In what library or header file is the "getline()" function declared in?

Question

I am new to c++ programming, and based on what I learned we import the basic input and output functions from the <iostream> library. However, when I use the getline() function, which is used to take user's input with spaces: getline(cin, variable), the program works without including any other library, and I havent seen getline() in any references for the <iostream> header file.

Shouldn't there be a header file that we should include? Or, is it declared in <iostream> ?

I searched online but couldn't find any explanation to this.

• Peter: You could have readily found an answer to this question for yourself by searching for "C++ getline" after finding that documentation for <iostream> have no mention of std::getline(). With such a search, you would have easily turned up the information that Remy provided in his answer.

Answer 1

Shouldn't there be a header file that we should include?

Yes - std::getline() is defined in the <string> header. See the documentation at cppreference.com:

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Or, is it declared in <iostream> ?

Standard headers are allowed to include other standard headers, so in your particular compiler implementation, the <iostream> header is likely already including <string> for you, which is why your code compiles without needing #include <string> in your own code.

But, this is not guaranteed behavior, so you should not rely on it. Always explicitly #include any relevant header that your code needs. If a header has already been included earlier, your include of that header will simply be ignored as a no-op due to use of header guards.

• Mohamad Khalil: "Standard headers are allowed to include each other," what do you exactly mean by this?
• Eljay: @MohamadKhalil • it means the <iostream> header file could have a #include <string> preprocessor directive in it. Or it may not. You don't know.
• Mohamad Khalil: So what could be the reason if it didn't have #include <string> ?
• David C. Rankin: A good reference always helps, look at the 1st line under the title std::getline - cppreference.com