C++ toupper symbol clash?

[Jonny Grant]

Hello

I thought functions can have the same name, because params are different 
in C++

eg my
void tolower(std::string & str)

But I get a build error. I had expected not to conflict

I'm not on this list, so please cc me in any replies.
Thank you, Jonny

int toupper( int ch );
http://en.cppreference.com/w/cpp/string/byte/toupper


$ g++ -O2 -Wall -Wextra -Wpedantic -o main main.cpp
main.cpp: In function ‘void tolower(std::__cxx11::string&)’:
main.cpp:23:66: error: no matching function for call to 
‘transform(std::__cxx11::basic_string<char>::iterator, 
std::__cxx11::basic_string<char>::iterator, 
std::__cxx11::basic_string<char>::iterator, <unresolved overloaded 
function type>)’
      std::transform(str.begin(), str.end(), str.begin(), ::tolower);
                                                                   ^
In file included from /usr/include/c++/5/algorithm:62:0,
                  from main.cpp:3:
/usr/include/c++/5/bits/stl_algo.h:4164:5: note: candidate: 
template<class _IIter, class _OIter, class _UnaryOperation> _OIter 
std::transform(_IIter, _IIter, _OIter, _UnaryOperation)
      transform(_InputIterator __first, _InputIterator __last,
      ^
/usr/include/c++/5/bits/stl_algo.h:4164:5: note:   template argument 
deduction/substitution failed:
main.cpp:23:66: note:   couldn't deduce template parameter ‘_UnaryOperation’
      std::transform(str.begin(), str.end(), str.begin(), ::tolower);
                                                                   ^
In file included from /usr/include/c++/5/algorithm:62:0,
                  from main.cpp:3:
/usr/include/c++/5/bits/stl_algo.h:4201:5: note: candidate: 
template<class _IIter1, class _IIter2, class _OIter, class 
_BinaryOperation> _OIter std::transform(_IIter1, _IIter1, _IIter2, 
_OIter, _BinaryOperation)
      transform(_InputIterator1 __first1, _InputIterator1 __last1,
      ^
/usr/include/c++/5/bits/stl_algo.h:4201:5: note:   template argument 
deduction/substitution failed:
main.cpp:23:66: note:   candidate expects 5 arguments, 4 provided
      std::transform(str.begin(), str.end(), str.begin(), ::tolower);





//g++ -O2 -Wall -Wextra -Wpedantic -o main main.cpp

#include <algorithm>
#include <string>
#include <iostream>

void myfunc(int i)
{
     i = 10;

     std::cout << i;
}

void myfunc(std::string i)
{
     i = "10";

     std::cout << i;
}

void tolower(std::string & str)
{
     std::transform(str.begin(), str.end(), str.begin(), ::tolower);
}

int main (void)
{
     std::string caps = "FOO";

     tolower(caps);

     return 0;
}