Cross platform coding issues in C++ for Windows/linux

Some of code issues traced and workout for Windows/linux by C++

1. Accessing system related functionalities:

• Windows and Linux have following different memory structure. So need to develop separate code for these platform
• for example:
  #include <sys/sysinfo.h>
  ..
  struct sysinfo memInfo; //used to get memory info
  …
  In windows compilation it raised error. So, This function is Linux-specific, and should not be used in programs intended to be portable.
• To get Windows related memory structure, include ‘Windows.h’
• ..Tips to skip compilation error following lines can be used:
  #ifdef __linux__
  //
  #else
  //
  #endif

 

2. Unordered map:

• Normal code:
  #include <unordered_map>
  …
  unordered_map<long,long> map_FAZIT3130;
• Cross platform code:
  #include <tr1/unordered_map>
  using namespace std::tr1;
  …
  unordered_map<long,long> map_FAZIT3130;

 

3. Threads:

• Compiler: MinGW (“Minimalistic GNU for Windows”)
• MinGW hasn’t implemented threads for Windows yet.
• Standard thread is not working well in windows platform. So need to use ‘Pthread’ for both windows, linux platforms.
• Conversion of code to/fro std:thread and pthread is simple. Hence both having simple identical codes.
• std:thread:
  #include <thread>
  …
  void processFile(long threadid){ //thread function
  //some code
  }
  …
  std::thread threads[NUM_THREADS]; //thread declaration
  threads[threadindex] = std::thread(processFile, threadindex); //thread creation
  usleep(100);
  …
  for(int t=0; t<NUM_THREADS; t++) { //thread must be joined after creation
  threads[t].join();
  }
• pthread:
  #include <pthread.h>
  …
  void processFile(long threadid){ //thread function
  //some code
  pthread_exit(NULL); //thread must be exited here
  }
  …
  pthread_t threads[NUM_THREADS]; //thread declaration
  int rc = pthread_create(&threads[t], NULL, processFile, threadindex);
  //here join not be needed** also in compilation -pthread must be specified
  Ex: g++ -std=c++0x -o bin/main -pthread main.cpp
• If your target platform is Linux only – c++11 std::thread is fine; if you also need Windows or other UNIX – boost::thread is the way to go (OR) can use Pthread

 

4. Directory creation

• //For directory creation we can use the following function:
  void make_directory(const char* name)
  {
  #ifdef __linux__
  mkdir(name, 777);
  #else
  _mkdir(name);
  #endif
  }

 

5. Some more points:

• Can’t calculate the size of pointer array in c++
• delete() of fixed arrays raises segmentation fault in unix, but in windows compilation its working
• To calculate size of the fixed size array:
  lngSize = sizeof(arr_temp) / sizeof(arr_temp[0]);
• Unique function returns address of last element of modified array after duplicates removed.
  To find valid elements in array after duplicated removed:
  noele=unique(arr_temp, arr_temp + arraysize)-arr_temp;  //arr_temp is address of first element