C++ can't create vector

Question

This is weird. I created a vector just fine in one class but can't create it in another class. He's a representation of what I have:

main.h

#include <Windows.h>
#include <ShellAPI.h>
#include <vector>
#include <string>
#include <iostream>

#include "taco.h"

class MyClass
{

public:
    int someint;
    vector<int> myOrder;
};

taco.h

#include <vector>

class OtherClass
{

public:
    vector<int> otherOrder;
};

And I get compile errors regarding the vector declaration in taco.h:

error C2143: syntax error : missing ';' before '<'
error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
error C2238: unexpected token(s) preceding ';'

What am I missing here? I can uncomment out that second vector declaration and it compiles fine.

This suggests to me that some .h file has `using namespace std;` in it somewhere, which is generally a Bad Idea. `using` should never be done in headers, as it messes up namespaces for any .cpp file that directly or indirectly includes that header. Leave `using` for the source files only, where the effects are local. — David Thornley, Jul 28 '10 at 18:09

score 13 · Accepted Answer · edited May 23 '17 at 12:01

13

Try:

std::vector<int> otherOrder;

vector is part of the std namespace. This means that whenever you use a vector in a header file, you should include the std:: prefix.

The reason that you can sometimes get away with forgetting it is that some included files may have using namespace std; in them, allowing you to leave off the prefix. However, you should avoid the using keyword in header files, for it will pollute the namespace of any files that include it.

For a more detailed explanation of the dangers of using namespace ..., see this thread.

edited May 23 '17 at 12:01

Community

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answered Jul 28 '10 at 17:58

Justin Ardini

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[This answer](http://stackoverflow.com/questions/2879555/c-stl-how-to-write-wrappers-for-cout-cerr-cin-and-endl/2880136#2880136) is another argument against `using namespace std`. – sbi Jul 28 '10 at 18:10
Hmmm for some reason I thought my "using namespace std" in main.h would cascade down to taco.h. Thanks for the answer! – Jake Wilson Jul 28 '10 at 18:17
@Jakobud: If you had the reverse (`using namespace std;` in `taco.h` but not `main.h`), it would. The only way for it to "cascade" is through `#include`. – Justin Ardini Jul 28 '10 at 18:18

score 4 · Answer 2 · answered Jul 28 '10 at 17:58

4

Try std::vector<int>. You're supposed to use the namespace --- I'm assuming you have

using namespace std;

in the main.h someplace. There's a lot of talk on SO as to why using using is bad practice ; I'd recommend that you check it out.

answered Jul 28 '10 at 17:58

Jacob

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score 4 · Answer 3 · answered Jul 28 '10 at 17:58

4

All C++ standard library objects live in the std namespace. Try

class MyClass
{

public:
    int someint;
    std::vector<int> myOrder;
//  ^^^^^
};

answered Jul 28 '10 at 17:58

kennytm

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score 1 · Answer 4 · answered Jul 28 '10 at 17:59

1

std::vector<int> ?

answered Jul 28 '10 at 17:59

a1ex07

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C++ can't create vector

4 Answers4