File Header Structure and Includes

License header: All files start with the ADIOS2 Apache license header, file name, creation date, and author's name. Contact information is encouraged.

/*
 * Distributed under the OSI-approved Apache License, Version 2.0.  See
 * accompanying file Copyright.txt for details.
 *
 * MyClass.h
 *
 *  Created on: April 27, 2017
 *      Author: Mark Alexander Godoy  godoyma@email.com
 */

Header files include guards: All header files must have include guards to prevent name conflict. These are placed right after the license and at the end of the file. The adopted format includes the relative path in ADIOS. For example, the file adios2/engine/bp/BPFileWriter.h will contain the following include guards:
```
#ifndef  ADIOS2_ENGINE_BP_BPFILEWRITER_H_
#define  ADIOS2_ENGINE_BP_BPFILEWRITER_H_
//File contents...
...

//End of file
#endif  // ADIOS2_ENGINE_BP_BPFILEWRITER_H_
```

Document included headers: List header components used in the code if header is not self-explanatory. Example:

//vector and map are self-explanatory, no comment needed
#include <map>
#include <stdexcept>  //std::invalid_argument
#include <utility>    //std::pair
#include <vector>

Header includes organization: Seperate included headers into the following groups: Example for file ClassName.cpp:
- Corresponding header: ClassName.h
- System C headers: sys/ipc.h, unistd.h, windows.h
- C++ Wrapped ISO C headers: cmath, cstring
- C++ headers: map, thread, vector
- External libraries: zfp.h, bzip2.h
- ADIOS2 headers: adios2/ADIOSMPI.h, adios2/ADIOSTypes.h
Each group should be seperated by a newline and the headers alphabetically sorted within that group. Use #include "foo.h" for headers part of ADIOS2 and #include <foo.h> for all others.
```
#include "ClassName.h"

#ifdef WIN32
#include <windows.h> // CreateProcess, CreateNamedPipe
#else
#include <sys/ipc.h> //ftok
#include <unistd.h>  //key_t
#endif

#include <cmath>   // sqrt
#include <cstring> // memcpy, memset

#include <map>
#include <thread>
#include <vector>

#ifdef ADIOS2_HAVE_ZFP
#include <zfp.h>
#endif

#ifdef ADIOS2_HAVE_BZIP2
#include <bzip2.h>
#endif

#include "adios2/ADIOSMPI.h"
#include "adios2/ADIOSTypes.h"
```