cquery没有调用'to_upper'的匹配功能

Question

#include <iostream>
#include <string>
#include <boost/algorithm/string.hpp>
using namespace std;

int main() {
  string city1, city2;
  cout << ("Please enter your citys name");
  cin >> city1;
  cout << ("Please enter your citys second name");
  cin >> city2;
  cout << city1 [0,1,2,3,4];
  cout << city2 [0,1,2,3,4];
  boost::to_upper(city1, city2);
  cout << city1,city2;
}

这是我的代码，出于某种原因 boost::to_upper(city1, city2); 得到错误：[cquery] 没有匹配的函数调用 'to_upper'

Answer 1

boost::algorithm::to_upper声明为（来自boost 参考）

template<typename WritableRangeT> 
void to_upper(WritableRangeT & Input, const std::locale & Loc = std::locale());

所以你只能向这个函数传递一个字符串。 更换

boost::to_upper(city1, city2);

和

boost::to_upper(city1);
boost::to_upper(city2);

使代码编译，示例输出是Please enter your citys namePlease enter your citys second nameosLONDON 。 它缺少换行符，还有一个错误 - 对逗号运算符的误解。 通常逗号用于分隔参数或数组元素，但在行中

cout << city1 [0,1,2,3,4];
cout << city2 [0,1,2,3,4];
// ...
cout << city1,city2;

使用逗号运算符。 逗号运算符有两个操作数，它的值是右操作数的值（例如在int x = (1, 2);变量x等于 2）。 上面的代码等价于

cout << city1[4];
cout << city2[4];
// ...
cout << city1;
city2;

最后，更正后的代码是

#include <iostream>
#include <string>
#include <boost/algorithm/string.hpp>
using namespace std;

int main() {
  string city1, city2;
  cout << "Please enter your citys name" << std::endl;
  cin >> city1;
  cout << "Please enter your citys second name" << std::endl;
  cin >> city2;
  cout << city1 << std::endl;
  cout << city2  << std::endl;
  boost::to_upper(city1);
  boost::to_upper(city2);
  cout << city1 << std::endl << city2 << std::endl;
}