Question

is there a single function in c++ that converts strings from lowercase to uppercase and vice versa? I need to compare two strings case insensitive and I can only convert one of the strings and the other needs to be intact.

Answer 1

You can use std::toupper or std::tolower, in combination with std::for_each std::transform.

#include <cctype>
#include <algorithm>
#include <string>
#include <iostream>

int main()
{
  std::string s = "Hello, World!";
  std::transform(s.begin(), s.end(), s.begin(), [](char c) {return std::toupper(c);});
  std::cout << s << "\n";
}

Edit

I need to compare two strings case insensitive and I can only convert one of the strings and the other needs to be intact.

You can define a function that performs a case-insensitive comparison of two characters, then use it with std::equal:

bool case_insensitive_comp(char lhs, char rhs)
{
  return std::toupper(lhs) == std::toupper(rhs);
}

int main()
{
  std::string s1 = ....;
  std::string s2 = ....;
  bool match = std::equal(s1.begin(), s1.end(), s2.begin(), case_insensitive_comp); 
}

You might have to check that the length of the strings is the same before the call to std::equal.