Ubuntu 18.04, gcc version 6.4.0 20180424 (Ubuntu 6.4.0-17ubuntu1)
The following program calling the Eigen library in the Openfoam2.3.1 (a Computational Fluid Dynamics (CFD) class library) build environment, and it is built bt g ++ - 5 compiler.
OpenFOAM 2.3.1 shell environment: source \$HOME/OpenFOAM/OpenFOAM-2.3.1/etc/bashrc $FOAM_SETTINGS; export WM_CC=gcc-5; export WM_CXX=g++-5

Code: Select all

#include <iostream>
#include <Eigen/Dense>
using namespace std;

int main()
{
    cout << "hello CFD" << endl;
    return 0;
}


I got this warning:
./Eigen/src/Core/util/XprHelper.h:438:68: warning: use of old-style cast [-Wold-style-cast]
enum { diag_size = EIGEN_SIZE_MIN_PREFER_DYNAMIC(ExpressionType::RowsAtCompileTime, ExpressionType::ColsAtCompileTime),
^
./Eigen/src/Core/util/Macros.h:376:51: note: in definition of macro ‘EIGEN_SIZE_MIN_PREFER_DYNAMIC’
#define EIGEN_SIZE_MIN_PREFER_DYNAMIC(a,b) (((int)a == 0 || (int)b == 0) ? 0 \
^
./Eigen/src/Core/util/XprHelper.h:438:103: warning: use of old-style cast [-Wold-style-cast]
enum { diag_size = EIGEN_SIZE_MIN_PREFER_DYNAMIC(ExpressionType::RowsAtCompileTime, ExpressionType::ColsAtCompileTime),
^
./Eigen/src/Core/util/Macros.h:376:66: note: in definition of macro ‘EIGEN_SIZE_MIN_PREFER_DYNAMIC’
#define EIGEN_SIZE_MIN_PREFER_DYNAMIC(a,b) (((int)a == 0 || (int)b == 0) ? 0 \
^
./Eigen/src/Core/util/XprHelper.h:438:68: warning: use of old-style cast [-Wold-style-cast]
enum { diag_size = EIGEN_SIZE_MIN_PREFER_DYNAMIC(ExpressionType::RowsAtCompileTime, ExpressionType::ColsAtCompileTime),
^
when I use g++ to compile this programm, I will not get this warning.

can you help me?