C++ Pass A String

You can write your function to take a const std::string&:

void print(const std::string& input)
{
    cout << input << endl;
}

or a const char*:

void print(const char* input)
{
    cout << input << endl;
}

Both ways allow you to call it like this:

print("Hello World!\n"); // A temporary is made
std::string someString = //...
print(someString); // No temporary is made

The second version does require c_str() to be called for std::strings:

print("Hello World!\n"); // No temporary is made
std::string someString = //...
print(someString.c_str()); // No temporary is made

You should be able to call print("yo!") since there is a constructor for std::string which takes a const char*. These single argument constructors define implicit conversions from their aguments to their class type (unless the constructor is declared explicit which is not the case for std::string). Have you actually tried to compile this code?

void print(std::string input)
{
    cout << input << endl;
} 
int main()
{
    print("yo");
}

It compiles fine for me in GCC. However, if you declared print like this void print(std::string& input) then it would fail to compile since you can't bind a non-const reference to a temporary (the string would be a temporary constructed from "yo")

Well, std::string is a class, const char * is a pointer. Those are two different things. It's easy to get from string to a pointer (since it typically contains one that it can just return), but for the other way, you need to create an object of type std::string.

My recommendation: Functions that take constant strings and don't modify them should always take const char * as an argument. That way, they will always work - with string literals as well as with std::string (via an implicit c_str()).