{"id":3248,"date":"2024-05-10T11:46:34","date_gmt":"2024-05-10T11:46:34","guid":{"rendered":"https:\/\/www.skillvertex.com\/blog\/?p=3248"},"modified":"2024-05-10T11:46:34","modified_gmt":"2024-05-10T11:46:34","slug":"header-files-in-c-c-and-its-uses","status":"publish","type":"post","link":"https:\/\/www.skillvertex.com\/blog\/header-files-in-c-c-and-its-uses\/","title":{"rendered":"Header Files In C\/C++ And Its Uses"},"content":{"rendered":"\n<div class=\"wp-block-rank-math-toc-block\" id=\"rank-math-toc\" id=\"rank-math-toc\"><p>Table of Contents<\/p><nav><ul><li ><a href=\"#header-files-in-c-c-and-its-uses\">Header Files In C\/C++ And Its Uses<\/a><\/li><li ><a href=\"#syntax-of-header-file-in-c-c\">Syntax Of Header File In C\/C+<\/a><\/li><li ><a href=\"#types-of-header-files\">Types of Header Files<\/a><\/li><li ><a href=\"#1-standard-header-files-in-c-and-their-uses\">1. Standard Header Files in C and their Uses<\/a><\/li><li ><a href=\"#2-non-standard-header-files-in-c-and-their-uses\">2. Non-Standard Header Files in C and Their Uses<\/a><\/li><li ><a href=\"#2-non-standard-header-files-in-c-and-their-uses-1\">2. Non-Standard Header Files in C and Their Uses<\/a><\/li><li ><a href=\"#standard-header-files-in-c-and-their-uses\">Standard Header Files in C++ and their Uses<\/a><\/li><li ><a href=\"#c-languages-standard-libraries-are-the-following\">C language\u2019s Standard Libraries are the following<\/a><\/li><li ><a href=\"#non-standard-header-files-in-c-and-their-uses\">Non-Standard Header Files in C++ and Their Uses<\/a><\/li><li ><a href=\"#create-your-own-header-file-in-c-and-c\">Create your own Header File in C and C++<\/a><\/li><li ><a href=\"#including-multiple-header-files\">Including Multiple Header Files<\/a><\/li><li ><a href=\"#faq-header-files-in-c-c-and-its-uses\">FAQ- Header Files In C\/C++ And Its Uses<\/a><\/li><\/ul><\/nav><\/div>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"header-files-in-c-c-and-its-uses\">Header Files In C\/C++ And Its Uses<\/h2>\n\n\n\n<p>Header files are an essential part of both programming languages, and they serve as a means to include predefined standard library functions, data types, macros, and other features in your programs.In C, header files typically have the &#8220;.h&#8221; extension, and you include them in your code using the #include preprocessor directive. These header files provide access to various libraries and functions to simplify programming.<\/p>\n\n\n\n<p>In C++, header files may or may not have the &#8220;.h&#8221; extension. The #include directive is used to import these header files and access the features they provide, including library functions, data types, and macros.These preprocessor directives are vital in both languages, as they ensure that the necessary header files are processed before the actual compilation, making the required features available for your code.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"syntax-of-header-file-in-c-c\">Syntax Of Header File In C\/C+<\/h2>\n\n\n\n<pre class=\"wp-block-code\"><code>#include &lt;filename.h&gt;    \/\/ for files in system\/default directory\n       or\n#include \"filename.h\"    \/\/ for files in same directory as source file<\/code><\/pre>\n\n\n\n<p>The #include directive instructs the compiler to process the specified header file before the actual compilation of the source code. This includes making available all the necessary data types, function definitions, and other declarations contained within the included header file for use in your program. It allows you to access predefined functionality and libraries to simplify your programming tasks.