C++ “no match for operator=“ error in lambda function

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• C++ Linked List, bad_alloc

  My teacher gave us the main.cpp (mostly just data to test the program) and a header file for a Linked List. I'm pretty sure I have most of it okay, but having issues turning into a vector with the method/parameters he gave us:

  vector<string> LinkedList::toVector(bool sorted) const
  {
      vector<string> result;
  
      Node *current = mFront->mNext;
      while (current != mRear)
      {
          result.push_back(string(current->mData));
          current = current->mNext;
      }
  
      if (sorted)
      {
          sort(result.begin(), result.end());
      }
      return result;
  }
  

  I keep getting an error saying that there is bad memory allocation on the push_back line. Any advice?

  Edit: I didn't put enough of the code in

  The Node class was created in the private access modifier of linkedList.h - code for that is:

  private:
  
      class Node
      {
          friend class LinkedList;
  
      public:
          inline Node *getNext() const
          {
              return mNext;
          };
  
          inline string getData()
          {
              return mData;
          }
  
      private:
          inline Node(string data)
          {
              mPrevious = mNext = 0;
              mData = data;
          }
  
          string mData;
          Node *mPrevious;
          Node *mNext;
      };
  

  I attempted debugging and that was actually how I found out exactly what line the exception was being thrown from. I'm not sure how to test whether it is push_back that is the issue or whether the string is throwing, as someone suggested.

  current->mData should be giving back a string as long as I'm looking at it right, that's what the main.cpp is using to populate everything.
• LAPACK matrix inversion: unable to program

  I am developing embedded software on ARM Cortex-A53 (armv7/v8) for image processing, and I need some help for a specific algorithm.

  This later involves complex (real/imaginary parts) matrix inversion with large size (up to 24x24). The most significant constraint is the timing execution.

  I am currently looking for a library, optimized for ARM (using NEON SIMD?), which offers this kind of operation (matrix inversion of large size, with complex numbers).

  I did try Eigen library: it works fine, but it is too slow. Our processor runs at 1 GHz, and I got an average duration of 0,82 ms for a complex double matrix inversion of size 24x24.

  I also had a look at:

  • Ne10 library: it does not propose matrix inversion with complex number (no template used) and large size (maximum size is 4x4).
  • ARM Compute Library: cannot find matrix inversion function. I am not sure it is implemented.
  • ARM Performance Libraroes: I am still looking for the matrix inversion, does anyone knows which function/class I should have a look to?

  Please, any C++ libraries (should be templated for use of complex), optimized for ARM, could you suggest?

  Thanking you in advance!

  Laurent.

  UPDATE

  I am currently testing the C LAPACK (=LAPACKE) library to complete a matrix inversion.

  I do have problem to link my code. Look at C++ code (example of code got from internet, very simple):

  #include "test_lapacke.hh"
  
  
  extern "C"
  {
  #include <lapacke.h>
  }
  
  
  lapack_int matInv(double *A, unsigned n)
  {
      int ipiv[n+1];
      lapack_int ret;
  
      ret =  LAPACKE_dgetrf(LAPACK_COL_MAJOR,
                            n,
                            n,
                            A,
                            n,
                            ipiv);
  
      if (ret !=0)
          return ret;
  
  
      ret = LAPACKE_dgetri(LAPACK_COL_MAJOR,
                         n,
                         A,
                         n,
                         ipiv);
      return ret;
  }
  
  /**********************************************************************************************************************/
  void Test_lapacke()
  {
      double A[] = {
          0.378589,   0.971711,   0.016087,   0.037668,   0.312398,
          0.756377,   0.345708,   0.922947,   0.846671,   0.856103,
          0.732510,   0.108942,   0.476969,   0.398254,   0.507045,
          0.162608,   0.227770,   0.533074,   0.807075,   0.180335,
          0.517006,   0.315992,   0.914848,   0.460825,   0.731980
      };
  
      for (int i=0; i<25; i++) {
          if ((i%5) == 0) putchar('\n');
          printf("%+12.8f ",A[i]);
      }
      putchar('\n');
  
      matInv(A,5);
  
      for (int i=0; i<25; i++) {
          if ((i%5) == 0) putchar('\n');
          printf("%+12.8f ",A[i]);
      }
      putchar('\n');
  }
  

