Warning C4244 \ '=': conversion from 'int' to 'char', possible loss of data?

Question

When writing a program for solving a puzzle, I encountered a warning in the following snippet:

std::string str = "hello";

for (int i = 0; i < str.length(); ++i)
    str[i] = toupper(str[i]); //make every letter capital       
//  ^^ warning

I'm getting a warning on the last line above.

Warning C4244 \ '=': conversion from 'int' to 'char', possible loss of data?

Is there any way to get rid of this warning?

Answer 1

Cast the str[i] to a char explicitly like this:

str[i] = (char)toupper(str[i]);

Or:

str[i] = static_cast<char>(toupper(str[i]));

To make the operation more C++ friendly. std::toupper returns an int, which makes the compiler complain. By casting the return value, you tell the compiler you know what you are doing.

As a side note, I recommend using boost::to_upper() on the string at once, like this:

#include <boost/algorithm/string.hpp>
#include <string>

std::string str = "hello";

boost::to_upper(str); //Is HELLO

std::string newstr = boost::to_upper_copy<std::string>("hello"); //is HELLO