<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\n\/\/ C program to demonstrate the use of header files\n\/\/    standard input and output stdio.h header file\n#include &lt;stdio.h&gt;\n \nint main()\n{\n    printf(\n        \"Printf() is the function in stdio.h header file\");\n    return 0;\n}<\/code><\/pre>\n\n\n\n<p>Output<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>Printf() is the function in stdio.h header file\n<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"types-of-header-files\">Types of Header Files<\/h2>\n\n\n\n<p>There are two types of header files in C and C++:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Standard \/ Pre-existing header files<\/strong><\/li>\n\n\n\n<li><strong>Non-standard \/ User-defined header files<\/strong><\/li>\n<\/ol>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"1-standard-header-files-in-c-and-their-uses\">1. Standard Header Files in C and their Uses<\/h2>\n\n\n\n<p>Standard header files contain libraries and functions that are defined in the ISO standard of the C programming language. These header files are typically stored in the default directory of the C compiler, making them universally accessible and present in all C compilers from different vendors. This standardization ensures that C programs can be written and compiled consistently across different platforms and compilers, making it a powerful feature of the C programming language.<\/p>\n\n\n\n<p>There are 31 standard header files in the latest version of C language.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Header File<\/th><th>Description<\/th><\/tr><\/thead><tbody><tr><td>&lt;assert.h&gt;<\/td><td>It has information regarding adding diagnostics that aid program debugging.<\/td><\/tr><tr><td>&lt;errorno.h&gt;<\/td><td>It has to perform&nbsp;<a href=\"https:\/\/www.geeksforgeeks.org\/error-handling-c-programs\/\" rel=\"nofollow noopener\" target=\"_blank\">error-handling<\/a>&nbsp;operations like errno(), strerror(), perror(), etc.<\/td><\/tr><tr><td><a href=\"https:\/\/www.geeksforgeeks.org\/cfloat-float-h-in-c-c-with-examples\/\" rel=\"nofollow noopener\" target=\"_blank\">&lt;float.h&gt;<\/a><\/td><td>It has to perform&nbsp;<a href=\"https:\/\/www.geeksforgeeks.org\/error-handling-c-programs\/\" rel=\"nofollow noopener\" target=\"_blank\">error-handling<\/a>&nbsp;operations like errno(), strerror(), perror(), etc.<\/td><\/tr><tr><td><a href=\"https:\/\/www.geeksforgeeks.org\/c-library-math_h\/\" rel=\"nofollow noopener\" target=\"_blank\">&lt;math.h&gt;<\/a><\/td><td>It has to perform mathematical operations like&nbsp;<a href=\"https:\/\/www.geeksforgeeks.org\/sqrt-sqrtl-sqrtf-cpp\/\" rel=\"nofollow noopener\" target=\"_blank\">sqrt()<\/a>,&nbsp;<a href=\"https:\/\/www.geeksforgeeks.org\/log2-function-in-c-with-examples\/\" rel=\"nofollow noopener\" target=\"_blank\">log2()<\/a>,&nbsp;<a href=\"https:\/\/www.geeksforgeeks.org\/power-function-cc\/\" rel=\"nofollow noopener\" target=\"_blank\">pow()<\/a>, etc.<\/td><\/tr><tr><td>&lt;signal.h&gt;<\/td><td>It has to perform signal handling functions like signal() and raise().<\/td><\/tr><tr><td>&lt;stdarg.h&gt;<\/td><td>It has to perform standard argument functions like va_start() and va_arg(). Moreover, they are used to indicate the start of the variable-length argument list and to get the arguments from the variable-length argument list in the program respectively.<\/td><\/tr><tr><td><a href=\"https:\/\/www.geeksforgeeks.org\/ctype-hcctype-library-in-c-c-with-examples\/\" rel=\"nofollow noopener\" target=\"_blank\">&lt;ctype.h&gt;<\/a><\/td><td>It has function prototypes for functions that will test characters for certain properties and also function prototypes for&nbsp;functions that will be used to convert uppercase letters to lowercase letters and vice versa.<br>&nbsp;<\/td><\/tr><tr><td>&lt;stdio.h&gt;<\/td><td>&lt;stdio.h&gt; functions to perform input and output operations using functions like&nbsp;<a href=\"https:\/\/www.geeksforgeeks.org\/scanf-and-fscanf-in-c-simple-yet-poweful\/\" rel=\"nofollow noopener\" target=\"_blank\">scanf()<\/a>,&nbsp;<a href=\"https:\/\/www.geeksforgeeks.org\/return-values-of-printf-and-scanf-in-c-cpp\/\" rel=\"nofollow noopener\" target=\"_blank\">printf()<\/a>, etc.