错误信息：非标准语法； 使用“&”创建指向成员的指针

Question

I want to try the test code from the OptimLib page (link)

OptimLib

This is the code from the optimlib page:

i just changed the code a little bit. The following function is now a normal function that you can call instead of the original "main" function

void optimizationApp::optimTest()
{

// initial values:
arma::vec x = arma::ones(2,1) + 1.0; // (2,2)

//

std::chrono::time_point<std::chrono::system_clock> start = std::chrono::system_clock::now();

bool success = optim::de(x,ackley_fn,nullptr);

std::chrono::time_point<std::chrono::system_clock> end = std::chrono::system_clock::now();
std::chrono::duration<double> elapsed_seconds = end-start;

if (success) {
    std::cout << "de: Ackley test completed successfully.\n"
              << "elapsed time: " << elapsed_seconds.count() << "s\n";
} else {
    std::cout << "de: Ackley test completed unsuccessfully." << std::endl;
}

arma::cout << "\nde: solution to Ackley test:\n" << x << arma::endl;

}

The following function is the optimization function:

double optimizationApp::ackley_fn(const arma::vec& vals_inp, arma::vec* grad_out, void* opt_data)
{
const double x = vals_inp(0);
const double y = vals_inp(1);
const double pi = arma::datum::pi;

double obj_val = -20*std::exp( -0.2*std::sqrt(0.5*(x*x + y*y)) ) - std::exp( 0.5*(std::cos(2*pi*x) + std::cos(2*pi*y)) ) + 22.718282L;

//

return obj_val;
}

But when i want to compile the code, the error message appears in this line:

bool success = optim::de(x,ackley_fn,nullptr);

error: reference to non-static member function must be called optimizationApp::ackley_fn': non-standard syntax; use '&' to create a pointer to member

The two test function i use, are defined in the header of my software

        void optimTest();
        double ackley_fn(const arma::vec& vals_inp, arma::vec* grad_out, void* opt_data);

What did i wrong, has anybody an idea? I don't know how to fix the error.

I would be pleased, if someone can give me a tip

Best wishes and stay healthy during the pandemic

Answer 1

I created a new project and copied the code 1 to 1 into it. In the Pro file (I use Qt and MSVC2015x64) I added Armadillo and the OptimLib.

QT -= gui

CONFIG += c++11 console
CONFIG -= app_bundle

DEFINES += QT_DEPRECATED_WARNINGS


SOURCES += \
    main.cpp

 INCLUDEPATH +=  optimlib \                             
            armadillo-7.800.1/include

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

Now comes the following error:

error: C2039: 'function': is not a member of 'std'

I then included "functional" and the error was gone. As a result, there are now errors in functional itself.

I do not understand why ? I had built the Header Only Library in Linux and copied it to my Windows system, but they are only ".hpp" files. So this should work independently of a compiler or ? The Armadillo Library I use is also header only and is located in the workspace of my program, like OptimLIb

How do I get the library to run? Or does the library not work at all under my conditions ?

Answer 2

Put your libraries in your workspace. Do not change anything on the libraries themselves. Include them in your software. Before you include the optimlib, include the default libraries that are missing.

#include <functional>
#include <chrono>
....
#include "armadillo"
#include "optim"

That should be it.