What causes the following linking error with the boost c++ libraries?

Question

Hi I get a linking error when compiling my program with the gcc compiler on cygwin. The first picture is a simple sample program from the boost filesystem libraries tutorial page where I have included filesystem.hpp in the boost folder. Beneath that is the picture of my linker error when I try to compile with the following command:

g++ -I C:/Users/Ejer/Desktop/c++Dep/boost_1_77_0 -I C:/Users/Ejer/Desktop/c++Dep/eigen-3.4.0 -L C:/Users/Ejer/Desktop/c++Dep/boost_1_77_0/stage/lib test.cpp -o ser

Here I try to compile my program test.cpp with the eigen and boost libraries and set the includer path that they tell me to set as the path after I have built the library with b2.exe. I have also linked to the lib files for boost. I have also tried linking to the different filesystem lib files specifically. Thanks in advance

#include <iostream>
#include <boost/filesystem.hpp>
using std::cout;
using namespace boost::filesystem;

int main(int argc, char* argv[])
{
  if (argc < 2)
  {
    cout << "Usage: tut3 path\n";
    return 1;
  }

  path p (argv[1]);

  try
  {
    if (exists(p))
    {
      if (is_regular_file(p))
        cout << p << " size is " << file_size(p) << '\n';

      else if (is_directory(p))
      {
        cout << p << " is a directory containing:\n";

        for (directory_entry& x : directory_iterator(p))
          cout << "    " << x.path() << '\n';
      }
      else
        cout << p << " exists, but is not a regular file or directory\n";
    }
    else
      cout << p << " does not exist\n";
  }

  catch (const filesystem_error& ex)
  {
    cout << ex.what() << '\n';
  }

  return 0;
}

Answer 1

I get a linking error when compiling my program

No, you don't. You are getting a linking error when linking your program, not when compiling it.

The reason: you didn't supply the library (-L C:/Users/.... tells the linker where to search for libraries; not which libraries to link). Your command line should look something like:

g++ -I ... -L ... test1.cpp -o ser -lboost_filesystem