<\/td><\/tr><tr><td>&lt;setjump.h&gt;<\/td><td>It even contains standard utility functions like malloc(), realloc(), etc. It contains function prototypes for functions that allow bypassing&nbsp;of the usual function call and return sequence.<\/td><\/tr><tr><td>&lt;string.h&gt;<\/td><td>It determines the various properties of the various variable types. The macros defined in this header limit the values of&nbsp;various variable types like char, int, and long. These limits specify that a variable cannot store any value&nbsp;beyond these limits, for example, an unsigned character can store up to a maximum value of 255.<\/td><\/tr><tr><td><a href=\"https:\/\/www.geeksforgeeks.org\/climits-limits-h-cc\/\" rel=\"nofollow noopener\" target=\"_blank\">&lt;limits.h&gt;<\/a><\/td><td>It determines the various properties of the various variable types. The macros defined in this header limits the values of&nbsp;various variable types like char, int, and long. These limits specify that a variable cannot store any value&nbsp;beyond these limits, for example, an unsigned character can store up to a maximum value of 255.<\/td><\/tr><tr><td><a href=\"https:\/\/www.geeksforgeeks.org\/time-h-header-file-in-c-with-examples\" rel=\"nofollow noopener\" target=\"_blank\">&lt;time.h&gt;<\/a><\/td><td>It will perform functions related to date() and&nbsp;<a href=\"https:\/\/www.geeksforgeeks.org\/time-function-in-c\/\" rel=\"nofollow noopener\" target=\"_blank\">time()<\/a>&nbsp;like&nbsp;<a href=\"https:\/\/www.geeksforgeeks.org\/getdate-and-setdate-function-in-c-with-examples\/\" rel=\"nofollow noopener\" target=\"_blank\">setdate()<\/a>&nbsp;and&nbsp;<a href=\"https:\/\/www.geeksforgeeks.org\/getdate-and-setdate-function-in-c-with-examples\/\" rel=\"nofollow noopener\" target=\"_blank\">getdate()<\/a>. It is also used to modify the system date&nbsp;and get the CPU time respectively.<\/td><\/tr><tr><td>&lt;stddef.h&gt;<\/td><td>It will contain common type definitions used by C for performing calculations.<\/td><\/tr><tr><td>&lt;locale.h&gt;<\/td><td>It will  contain function prototypes and other information that enables a program to be modified for the current locale on which it\u2019s running.&nbsp;It enables the computer system to handle different conventions for expressing data such as times, dates, or large numbers throughout the world.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>Example<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/ C program to illustrate\n\/\/ the use of header file\n\/\/ in C\n#include &lt;math.h&gt;\n#include &lt;stdio.h&gt;\n#include &lt;stdlib.h&gt;\n#include &lt;string.h&gt;\n \n\/\/ Driver Code\nint main()\n{\n    char s1&#91;20] = \"12345\";\n    char s2&#91;10] = \"Geeks\";\n    char s3&#91;10] = \"ForGeeks\";\n    long int res;\n \n    \/\/ Find the value of 9^3 using a\n    \/\/ function in math.h library\n    res = pow(9, 3);\n    printf(\"Using math.h, \"\n           \"The value is: %ld\\n\",\n           res);\n \n    \/\/ Convert a string to long long int\n    \/\/ using a function in stdlib.h library\n    long int a = atol(s1);\n    printf(\"Using stdlib.h, the string\");\n    printf(\" to long int: %ld\\n\", a);\n \n    \/\/ Copy the string s3 into s2 using\n    \/\/ using a function in string.h library\n    strcpy(s2, s3);\n    printf(\"Using string.h, the strings\"\n           \" s2 and s3: %s %s\\n\",\n           s2, s3);\n    return 0;\n}<\/code><\/pre>\n\n\n\n<p>Output<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>Using math.h, The value is: 729\nUsing stdlib.h, the string to long int: 12345\nUsing string.h, the strings s2 and s3: Skill Vertex<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"2-non-standard-header-files-in-c-and-their-uses\">2. Non-Standard Header Files in C and Their Uses<\/h2>\n\n\n\n<p>Non-standard header files are not part of the ISO standard of the C programming language. These header files are typically created by programmers for various purposes, such as containing custom library functions or platform-specific code. They are not part of the standard library and are not guaranteed to be available on all C compilers.