Why does the following code not compile

[SuchtyTV]

#include <iostream>
#include <fstream>
#include <set>
#include <map>
    /*
     * Generates a clause_set and a dictionary, given an inputstream
     * Returns a clause_set
     * Returns a dictionary through the parameter: std::map<std::string, long>
     */
std::set < std::set < long >>generate(std::ifstream &, std::map < std::string,
                                      long >*);

/*
 * Reprints the given Set provided a dictonary.
 */
void printClauseSet(std::set < std::set < long > >, std::map < std::string,
                    long >&);
//Reprints the given Clause
void printClause(std::set < long >, std::map < std::string, long >&);

int main(int argc, char *argv[])
{
  if (argc != 2) {
    std::cout << "You must specify exactly one argument." << std::endl;
    return EXIT_FAILURE;
  }
  std::map < std::string, long >dictonary;
  std::ifstream infile(argv[1]);

  std::set < std::set < long >>clause_set = generate(infile, &dictonary);

}

std::set < std::set < long >>generate(std::fstream & infile,
                                      std::map < std::string, long >*to_return)
{                               //stuffhere}

Compiler Error:

Undefined symbols for architecture x86_64:
"generate(std::__1::basic_ifstream<char, std::__1::char_traits<char> >&, std::__1::map<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, long, std::__1::less<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, std::__1::allocator<std::__1::pair<std::__1::basic _string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const, long> > >*)", referenced from:
_main in main.cpp.o
ld: symbol(s) not found for architecture x86_64

Mysterious to me... What has this to do with x86_64

[laserlight]

It's a link error stating that you didn't define the function named generate which has a first parameter of type std::ifstream&, which is true because you defined an overloaded function named generate that has a first parameter of type std::fstream& instead.

[SuchtyTV]

It's a link error stating that you didn't define the function named generate which has a first parameter of type std::ifstream&, which is true because you defined an overloaded function named generate that has a first parameter of type std::fstream& instead.

Is there anything like casting in C++ ?

In Java you could pass an Object of an Childclass as an object of every upper-class.

[laserlight]

It's the same in C++. You can easily demonstrate this by changing the forward declaration to have an fstream first parameter instead.

As I said, the issue is that you didn't define the function correctly. So, the compiler generated code that invoked the function according to the forward declaration, but the linker couldn't find the function.