[C] Preprocessing Commands - 1

Because I need to use C language programming in my work and study, I often encounter[^1] the situation[^2] that I have a little understanding of some grammar. So I have the idea of studying C language syntax[^3] from the beginning. This chapter[^4] will study the preprocessing command part of the C language. Starting from the meaning of the command, the use of examples to complete the whole process[^5] of learning.

environment[^7]

• Windows 11 Pro Version: 22H2.
• Visual Studio Code Version: 1.74.2 with C/C++ extensions[^8].

Let’s write a basic c program:

1
2
3
4
5
6
7

#include <stdio.h>

int main()
{
    printf("Hello, World! \n");
    return 0;
}

The output from this program is:

1

Hello, World!

Insert[^9],contents[^10]

First let’s look at the meaning of the first line, This line of code has two parts: #include and <stdio.h>.
This command takes two forms:

1
2

#include <filename>
#include "filename"

Using <> Is searched[^11] for filename in the system standard library

Using “” means searching for filename in the current directory

#include is one of several C preprocessing commands. Preprocess commands are commands that are used before the program is executed.

All preprocessing commands in C are as follows:

• #define
• #include
• #,##
• #error
• #if, #ifdef, #ifndef, #else, #elif, #endif
• #line
• #pragma
• #undef

Syntax:

The #define command is used to replace[^13] the replacement-string with macro-name . In other words, #define causes the compiler to define each of the replacement-string with a new macro-name . The substituted[^14] string terminates[^15] at the end of the line.

For example:

1
2

#define TRUE 1
#define FALSE 0

These two statements mean give 1 a new name： TRUE ; and give 0 a new name： FALSE .

Later in the program, you can just use TRUE and FALSE instead of 1 and 0 .

Another thing the #define command does is replace, make it look like have created a function.

For example:

1

#define Compare_sizes(a,b) a>b

It does the same thing as defining a subfunction:

1
2
3
4
5
6

int Compare_sizes (int a, int b)
{
    int result = 0;
    result = a > b;
    return result;
}

It is used in the same way:

1
2
3
4

//#define
c = Compare_sizes(a,b);
//defining a subfunction
c = Compare_sizes(a,b);

These two statements mean that a is compared to b, which outputs TRUE if a is greater[^16] than b and FALSE if a is less than b.

[^1]: encounter /ɪnˈkaʊntə®/
v. 遭遇；偶遇，邂逅
n. 偶遇，邂逅；经历，体验；冲突；比赛，交锋

[^2]: situation /ˌsɪtʃuˈeɪʃ(ə)n/
n. 情况，形势；重要问题，突发情况；（建筑物或城镇的）地理位置，环境特点；<旧，正式>工作，职位

[^3]: syntax /ˈsɪntæks/
n. 句法，句法规则；（计算机语言的）句法，语构；句子结构分析法；句法学

[^4]: chapter /ˈtʃæptə®/
n. 章，回，篇；阶段，时期；分会，分部；议会法案；一系列，一连串（a chapter of）；全体教士；宗教团体理事会
v. 把……分成章节

[^5]: process /ˈprəʊses/
n. 步骤，程序；（自然或偶然的）变化过程；（为达到某目标的）过程，进程；制作方法，加工方法；<法律>传票；（生，剖）端突，突起
adj. （印刷）三原色的，三色版的； 经过特殊加工的；照相板的
v. （用化学物品或机器）处理，加工；审核，受理（正式文件或请求）；（计算机）处理（数据）；冲洗（照片）；加工（食品）；<正式>列队行进；把（头发）弄成直发

[^6]: contributing /ˈkɒntrɪbjuːtɪŋ/
adj. 贡献的；起作用的
v. 捐献（contribute 的 ing 形式）

[^7]: environment /ɪnˈvaɪrənmənt/
n. 自然环境，生态环境；周围状况，条件；工作平台，软件包

[^8]: extension /ɪkˈstenʃ(ə)n/
n. 延伸，扩展；展期，延长期；扩建部分，延伸部分；（电话）分机；扩展名；（为非全日制学生开设的）进修部；牵伸（术）；外延；广延（性）

[^9]: Insert /ɪnˈsɜːt/
v. 插入，嵌入；（在文章中）添加，加插；使参与（活动）；（肌肉或其他器官）附着于（尤指移动部分）
n. 插入物；（尤指）插页，附加页；（电影等的）插入镜头

[^10]: contents /ˈkɒntents/
n. 内容；[图情] [计] 目录；要旨（content 的复数）
v. 使满意（content 的三单形式）

[^11]: search /sɜːtʃ/
v. 搜查，搜寻；搜查（地方，车辆），搜……的身；思索，细想（问题答案等）；细察，细查；（用计算机）搜索，检索
n. 搜寻，搜查；探索，寻求；（计算机的）搜索，检索；<律>调查地产负担

[^12]: replacement /rɪˈpleɪsmənt/
n. 代替，更换；取代（或代替）的人（或物）；补充兵员

[^13]: replace /rɪˈpleɪs/
v. 取代；（用……）替换，（以……）接替；更换， 赔还；把…放回原处

[^14]: substituted /ˈsʌbstɪtju:tɪd/
adj. 取代的，代替的
v. 代替；用……代替（substitute 的过去式）

[^15]: terminate /ˈtɜːmɪneɪt/
v.（使）结束，（使）终止；到达终点站；终止妊娠，人工流产；<美>解雇；<美>谋杀（某人）；在……结尾，以……收尾
adj. 结束的

[^16]: greater /greɪtə®/
adj. 较大的（great 的比较级）

许可协议

This article is licensed under an Attribution-NonCommercial-ShareAlike 4.0 International licence, except where otherwise noted.

本文采用 署名-非商业性使用-相同方式共享 4.0 国际 许可协议，转载请注明出处。

分享文章