<\/p>\n\n\n\n<p>Non-standard header files can be manually installed by the user, included as part of a third-party library, or provided by specific vendors. Their use is often limited to specific projects or platforms and may not be portable across different environments or compilers.<\/p>\n\n\n\n<p>&nbsp;Some commonly used non-standard\/user-defined header files are listed below:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Header File<\/th><th>Description<\/th><\/tr><\/thead><tbody><tr><td>&lt;conio.h&gt;<\/td><td>It has  some useful console functions.<\/td><\/tr><tr><td>&lt;gtk\/gtk.h&gt;<\/td><td>It has some useful console functions.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"2-non-standard-header-files-in-c-and-their-uses-1\">2. Non-Standard Header Files in C and Their Uses<\/h2>\n\n\n\n<p>Non-standard header files are not included in the official ISO standard for the C programming language. These header files are typically created by programmers for various purposes, including custom library functions or platform-specific code. They are not guaranteed to be universally available, and their use is often limited to specific projects, user installations, or specific compiler distributions by certain vendors. Non-standard header files provide a way to extend the functionality of C for specific use cases but may not be portable across different environments or compilers.<\/p>\n\n\n\n<p>There are various non-standard libraries for C language. Some are commonly used non-standard\/user-defined header files are listed below:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Header File<\/th><th>Description<\/th><\/tr><\/thead><tbody><tr><td>&lt;conio.h&gt;<\/td><td>It has some useful console functions.<\/td><\/tr><tr><td>&lt;gtk\/gtk.h&gt;<\/td><td>It has GNU\u2019s GUI library for C.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"standard-header-files-in-c-and-their-uses\">Standard Header Files in C++ and their Uses<\/h2>\n\n\n\n<p>Standard header files in C++ contain libraries and functionalities that are part of the C++ ISO standard. These header files come pre-installed with the C++ compiler from any vendor, ensuring that they are universally available for C++ programmers.<\/p>\n\n\n\n<p>You can include these standard header files in your C++ programs using the <code>#include<\/code> preprocessor directive. This allows you to access the standard libraries, data types, and functions defined by the C++ ISO standard in your code, making it easier to write portable and standardized C++ programs across different platforms and compilers.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"c-languages-standard-libraries-are-the-following\">C language\u2019s Standard Libraries are the following<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Header File<\/th><th>Description<\/th><\/tr><\/thead><tbody><tr><td>&lt;iostream&gt;<\/td><td>It  has a stream of Input and Output using cin and cout.<\/td><\/tr><tr><td>&lt;iomanip&gt;<\/td><td>It has a stream of Input and Output using cin and cout.<\/td><\/tr><tr><td>&lt;fstream&gt;<\/td><td>It functions to control the data to read from a file as an input and data to write into the file as an output.<\/td><\/tr><tr><td><a href=\"https:\/\/www.geeksforgeeks.org\/c-magicians-stl-algorithms\/\" rel=\"nofollow noopener\" target=\"_blank\">&lt;algorithm&gt;<\/a><\/td><td>It has some useful algorithms which are part of STL.<\/td><\/tr><tr><td>&lt;new&gt;<\/td><td>It has a  dynamic memory allocation methods.