Ask about function parameters and pass a reference.

**ooosawaddee3** · 11-04-2002

Code:

	CString m_n, m_e, n_str, e_str; 
	int n_strlen, e_strlen;
	UINT k_keyID;

                m_Proc.GetInfo(FileName, n_str, e_str, n_strlen, e_strlen, k_keyID);
	
                m_n = n_str;
                m_e = e_str;

These above is somepart of my code. m_Proc is object and call function GetInfo which have 5 function parameters (FileName, n_str, e_str, n_strlen, e_strlen, k_keyID)

These below is detail of GetInfo function

Code:

void CExtract::GetInfo(const CString& m_FileName, CString n_str, CString e_str, int n_strlen, int e_strlen, UINT keyID)
	{
n_str ="1234";
e_str = "578756";
n_strlen = 4;
e_strlen = 6;
keyID = 48756;
}

but when I see n_str value after exit GetInfo function. I see n_str = {""}
e_str = {""}

I expect n_str = {"1234"} , e_str = {"578756"}

Do you know how to solve my problem?
Thank you for your answer.

**Magos** · 11-04-2002

If you want to modify a variable through an argument, you must use a pointer (<datatype>*) or a reference (<datatype>&). Otherwise, the data will only exist locally in your function.

This will not work as intended, since Var only exists locally in the function:

Code:

void ChangeVariable(int Var)
{
   Var = 12345;
}

int main()
{
   int MyVar = 0;
   ChangeVariable(MyVar);
   cout << MyVar;
   return 0;
}

This on the otherhand will pass the referense of the variable, instead of just its value:

Code:

void ChangeVariable(int& Var)
{
   Var = 12345;
}

int main()
{
   int MyVar = 0;
   ChangeVariable(MyVar);
   cout << MyVar;
   return 0;
}

Or if you prefer to use pointers:

Code:

void ChangeVariable(int* Var)
{
   *Var = 12345;
}

int main()
{
   int MyVar = 0;
   ChangeVariable(&MyVar);
   cout << MyVar;
   return 0;
}

Thread: Ask about function parameters and pass a reference.

Thread Tools

Search Thread

Display

Ask about function parameters and pass a reference.

Similar Threads

Calling a Thread with a Function Pointer.

const at the end of a sub routine?

structure vs class

Interface Question

I need help with passing pointers in function calls