在C中将最低效率转换为大写的最有效方法是什么？

#include <iostream>
#include <string>

int main() {
    std::string str = "hello world";
    std::string uppercaseStr = std::to_uppercase(str);
    std::cout << uppercaseStr << std::endl;
    return 0;
}

HELLO WORLD

#include <iostream>
#include <string>

int main() {
    std::string str = "hello world";
    std::string uppercaseStr = std::uppercase(str);
    std::cout << uppercaseStr << std::endl;
    return 0;
}

HELLO WORLD