<\/td><\/tr><tr><td><a href=\"https:\/\/www.geeksforgeeks.org\/vector-in-cpp-stl\/\" rel=\"nofollow noopener\" target=\"_blank\">&lt;vector&gt;<\/a><\/td><td>It has the definition of the vector class container of STL.<\/td><\/tr><tr><td><a href=\"https:\/\/www.geeksforgeeks.org\/map-associative-containers-the-c-standard-template-library-stl\/\" rel=\"nofollow noopener\" target=\"_blank\">&lt;map&gt;<\/a><\/td><td>It has a  dynamic memory allocation method.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>Example<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\n\n\/\/ C++ program to demonstrate the use of standard header\n\/\/ files in c++\n#include &lt;iostream&gt;\n#include &lt;vector&gt;\n \nusing namespace std;\n \n\/\/ driver code\nint main()\n{\n    \/\/ cout is defined in &lt;iostream&gt;\n    cout &lt;&lt; \"Using iostream's cout to print\" &lt;&lt; endl;\n \n    \/\/ vector defined in &lt;vector&gt; header file\n    vector&lt;int&gt; v{ 11, 12, 14 };\n \n    cout &lt;&lt; \"Using vector container: \";\n    for (auto i : v) {\n        cout &lt;&lt; i &lt;&lt; \" \";\n    }\n    return 0;\n}<\/code><\/pre>\n\n\n\n<p>Output<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>Using iostream's cout to print\nUsing vector container: 11 12 14<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"non-standard-header-files-in-c-and-their-uses\">Non-Standard Header Files in C++ and Their Uses<\/h2>\n\n\n\n<p>Non-standard header files are not included in the ISO standard of C++, and they are typically created by programmers for their specific needs. These header files are not part of the official standard library and are not guaranteed to be universally available.<\/p>\n\n\n\n<p>Non-standard header files can be manually installed by the user or included as part of a specific compiler distribution by a vendor. They are often used to extend the functionality of C++ for particular projects, but their availability may be limited to specific environments or compilers.<\/p>\n\n\n\n<p><strong>some non-standard header files in C++<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Header File<\/th><th>Description<\/th><\/tr><\/thead><tbody><tr><td><a href=\"https:\/\/www.geeksforgeeks.org\/bitsstdc-h-c\/\" rel=\"nofollow noopener\" target=\"_blank\">&lt;bits\/stdc++.h&gt;<\/a><\/td><td>It has all the standard libraries of the header files mentioned above. However, if you include it in your code, then you need not have to&nbsp;include any other standard header files. But as it is a non-standard header file of GNU C++ library, so, if you try to compile your&nbsp;code with some compiler other than GCC it might fail; e.g. MSVC does not have this header.<\/td><\/tr><tr><td>&lt;Qpushbutton&gt;<\/td><td>It has a push button element of Qt GUI Library for C++<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>Example<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/ C++ program to illustrate the use of\n\/\/ non-standard bits\/stdc++.h header file in C++\n#include &lt;bits\/stdc++.h&gt;\nusing namespace std;\n \n\/\/ Driver Code\nint main()\n{\n \n    char s1&#91;20] = \"12345\";\n    char s2&#91;10] = \"Geeks\";\n    char s3&#91;10] = \"ForGeeks\";\n    long int res;\n \n    \/\/ All the below function are mentioned in bits\/stdc++.h\n    \/\/ library Find the value of 9^3\n    res = pow(9, 3);\n    cout &lt;&lt; \"Using bits\/stdc++.h, \"\n            \"The value is: \"\n         &lt;&lt; res &lt;&lt; \"\\n\";\n \n    \/\/ Convert a string to long long int\n    long int a = atol(s1);\n    cout &lt;&lt; \"Using bits\/stdc++.h, the string\";\n    cout &lt;&lt; \" to long int: \" &lt;&lt; a &lt;&lt; \"\\n\";\n \n    \/\/ Copy the string s3 into s2 using\n    strcpy(s2, s3);\n    cout &lt;&lt; \"Using bits\/stdc++.h, the strings\"\n            \" s2 and s3: \"\n&lt;&lt; s2 &lt;&lt; s3 &lt;&lt; \"\\n\";\n \n    