c++ copy struct unresolved link

Question

I am working on a date wrapper class in c++

I want to copy the tm structure to another structure, but it throws unresolved external link

Error 2 error LNK2001: unresolved external symbol "public: static struct tm * DateUtils::generateDateTimeStruct" (?generateDateTimeStruct@DateUtils@@2PAUtm@@A)

 class DateUtils
{
public:

    DateUtils()
    {

    }

    static int getTodaysDate();
    static tm * myDateTime;
    static void generateDateTimeStruct();

};

tm* DateUtils::myDateTime = NULL;

int DateUtils::getTodaysDate()
{
   // If i comment the calling, it does not throws an error
    generateDateTimeStruct();
    return DateUtils::myDateTime->tm_hour;
}
static void generateDateTimeStruct(){
        time_t now = time(0);
        static tm s;
        now = time(NULL);
        localtime_s(&s, &now);

        DateUtils::myDateTime = &s;

}

You only declared static member `myDateTime`, you need to define it — billz, Jan 06 '14 at 11:01

LihO · Accepted Answer · 2014-01-06T11:24:08.953

1

You need to define this member outside the class declaration (in some .cpp file):

tm* DateUtils::myDateTime = NULL;

Note that prefixing with the name of the class is used while defining the other members as well:

In the class declaration:

static int getTodaysDate();
static void generateDateTimeStruct();

but the definition outside the class:

int DateUtils::getTodaysDate() { ... }
void DateUtils::generateDateTimeStruct() { ... }

edited Jan 06 '14 at 11:24

answered Jan 06 '14 at 11:03

LihO

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eventhough I have defined it, it still throws the same error – meWantToLearn Jan 06 '14 at 11:12

score 0 · Answer 2 · answered Jan 06 '14 at 11:05

0

As myDateTime has been declared to have static storage, you need to assign some memory to it.

The normal thing to do is to define it in exactly one compilation unit; typically in a source file:

tm* Wrapper::myDateTime = NULL;

answered Jan 06 '14 at 11:05

Bathsheba

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Even with assigning memory to it, it still throws the same error – meWantToLearn Jan 06 '14 at 11:12

score 0 · Answer 3 · answered Jan 06 '14 at 11:05

0

You have to define the static data member. It was only declared in the class definition but not defined outside the class. In some code module write

tm * Wrapper::myDateTime;

answered Jan 06 '14 at 11:05

Vlad from Moscow

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I have done it as-well, but yet same error. – meWantToLearn Jan 06 '14 at 11:06
In the header there must be as before static tm * myDateTime; Outside the header in some code module there must be tm * DateUtils::myDateTime; I do not see where the Wrapper now. – Vlad from Moscow Jan 06 '14 at 11:13
I have updated the code, its throwing link error on DateUtils::generateDateTimeStruct. Its calling a static method from a static method.I just cant get why its not working without any error – meWantToLearn Jan 06 '14 at 11:17
The function must be defined as void DateUtils::generateDateTimeStruct(){ – Vlad from Moscow Jan 06 '14 at 11:21

score 0 · Answer 4 · answered Jan 06 '14 at 11:20

You declare a member function, but define a non-member function with the same name. Change the definition to

static void DateUtils::generateDateTimeStruct(){
    // your code here
}

Alternatively, don't define a class at all - it seems just to be somewhere to put static functions, in which case a namespace would be more appropriate.

c++ copy struct unresolved link

4 Answers4

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