identifier "string" undefined?

Question

I am receiving the error: identifier "string" undefined.

However, I am including string.h and in my main file, everything is working fine.

CODE:

#pragma once
#include <iostream>
#include <time.h>
#include <string.h>

class difficulty
{
private:
    int lives;
    string level;
public:
    difficulty(void);
    ~difficulty(void);

    void setLives(int newLives);
    int getLives();

    void setLevel(string newLevel);
    string getLevel();
};

Can someone please explain to me why this is occurring?

As a side comment, you should use include guards in your code. If your compiler does better with the #pragma once directive, combine the two: #ifndef XXX_HEADER // #define XXX_HEADER // #pragma once // ... // #endif where the order is important (i.e. include guard enclosing the pragma) — David Rodríguez - dribeas
– David Rodríguez - dribeas, Commented Aug 22, 2011 at 12:00

Puppy · Accepted Answer · 2011-08-22 11:23:34Z

134

<string.h> is the old C header. C++ provides <string>, and then it should be referred to as std::string.

answered Aug 22, 2011 at 11:23

Puppy

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1 Comment

Puppy Over a year ago

Don't using namespace std, I've already downvoted all the answers that recommend that for a reason.

Jeankowkow · Accepted Answer · 2019-11-26 18:15:37Z

31

You want to do #include <string> instead of string.h and then the type string lives in the std namespace, so you will need to use std::string to refer to it.

edited Nov 26, 2019 at 18:15

Jeankowkow

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answered Aug 22, 2011 at 11:23

Flexo - Save the data dump♦

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Comments

m0skit0 · Accepted Answer · 2011-08-22 11:24:32Z

12

You forgot the namespace you're referring to. Add

using namespace std;

to avoid std::string all the time.

answered Aug 22, 2011 at 11:24

m0skit0

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5 Comments

m0skit0 Over a year ago

For those who downvoted: thanks for your constructive comments :P

Puppy Over a year ago

using namespace std; is really bad, especially in a header.

m0skit0 Over a year ago

Thanks! Can you please explain why?

Puppy Over a year ago

There's an SO question about it, I believe.

m0skit0 Over a year ago

Here (if someone wants to know)

Ernest Friedman-Hill · Accepted Answer · 2011-08-22 11:23:34Z

11

Because string is defined in the namespace std. Replace string with std::string, or add

using std::string;

below your include lines.

It probably works in main.cpp because some other header has this using line in it (or something similar).

answered Aug 22, 2011 at 11:23

Ernest Friedman-Hill

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Comments

Pierre Lacave · Accepted Answer · 2014-06-10 16:54:34Z

7

#include <string> would be the correct c++ include, also you need to specify the namespace with std::string or more generally with using namespace std;

edited Jun 10, 2014 at 16:54

answered Aug 22, 2011 at 11:24

Pierre Lacave

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Nicol Bolas · Accepted Answer · 2011-08-22 11:24:04Z

5

Perhaps you wanted to #include<string>, not <string.h>. std::string also needs a namespace qualification, or an explicit using directive.

answered Aug 22, 2011 at 11:24

Nicol Bolas

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Camelot · Accepted Answer · 2011-08-22 11:25:36Z

5

You must use std namespace. If this code in main.cpp you should write

using namespace std;

If this declaration is in header, then you shouldn't include namespace and just write

std::string level;

answered Aug 22, 2011 at 11:25

Camelot

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