  I did add all blas/lapack libraries to C++ linker on my project: -llapack -llapacke -lrefblas -lcblas -ltmglib

  But I still got the error:

  /path/lib/liblapacke.a(lapacke_dgetrf_work.o): In function LAPACKE_dgetrf_work': lapacke_dgetrf_work.c:(.text+0xd8): undefined reference todgetrf_' lapacke_dgetrf_work.c:(.text+0x160): undefined reference to dgetrf_' /path/lib/liblapacke.a(lapacke_dgetri_work.o): In functionLAPACKE_dgetri_work': lapacke_dgetri_work.c:(.text+0xe4): undefined reference to dgetri_' lapacke_dgetri_work.c:(.text+0x174): undefined reference todgetri_' collect2: error: ld returned 1 exit status make: *** [Test_matrice] Erreur 1

  Any ideas to solve this?

  Many thanks! Regards, Laurent.
• Understanding delete in C++ with

  I have following code snippet from a C++ book I am reading.

  int* operator=(const int& rhs, int *x)
  {
     int *tmpx=x              //line 1
     x = new int(2)           //line 2 
     delete tmpx;             //line 3
     return x;                //line 4                   
  }
  

  My doubt is that If I am deleting tmpx on line 3 which holds the address to memory location that x points to, and deleting will invalidate the memory address, So wouldn't it be wrong to return x which is pointing to memory address that was freed at line 3 ?
• Lambdas assigned to variables in Kotlin. Why?

  I noticed that I get the same effect if I define this trivial function:

  fun double ( i: Int ) = i*2
  

  and if I define a variable and assign a lambda (with an identical body) to it:

  var double = { i : Int -> i*2 }
  

  I get the same result if I call double(a) with either declaration. This leaves me confused. When is it needed, recommended, advantageous to define a variable as a lambda rather than define a function to it?
• C++ perfect forwarding in nested lambda

  I have a case where I am constructing a special thread object. This object must take a callable in the same way the std::thread does, do some validation, and then wrap it in another function which does some additional things (exact rationale is complicated and not relevant to this question). I have a working solution but I am not convinced that it is optimal as I have not managed to get perfect forwarding working.

  I created the following example to debug the issue and try to understand what my error is.

  The example compiles and runs without issue. However googletest's address sanitizer gives me this error:

  AddressSanitizer: stack-use-after-scope on address 0x7ffcea0a8ff0 at pc 0x00000052a019 bp 0x7fee283febb0 sp 0x7fee283feba8

  In the example I have a function called safe_function_executer. In this safe function the outermost lambda captures the function and arguments by value. I also have a function called bad_function_executer in which I attempt perfect forwarding by capturing the function and arguments by reference.

  Googletest's address sanitizer does not throw an error for the safe_function_executer but it does for the bad_function_excecuter.

  I am having difficulty understanding where I am accessing a value that has gone out of scope in this example. Does anyone know why Googletest's address sanitizer would be throwing this error?

  #include <atomic>
  #include <thread>
  #include <array>
  #include <functional>
  #include <iostream>
  #include <chrono>
  
  //!!!WARNING Contrived Example Follows!!!
  
  template<class SomeType, class F, class ...Args>
  void a_function_running_function( SomeType& some_arg, F&& f, Args&&... args)
  {
      f(std::forward<Args>(args)...);
      *some_arg = 42;
  }
  
  template<class SomeType, class F, class ...Args>
  std::thread safe_function_executer( SomeType& some_arg, F&& f, Args&&... args )
  {
      return std::thread( [=]() mutable { 
          a_function_running_function( some_arg, [&]() mutable {
              f( std::forward<Args>(args)... ); });});
  