return 0;\n}<\/code><\/pre>\n\n\n\n<p>Output<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>Using bits\/stdc++.h, The value is: 729\nUsing bits\/stdc++.h, the string to long int: 12345\nUsing bits\/stdc++.h, the strings s2 and s3: Skill Vertex<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"create-your-own-header-file-in-c-and-c\">Create your own Header File in C and C++<\/h2>\n\n\n\n<p>Custom header files are a useful way to organize and modularize your code, making it more readable and maintainable. The steps you provided for creating a custom header file are generally correct:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Write your own C\/C++ code and save it with a &#8220;.h&#8221; extension. This is how you create the header file, and it typically contains function declarations, data type definitions, and other declarations that you want to use in multiple parts of your program.<\/li>\n<\/ol>\n\n\n\n<p>By following this process, you can create your own reusable code modules, which can enhance code functionality, improve code organization, and make your programs more readable and manageable. These custom header files are included in your programs using the <code>#include<\/code> preprocessor directive, allowing you to access the declared functions and data types when needed.<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\n\/\/ Function to find the sum of two\n\/\/ numbers passed\nint sumOfTwoNumbers(int a, int b) \n{\n  return (a + b); \n}<\/code><\/pre>\n\n\n\n<p><strong>Step 2:<\/strong>&nbsp;We have to include your header file with&nbsp;<strong>\u201c#include\u201d<\/strong>&nbsp;in your C\/C++ program as provided<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\n\n\/\/ C++ program to find the sum of two\n\/\/ numbers using function declared in\n\/\/ header file\n#include \"iostream\"\n \n\/\/ Including header file\n#include \"sum.h\"\nusing namespace std;\n \n\/\/ Driver Code\nint main()\n{\n \n    \/\/ Given two numbers\n    int a = 13, b = 22;\n \n    \/\/ Function declared in header\n    \/\/ file to find the sum\n    printf(\"Sum is: %d\", sumoftwonumbers(a, b));\n}<\/code><\/pre>\n\n\n\n<p>Output<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>Sum is : 35\nProcess returned  0  (O x O) execution time:  0.287 s \nPress any key and continue\n<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"including-multiple-header-files\">Including Multiple Header Files<\/h2>\n\n\n\n<p>When you include a header file more than once in a program, the contents of the header file are processed multiple times, which can lead to errors due to redefinition of symbols and declarations. To prevent these errors, conditional preprocessor directives, such as <code>#ifndef<\/code>, <code>#define<\/code>, and <code>#endif<\/code>, are commonly used to ensure that the header file is only processed once.<\/p>\n\n\n\n<p>Syntax:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>#ifndef HEADER_FILE_NAME\n#define HEADER_FILE_NAME\n\nthe entire header file\n\n#endi<\/code><\/pre>\n\n\n\n<p>This construct is referred to as the wrapper&nbsp;<strong>\u201c#ifndef\u201d<\/strong>. Whenever the header is included again, the conditional will be false, as &nbsp;<strong>HEADER_FILE_NAME<\/strong>&nbsp;will be defined. The preprocessor will skip over the entire file contents, and the compiler will not see it twice.<\/p>\n\n\n\n<p>Sometimes it\u2019s important to have several diverse header files based on the requirements of the program. For this, multiple conditionals will be used.<\/p>\n\n\n\n<p>Syntax:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>#if SYSTEM_ONE\n        #include \"system1.h\"\n#elif SYSTEM_TWO\n        #include \"system2.h\"\n#elif SYSTEM_THREE\n        ....