C Returned char from GetSaveFileName() contains null characters

I'm using the following code to get the filepath to save to for use with tinyxml2:

OPENFILENAME ofn;

char szFileName[MAX_PATH] = "";

ZeroMemory(&ofn, sizeof(ofn));
ofn.lStructSize = sizeof(ofn); 
ofn.hwndOwner = NULL;
ofn.lpstrFilter = (LPCWSTR)L"XML Files (*.xml)\0*.xml\0All Files (*.*)\0*.*\0";
ofn.lpstrFile = (LPWSTR)szFileName;
ofn.lpstrFile[0] = '\0';
ofn.nMaxFile = MAX_PATH;
ofn.Flags = OFN_EXPLORER | OFN_FILEMUSTEXIST | OFN_HIDEREADONLY;
ofn.lpstrDefExt = (LPCWSTR)L"xml";
GetSaveFileName(&ofn);

This works fine and displays the Dialog box however when I look up the returned value in szFileName it seems to contain many null characters:

szFileName  0x0026f5b0 "C"  char[0x00000104]
[0x00000000]    0x43 'C'    char
[0x00000001]    0x00 '\0'   char
[0x00000002]    0x3a ':'    char
[0x00000003]    0x00 '\0'   char
[0x00000004]    0x5c '\\'   char
[0x00000005]    0x00 '\0'   char
[0x00000006]    0x61 'a'    char
[0x00000007]    0x00 '\0'   char
[0x00000008]    0x73 's'    char
[0x00000009]    0x00 '\0'   char
[0x0000000a]    0x64 'd'    char
[0x0000000b]    0x00 '\0'   char
[0x0000000c]    0x61 'a'    char
[0x0000000d]    0x00 '\0'   char
[0x0000000e]    0x73 's'    char
[0x0000000f]    0x00 '\0'   char
[0x00000010]    0x64 'd'    char
[0x00000011]    0x00 '\0'   char
[0x00000012]    0x61 'a'    char
[0x00000013]    0x00 '\0'   char
[0x00000014]    0x73 's'    char
[0x00000015]    0x00 '\0'   char
[0x00000016]    0x2e '.'    char
[0x00000017]    0x00 '\0'   char
[0x00000018]    0x78 'x'    char
[0x00000019]    0x00 '\0'   char
[0x0000001a]    0x6d 'm'    char
[0x0000001b]    0x00 '\0'   char
[0x0000001c]    0x6c 'l'    char

This when passed into tinyxml2 ends up saving a file with which the name is 1 character long, and the first char in szFileName.

Why would it be adding in these null characters after each character?

You are calling GetSaveFileNameW instead of GetSaveFileNameA. Declare szFileName as array of TCHAR (or WCHAR).

The name GetSaveFileName will resolve to the name GetSaveFileNameW or GetSaveFileNameA depending on the #define in your code (or project settings). By default it defines _UNICODE ("wide charaters") in modern Visual Studio versions.

If you pass it on to another library that expects a certain character set, you may have to convert using WideCharToMultiByte or related functions.

Also: don't forcibly coerce one type into an incompatible different type like you do with szFileName (being char[MAX_PATH]) and (LPWSTR).