  }   
  
  
  template<class SomeType, class F, class ...Args>
  std::thread bad_function_executer( SomeType& some_arg, F&& f, Args&&... args )
  {
      return std::thread( [&,some_arg]() mutable { 
          a_function_running_function( some_arg, [&]() mutable {
              f( std::forward<Args>(args)... ); });});
  
  }
  
  void some_function(int arg1, bool arg2, std::tuple<int,bool>& ret)
  {
      std::get<0>(ret) = arg1;
      std::get<1>(ret) = arg2;
  }
  
  int main()
  {
      auto arg = std::make_shared<std::atomic<int>>(0);
      auto ret = std::tuple<int,bool>{0, false};
  
      //works (but not perfectly forwarded?)
      auto good_thread = safe_function_executer( arg, &some_function,
                                                 45, true, ret ); 
      good_thread.join();
  
      //address sanitizer errors
      auto bad_thread = bad_function_executer( arg, &some_function,
                                               45, true, ret );
      bad_thread.join();
  }
  
• Java Lambdas Interfaces

  As you all know we engineers works best at nights :) I was studying lambdas at yesterday night and I saw a piece of code like that,

      BirdCompare tester = new BirdCompare();
      MathOperation addition = (a, b) -> (a + b);
      MathOperation subtraction = (int a, int b) -> (a - b);
      MathOperation multiplication = (int a, int b) -> {
          return a * b;
      };
      MathOperation division = (a, b) -> a / b;
  
      interface MathOperation {
          int operation(int a, int b);
      }
  

  The sample simply assigned lambda expression to MathOperation interface's variable but how ? It makes a implementation of method named operation which is in the interface and the point I was confused is assignment of that implementation to the variable of interface. I really wonder the idea based on this approach. Thank you in advance to all.
• Error in NVCC: <command-line>:0:1: error: macro names must be identifiers

  I am on Ubuntu 18.04, gcc 7, CUDA 10. The below compiles without warnings

  g++ main.cpp -DDISABLE_WINDOWS_WARNING="__pragma(warning(push,0))"
  

  However if I simply switch g++ to nvcc like the below

  nvcc main.cu -DDISABLE_WINDOWS_WARNING="__pragma(warning(push,0))"
  

  The below error shows up:

  <command-line>:0:1: error: macro names must be identifiers
  

  Both main.cpp and main.cu can be minimal and is not the reason of this error.

  Is this a bug in NVCC?
• Compiling python 3.7 on Solaris 11.2 fails at link stage

  I am trying to compile python 3.7 on solaris 11.2. The compiling seems to be error free until the linking phase. I do not have root access.

  I have tried the following:

    ./configure --prefix=/appgroup/appuser
    make
  
    ./configure --prefix=/appgroup/appuser --enable-shared
    make
  

  Both error out with:

  gcc    -o python Programs/python.o -Wl,-R,/appgroup/appuser/scripts/lib -L. -lpython3.7m -lsocket -lnsl -lintl -ldl -lsendfile   -lm  
  Undefined                       first referenced
   symbol                             in file
  libintl_bind_textdomain_codeset     ./libpython3.7m.so
  libintl_gettext                     ./libpython3.7m.so
  libintl_textdomain                  ./libpython3.7m.so
  libintl_dcgettext                   ./libpython3.7m.so
  libintl_bindtextdomain              ./libpython3.7m.so
  libintl_dgettext                    ./libpython3.7m.so
  ld: fatal: symbol referencing errors
  collect2: error: ld returned 1 exit status
  *** Error code 1
  make: Fatal error: Command failed for target `python'
  

  I think the error is based on the conflict between /usr/include/libintl.h and /usr/local/include/libintl.h, because the one in /usr/local/include had those variables, while /usr/include does not.

  I tried to set CFLAGS="-I/usr/include -I/usr/local/include" and CFLAGS="-I/usr/local/include -I/usr/include", but the result was the same.

  Any ideas?
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  I am trying to create a brand new Swift project in Xcode 10. But it is giving me build errors. This is the exact error that I get:

  < unknown >:0: error: Swift does not support the SDK 'iPhoneSimulator11.2.sdk' Command CompileSwiftSources failed with a nonzero exit code