\n#endif<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"faq-header-files-in-c-c-and-its-uses\">FAQ- Header Files In C\/C++ And Its Uses<\/h2>\n\n\n<div id=\"rank-math-faq\" class=\"rank-math-block\">\n<div class=\"rank-math-list \">\n<div id=\"faq-question-1699012609535\" class=\"rank-math-list-item\">\n<h4 class=\"rank-math-question \">Q1. What are header files in C++ and their use?<\/h4>\n<div class=\"rank-math-answer \">\n\n<p>Ans. Header files in C++ offer code reusability, organization, and complexity reduction. They allow you to declare functions and data types once and use them in various parts of your program, simplifying code and reducing errors.<\/p>\n\n<\/div>\n<\/div>\n<div id=\"faq-question-1699012620136\" class=\"rank-math-list-item\">\n<h4 class=\"rank-math-question \">Q2. Can C header files be used in C++?<\/h4>\n<div class=\"rank-math-answer \">\n\n<p>Ans.When including a C header file in a C++ program, you may need to use the <code>extern \"C\"<\/code> construct to inform the C++ compiler that the functions declared in the header file are C functions. This is necessary because C and C++ have different name mangling conventions, and using <code>extern \"C\"<\/code> ensures that the functions are treated as C functions with C linkage, making them compatible with C++ code.<\/p>\n\n<\/div>\n<\/div>\n<div id=\"faq-question-1699012628812\" class=\"rank-math-list-item\">\n<h4 class=\"rank-math-question \">Q3. What are the header files in C and their function?<\/h4>\n<div class=\"rank-math-answer \">\n\n<p>Ans. Header files in C have the &#8220;.h&#8221; extension and contain function declarations and macros for sharing among different source files. There are two types: custom ones created by programmers and standard ones provided by the compiler for common functionality.<\/p>\n\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n\n\n<h2 class=\"wp-block-heading\"><br><\/h2>\n","protected":false},"excerpt":{"rendered":"<p>Header Files In C\/C++ And Its Uses Header files are an essential part of both programming languages, and they serve as a means to include predefined standard library functions, data types, macros, and other features in your programs.In C, header files typically have the &#8220;.h&#8221; extension, and you include them in your code using the &#8230; <a title=\"Header Files In C\/C++ And Its Uses\" class=\"read-more\" href=\"https:\/\/www.skillvertex.com\/blog\/header-files-in-c-c-and-its-uses\/\" aria-label=\"More on Header Files In C\/C++ And Its Uses\">Read more<\/a><\/p>\n","protected":false},"author":4,"featured_media":3250,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[27],"tags":[539],"class_list":["post-3248","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-c-programming","tag-header-files-in-c-c-and-its-uses","generate-columns","tablet-grid-50","mobile-grid-100","grid-parent","grid-33"],"_links":{"self":[{"href":"https:\/\/www.skillvertex.com\/blog\/wp-json\/wp\/v2\/posts\/3248","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.skillvertex.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.skillvertex.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.skillvertex.com\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.skillvertex.com\/blog\/wp-json\/wp\/v2\/comments?post=3248"}],"version-history":[{"count":7,"href":"https:\/\/www.skillvertex.com\/blog\/wp-json\/wp\/v2\/posts\/3248\/revisions"}],"predecessor-version":[{"id":10754,"href":"https:\/\/www.skillvertex.com\/blog\/wp-json\/wp\/v2\/posts\/3248\/revisions\/10754"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.skillvertex.com\/blog\/wp-json\/wp\/v2\/media\/3250"}],"wp:attachment":[{"href":"https:\/\/www.skillvertex.com\/blog\/wp-json\/wp\/v2\/media?parent=3248"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.skillvertex.com\/blog\/wp-json\/wp\/v2\/categories?post=3248"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.skillvertex.com\/blog\/wp-json\/wp\/v2\/tags?post=3248"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}