function as a function parameter

[itcplpl]

hi,
I have a function xref that takes another function as one of its parameters. however, I get the following error on compilation:

error: too few arguments to function ‘std::map<std::basic_string<char>, std::vector<int> > xref(std::istream&, std::vector<std::basic_string<char> > (*)(const std::string&))’

this is the relevant code:

map<string, vector<int> > xref(istream&, vector<string> (*find_words)(const string&));
vector<string> split(const string&);

int main()
{
  xref(cin);

   return 0;
}

map<string, vector<int> >xref(istream& in, vector<string> find_words(const string&)=split)
{
  string line;
  int line_num=0;
  map<string, vector<int> >ret;

  while(getline(in,line))
    {
      ++line_num;
      vector<string> words=find_words(line);

      for(vector<string>::const_iterator it=words.begin();it!=words.end();++it)
	{
	  ret[*it].push_back(line_num);
	}
    }
  return ret;
}

[helios]

Put the default parameter in the declaration, not in the definition. The compiler performs a single pass, so by the time it finds that the function does in fact take default parameters, it has already reported the error.

[itcplpl]

thanks helios,
i did that, and removed the default parameter from the definition, but now I get the following error:

error: ‘split’ was not declared in this scope

now where do I move the declaration of split to?

[helios]

Of course, you have to move the declaration of split() before the declaration of xref().

[itcplpl]

oops, that was my silly error...thx!

[jloundy]

you are missing the pointer to your function parameter within your definition

map<string, vector<int> >xref(istream& in, vector<string> find_words(const string&))

Should Be

map<string, vector<int> >xref(istream& in, vector<string> (*find_words)(const string&))

[itcplpl]

thx jloundy,
i thought it was not necessary in the definition, but I'll fix it.

[jloundy]

>>i thought it was not necessary in the definition,
I don't see why you could, but I usually typedef a function pointer for syntactical sugar

[itcplpl]

well, I ran it with this code in my main function:

int main()
{
  // xref(cin);

  typedef map<string,vector<int> > msvi;

   msvi rem=xref(cin);

  for (msvi::const_iterator iter=rem.begin();iter!=rem.end();++iter)
     cout<<iter->second.begin()<<endl;

   return 0;
}

and I am getting the following error:

error: no match for ‘operator<<’ in ‘std::cout << iter.std::_Rb_tree_const_iterator<_Tp>::operator-> [with _Tp = std::pair<const std::basic_string<char>, std::vector<int> >, const _Tp* = const std::pair<const std::basic_string<char>, std::vector<int> >*]()->std::pair<const std::basic_string<char>, std::vector<int> >::second.std::vector<_Tp, _Alloc>::begin [with _Tp = int, _Alloc = std::allocator<int>, std::vector<_Tp, _Alloc>::const_iterator = __gnu_cxx::__normal_iterator<const int*, std::vector<int> >, typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::const_pointer = const int*]()’
/usr/include/c++/4.5/ostream:108:7: note: candidates are: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ostream_type& (*)(std::basic_ostream<_CharT, _Traits>::__ostream_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:117:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ios_type& (*)(std::basic_ostream<_CharT, _Traits>::__ios_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>, std::basic_ostream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]
/usr/include/c++/4.5/ostream:127:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:165:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:169:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:173:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/bits/ostream.tcc:91:5: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.5/ostream:180:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/bits/ostream.tcc:105:5: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.5/ostream:191:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:200:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:204:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:209:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:213:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:221:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/ostream:225:7: note:                 std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.5/bits/ostream.tcc:119:5: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>]

[jloundy]

The output stream cannot output iterators

cout<<iter->second.begin()<<endl;

I think you mean this

cout<<iter->second.at(0)<<endl;

[itcplpl]

yes indeed, that's what I meant.
thx jloundy!

[helios]

Alternatively, you could use iter->second.front().

[itcplpl]

cool, thx helios!

[itcplpl]

so, I wanted to revise the code so it read from a file instead of cin, and I revised it to:

int main()
{
  typedef map<string,vector<int> > msvi;
  string pfile="f2.txt";
    ifstream infile;
    infile.open(pfile.c_str());
   
 msvi rem=xref(infile);

      for (msvi::const_iterator iter=rem.begin();iter!=rem.end();++iter)
     {....}
return 0;
}

and the xref function to:

map<string, vector<int> >xref(ifstream& in , vector<string> (*find_words) (const string&))
{
  string line;
  int line_num=0;
  map<string, vector<int> >ret;

  //   std::string pfile="f2.txt";
  //std::ifstream infile;
  //infile.open(pfile.c_str());

  while(getline(in,line))
    {...}
return ret;
}

it compiles alright, but when i run the program, it still expects a cin input...