。在程序第1行宏定义中，定义R为1，因此在条件编译时，常量表达式的值为真，故计算并输出圆面积。

C语言条件编译详解

标签：

原文地址：http://www.cnblogs.com/guguniao/p/4459684.html

踩

(0)

评论一句话评论（0）

分享档案

更多>

2021年07月29日 (22)
2021年07月28日 (40)
2021年07月27日 (32)
2021年07月26日 (79)
2021年07月23日 (29)
2021年07月22日 (30)
2021年07月21日 (42)
2021年07月20日 (16)
2021年07月19日 (90)
2021年07月16日 (35)

周排行