Why do we need to include the header file when std::string will suffice to initialize a string in C++?

Question

#include <iostream>

int main() {

    std::string a="hello";
    std::cout<< a;
}

The above code prints out "hello". Then, why do people insist upon including the <string> header file?

type "using namespace std;" before int main() . you dont need to type std::something again and again .. — Ankur Jyoti Phukan, Dec 20 '15 at 16:24
@AnkurJyotiPhukan That is considered bad practice in serious programs. Its okay for small homework style questions: https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice — Galik, Dec 20 '15 at 16:27
@AnkurJyotiPhukan That is not exactly a good advice. While it might be easier to type, it's not recommended to plop the entire std namespace in a global one. — Franko Leon Tokalić, Dec 20 '15 at 16:27
[Which headers in the C++ standard library are guaranteed to include another header?](http://stackoverflow.com/q/26614983/3953764) — Piotr Skotnicki, Dec 20 '15 at 16:37

score 9 · Accepted Answer · answered Dec 20 '15 at 16:16

9

There is no guarantee your code will work without <string>. That is the header std::string is defined in, so you must include it if you want your code to be portable.

Your code may work or appear to work because <iostream> directly or indirectly includes <string>.

answered Dec 20 '15 at 16:16

juanchopanza

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In at least some implementations, `` includes `basic_string` and its aliaces, but not additional string facilities, like `to_string` and `stoi`. Other implementation includes `basic_string`, but not its aliases, so declaring `basic_string` will work, but `std::string` won't. – Revolver_Ocelot Dec 20 '15 at 16:29
@Revolver_Ocelot: Wouldn't a forward-declaration for `std::basic_string` suffice for implementing that header? – Deduplicator Dec 27 '15 at 18:57

Soner from The Ottoman Empire · Answer 2 · 2015-12-20T16:33:33.417

3

I think your compiler is just being nice to you. If you are using strings, you should #include <string>, whether or not your particular compiler lets you get away without it. Moreover, apparently <iostream> includes <string>, directly or indirectly, but don't rely on it.

edited Dec 20 '15 at 16:33

answered Dec 20 '15 at 16:21

Soner from The Ottoman Empire

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"not supposed to ... `#include `" - not so. Standard headers are allowed to include any other standard headers. – Pete Becker Dec 20 '15 at 16:31
yes you are right @PeteBecker – Soner from The Ottoman Empire Dec 20 '15 at 16:33

Why do we need to include the header file when std::string will suffice to initialize a string in C++?

2 Answers2