Re: C++ toupper symbol clash?

[Xi Ruoyao <ryxi at stu dot xidian dot edu dot cn>]

On 2017-08-05 03:02 +0100, Jonny Grant wrote:
> Hello
> 
> I thought functions can have the same name, because params are different 
> in C++

Yes they can.

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

Yes it's correct.

> 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;
> }

This won't work.  Reduced version:

  int foo(int i);
  char foo(char i);

  template <typename T, typename Func>
  void bar(T t, Func func);

  int main (void)
  {
      bar('c', foo); // BOOM!
      return 0;
  }

It's impossible to deduce which type ‘Func’ should be at the
line with "BOOM!".  Should it be char(*)(char) or int(*)(int)?
Note that we don't have the definition of 'bar', and don't know
how 'bar' would use 'func' so both are possible.
-- 
Xi Ruoyao <ryxi@stu.xidian.edu.cn>
School of Aerospace Science and Technology, Xidian University