Understanding the Standard Library and Files in C++

Standard libraries serve as repositories of prewritten, reusable code that simplifies common tasks. They save developers time and effort by offering well-tested, standardized tools for building software.

Basically, they are just files that you can include in your project. Some of them cover essential tasks like outputting information or working with text, while others are more specific and cover areas like networking. Here is the source code for some of them:

iostream

iomanip

string

// Standard iostream objects -*- C++ -*-

// Free Software Foundation, Inc.

// This file is part of the GNU ISO C++ Library. This library is free

// software; you can redistribute it and/or modify it under the

// terms of the GNU General Public License as published by the

// Free Software Foundation; either version 3, or (at your option)

// any later version.

// This library is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional

// permissions described in the GCC Runtime Library Exception, version

// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and

// a copy of the GCC Runtime Library Exception along with this program;

// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see

// <http://www.gnu.org/licenses/>.

/** @file include/iostream

* This is a Standard C++ Library header.

// ISO C++ 14882: 27.3 Standard iostream objects

#ifndef _GLIBCXX_IOSTREAM

#define _GLIBCXX_IOSTREAM 1


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// Standard iostream objects -*- C++ -*-

// Copyright (C) 1997, 1998, 1999, 2001, 2002, 2005, 2008, 2009, 2010
// Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file include/iostream
 *  This is a Standard C++ Library header.
 */

//
// ISO C++ 14882: 27.3  Standard iostream objects
//

#ifndef _GLIBCXX_IOSTREAM
#define _GLIBCXX_IOSTREAM 1

#pragma GCC system_header

#include <bits/c++config.h>
#include <ostream>
#include <istream>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   *  @name Standard Stream Objects
   *
   *  The <iostream> header declares the eight <em>standard stream
   *  objects</em>.  For other declarations, see
   *  http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch24.html
   *  and the @link iosfwd I/O forward declarations @endlink
   *
   *  They are required by default to cooperate with the global C
   *  library's @c FILE streams, and to be available during program
   *  startup and termination. For more information, see the HOWTO
   *  linked to above.
   */
  //@{
  extern istream cin;       /// Linked to standard input
  extern ostream cout;      /// Linked to standard output
  extern ostream cerr;      /// Linked to standard error (unbuffered)
  extern ostream clog;      /// Linked to standard error (buffered)

#ifdef _GLIBCXX_USE_WCHAR_T
  extern wistream wcin;     /// Linked to standard input
  extern wostream wcout;    /// Linked to standard output
  extern wostream wcerr;    /// Linked to standard error (unbuffered)
  extern wostream wclog;    /// Linked to standard error (buffered)
#endif
  //@}

  // For construction of filebuffers for cout, cin, cerr, clog et. al.
  static ios_base::Init __ioinit;

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif /* _GLIBCXX_IOSTREAM */

Why to use Standard Libraries and Files

Writing code with a library is like a writing a book with a dictionary. We can easily replace a phrase with only one word without losing the main meaning

Low level		High level
In a biological community where organisms interact with their physical environment, everything has to be in a situation in which different elements are equal or in the correct proportions.		In an ecosystem, everything has to be in balance.

You can rewrite this using already existing terms from a dictionary. Similar to using existing library, you can reduce hundreds of lines of code to just a single one using a library.

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Section 1. Chapter 3

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