Why would we want to do this:

#include <iostream>

void print(std::ostream& os) {
  os << "Hi";
}

int main() {
  print(std::cout);
  return 0;
}

instead of this:

#include <iostream>

void print() {
  std::cout << "Hi";
}

int main() {
  print();
  return 0;
}

Is there some certain advantage or functionality that is obtained only with the first version?

CodePudding user response：

Yes, the first version is significantly better. Like already mentioned in the comments, it allows you to use any kind of std::ostream, not just std::cout. Some of the most important consequences of this architectural choice are:

1. You can use your function to print the required data to standard output, a file, a custom class written by your colleagues (e.g. database adapter, logger).

2. It is possible to test your void print function. E.g.:

TEST(MyFunctionShould, printHello)
{
  std::string expectedResult("Hello");
  std::ostringstream oss;
  print(oss);
  ASSERT_EQ(expectedResult, oss.str());
}