C语言进阶课程学习记录-第22课 - 条件编译使用分析

- 条件编译基本概念
- 条件编译实验
- 条件编译本质
- 实验-ifdef
- include本质
- 实验-间接包含同一个头文件
- 解决重复包含的方法-ifndef
- 实验-条件编译的应用
- 小结

本文学习自狄泰软件学院唐佐林老师的 C语言进阶课程，图片全部来源于课程PPT，仅用于个人学习记录

条件编译基本概念

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条件编译实验

#include <stdio.h>#define C 1int main()
{const char* s;#if( C == 1 )s = "This is first printf...\n";#elses = "This is second printf...\n";#endifprintf("%s", s);return 0;
}/*output:
This is first printf...*/

条件编译本质

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实验-ifdef

#include <stdio.h>int main()
{const char* s;#ifdef Cs = "This is first printf...\n";#elses = "This is second printf...\n";#endifprintf("%s", s);return 0;
}/*output:
This is second printf...*/

include本质

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实验-间接包含同一个头文件

// global.h
//#ifndef _GLOBAL_H_
//#define _GLOBAL_H_
int global = 10;//D:\Users\cy\Test\global.h|4|error: redefinition of 'global'|//#endif// test.h//#ifndef _TEST_H_
//#define _TEST_H_
#include "global.h"
const char* NAME = "test.h";
char* hello_world(){    return "Hello world!\n";}//#endif#include <stdio.h>
#include "test.h"
#include "global.h"int main()
{const char* s = hello_world();int g = global;printf("%s\n", NAME);printf("%d\n", g);return 0;
}//error  D:\Users\cy\Test\global.h|4|error: redefinition of 'global'|

// global.h
#ifndef _GLOBAL_H_
#define _GLOBAL_H_
int global = 10;
#endif// test.h#ifndef _TEST_H_
#define _TEST_H_
#include "global.h"
const char* NAME = "test.h";
char* hello_world(){    return "Hello world!\n";}#endif#include <stdio.h>
#include "test.h"
#include "global.h"int main()
{const char* s = hello_world();int g = global;printf("%s\n", NAME);printf("%d\n", g);return 0;
}/*output:
test.h
10*/

解决重复包含的方法-ifndef

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实验-条件编译的应用

“product.h”

#define DEBUG 1
#define HIGH  1

#include <stdio.h>
#include "product.h"#if DEBUG#define LOG(s) printf("[%s:%d] %s\n", __FILE__, __LINE__, s)
#else#define LOG(s) NULL
#endif#if HIGH
void f()
{printf("This is the high level product!\n");
}
#else
void f()
{
}
#endifint main()
{LOG("Enter main() ...");f();printf("1. Query Information.\n");printf("2. Record Information.\n");printf("3. Delete Information.\n");#if HIGHprintf("4. High Level Query.\n");printf("5. Mannul Service.\n");printf("6. Exit.\n");#elseprintf("4. Exit.\n");#endifLOG("Exit main() ...");return 0;
}/*output:
[D:\Users\cy\Test\test1.c:143] Enter main() ...
This is the high level product!
1. Query Information.
2. Record Information.
3. Delete Information.
4. High Level Query.
5. Mannul Service.
6. Exit.
[D:\Users\cy\Test\test1.c:159] Exit main() ...*/