• Structure of a C program: Preprocessor directives (#include <stdlib.h>, #define)


     Preprocessor programs provide preprocessors directives which tell the compiler to preprocess the source code before compiling.

    Examples of some preprocessor directives are: #include#define#ifndef etc.

    There are 4 main types of preprocessor directives:

    1. Macros
    2. File Inclusion
    3. Conditional Compilation
    4. Other directives

    Macros

    #include <stdio.h> 
    
    // macro definition 
    #define LIMIT 5 
    int main() 
    { 
        for (int i = 0; i < LIMIT; i++) { 
            printf("%d \n",i); 
        } 
    
        return 0; 
    } 

    File Inclusion

    1.Header File or Standard files: These files contains definition of pre-defined functions like printf(), scanf() etc.

    #include< file_name >

    2.user defined files: When a program becomes very large, it is good practice to divide it into smaller files and include whenever needed. These types of files are user defined files. These files can be included as:

    #include"filename"

    Conditional Compilation:

    Conditional Compilation directives are type of directives which helps to compile a specific portion of the program or to skip compilation of some specific part of the program based on some conditions. This can be done with the help of two preprocessing commands ‘ifdef‘ and ‘endif‘.

    #ifdef macro_name
        statement1;
        statement2;
        statement3;
        .
        .
        .
        statementN;
    #endif

    If the macro with name as ‘macroname‘ is defined then the block of statements will execute normally but if it is not defined, the compiler will simply skip this block of statements.

    Other directives

    #undef Directive: The #undef directive is used to undefine an existing macro. This directive works as:

    #undef LIMIT

    Using this statement will undefine the existing macro LIMIT. After this statement every “#ifdef LIMIT” statement will evaluate to false.

  • 相关阅读:
    Java中使用Base64编码URL
    JSON Web Token (JWT)入门学习
    1047. 删除字符串中的所有相邻重复项
    1021. 删除最外层的括号
    使用shell获取随机端口<帮你解决端口的占用烦恼>
    初始化一个vue项目并生成完整的目录结构
    mysql-常用字符函数
    设计模式-单例模式-饿汉和懒汉
    Java-指令的重排序
    Java-反射类加载到内存分析
  • 原文地址:https://www.cnblogs.com/JasperZhao/p/12897927.html
Copyright © 2020-2023  润新知