MFC，如何在CArray中获取元素，该元素类型为CString

Question

I am confuse in GetAT and aryString[n], as follow code

CArray <CString, CString> arySctring;
aryString.SetSize(3);

aryString.Add(_T("a1"));
aryString.Add(_T("a222"));
aryString.Add(_T("a3"));

TRACE(_T("%d %s"), aryString.GetCount(), aryString[0]);

the TRACE result is "6 ", it means aryString[0] is no data, I instead of aryString.GetAt(0), the result is same.

Why?

Answer 1

.SetSize(3);

reserve 3 "rooms". Calling

 Add(); 

three times, reserve another 3 "rooms", hence you get 6 at count and your array is as follow:

 \n   
 
 

  
  \n   
  
  
 ""  
\n   
  
  
 ""  
\n   
  
  
 ""  
\n   
  
  
 "a1"  
\n   
  
  
 "a222"  
\n   
  
  
 "a3"  
\n  
 
 

. To get the result I guess you want, once you've set size, you can do:

 aryString.SetSize( 3 ); aryString[0] = "a1"; aryString[1] = "a222"; aryString[2] = "a3"; 

As side note, MFC provides you with CStringArray class, so you haven't to do:

 CArray<CString,CString> 

Answer 2

when you do aryString.SetSize(3); aryString reserves 3 items with empty string. when you Add three new strings at the end , the item count of the array is 6. the first item is empty string, aryString.GetAt[3] will return a1, function add will auto increase the size of the array ,you do not have to SetSize(3) to reserve space

Answer 3

I use as follow code to asign the element

aryString.SetAtGrow(0, _T("a"));
aryString.SetAtGrow(1, _T("a"));