HeaderFiles.ipynb

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    "# Header Files\n",
    "\n",
    "- header files and their purpose\n",
    "- standard library header files\n",
    "- header file content rules\n",
    "- using header files\n",
    "- implementation files"
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    "## Header files and their purposes\n",
    "\n",
    "- we've used library header files such as `iostream`, `string`, etc.\n",
    "- the purpose of this chapter is to learn how to create your own header files and why\n",
    "- as program grows bigger, code need to be divided into many files\n",
    "- using function prototype (forward declaration) and defining functions after main is not scalable\n",
    "- breaking solution code into many files has many advantages:\n",
    "    - makes program easier to manage, read, update, debug\n",
    "    - makes it easier to work in a team where each member works on a separate file\n",
    "    - avoid conflicts while using version control such as git\n",
    "\n",
    "- Generally, header files allow us to put declarations in one or more files and then include them wherever we need them\n",
    "    - this can save a lot of typing in multi-file programs\n",
    "    - helps us create our own library of important functions\n",
    "    \n",
    "## Creating header files\n",
    "- header best practices:\n",
    "    - must contain header include guards (to avoid being included multiple times in the final binary)\n",
    "    - typically contains struct and class definitions only\n",
    "    - contains function prototypes\n",
    "    - avoid function definitions\n",
    "    - may include other header files\n",
    "    - do NOT declare global variables \n",
    "    - each header file should be as independent as possible with specific purpose\n",
    "    - file has `.h` extension\n",
    "    \n",
    "## Implementing header files\n",
    "- typically a header file is implmented in a separate corresponding .cpp file\n",
    "- functions and classes are implmented or defined in implementation files\n",
    "- implementation file are regular .cpp files that must include the header being implemented\n",
    "- must also include any library header files required to implment the functions\n",
    "- syntax:\n",
    "\n",
    "```cpp\n",
    "    #include \"headerFileName.h\"\n",
    "```\n",
    "- note the double quotes `\"headerName.h\"` instead of `<headerName.h>` used for built-in headers\n",
    "    \n",
    "## Using header files\n",
    "- include user-defined header files similar to library header file\n",
    "- include only the header files that are required\n",
    "- syntax:\n",
    "\n",
    "```cpp\n",
    "    #include \"headerFileName.h\"\n",
    "```\n",
    "- use the functions and user-defined types, etc. defined in the included header file\n",
    "\n",
    "## Compiling multiple cpp files\n",
    "- header files are not compiled; ONLY the CPP files\n",
    "- compiling multiple file is similar to compiling single file using g++ compiler\n",
    "    - simply list all the .cpp files separated by a space\n",
    "\n",
    "```bash\n",
    "    g++ <switches: -std=c++17, etc.> -o programName inputFile1.cpp inputFile2.cpp ...\n",
    "```\n",
    "- or use the Makefile as shown in the following demo programs\n",
    "\n",
    "### Demo 1 - see folder [demos/header_files/header/](demos/header_files/header/)\n",
    "- a simple demo program with one header file\n",
    "\n",
    "### Demo 2 - see folder [demos/header_files/triangle/](demos/header_files/triangle/)\n",
    "- contains several header and cpp files\n",
    "- a single-file `triangle.cpp` program provided in File IO chapter - [demos/file_io/triangle/](demo_programs/file_io/triangle/) is separated into several `header` and `cpp` files\n",
    "- test functions are separated into `test.h` and `test.cpp` files\n",
    "- utility functions are separated into `utility.h` and `utility.cpp` files\n",
    "- main entry/driver function is in `main.cpp` file\n",
    "- triangle definition and related functions are separated into `triangle.h` and `triangle.cpp` files"
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