问题:

I am running g++(gcc version 3.4.4) on cygwin.

I can't get this small snippet of code to compile. I included the appropriate headers.

int main(){

    std::string temp("asgfsgfafgwwffw");

    std::transform(temp.begin(),
                   temp.end(),
                   temp.begin(),
                   std::toupper);

    std::cout << "result:" << temp << std::endl;

    return 0;
}

I have not had any issues using STL containers such as vector. Does anyone have any suggestions or insights into this situation. Thanks.

回答1:

This explains it quite well.

Which will boil down to this code:

std::transform(temp.begin(),temp.end(),temp.begin(),static_cast<int (*)(int)>(std::toupper));

回答2:

From the link above.

#include <cctype> // for toupper
#include <string>
#include <algorithm>
using namespace std;

void main()
{
string s="hello";
transform(s.begin(), s.end(), s.begin(), toupper);
}
Alas, the program above will not compile because the name 'toupper' is ambiguous. It can refer either to:
int std::toupper(int); // from <cctype>
or
template <class chart> 
  charT std::toupper(charT, const locale&);// from 
  <locale>
Use an explicit cast to resolve the ambiguity:
std::transform(s.begin(), s.end(), s.begin(), 
               (int(*)(int)) toupper);
This will instruct the compiler to choose the right toupper().