MS Word Automation in C# – Unable to cast object of type ‘System.String[*]’ to type ‘System.String[]’

calendar_today Asked Aug 16, 2011
thumb_up 7 upvotes
history Updated April 14, 2026

Direct Answer

string[] is a vector – a 1-d, 0-based array. string[*], however, is a regular array that just happens to have one dimension. Basically, you are going to have to handle it as…. This is a prose walkthrough, ranked #13th of 32 by community upvote score, from 2011.


The Problem (Q-score 9, ranked #13th of 32 in the Word VBA archive)

The scenario as originally posted in 2011

I use this code to get a String array of headings used in a MS Word 2007 document (.docx):

dynamic arr = Document.GetCrossReferenceItems(WdReferenceType.wdRefTypeHeading);

Using the debugger, I see that arr is dynamically assigned a String array with titles of all my headings in the document (about 40 entries). So far so good.

Then, I want to access the strings, but no matter how I do it, I get the following exception:

InvalidCastException: 
           Unable to cast object of type 'System.String[*]' to type 'System.String[]'.

I have tried different ways of accessing the strings:

By index:

String arr_elem = arr[1];

By casting to an IEnumerable:

IEnumerable list = (IEnumerable)arr;

By using a simple foreach loop:

foreach (String str in arr)
{
   Console.WriteLine(str);
}

However, no matter what I try, I always end up with the same exception as shown above.

Can anyone explain what I am missing here / what I am doing wrong? And especially String[*] – what does it mean?

Why community consensus is tight on this one

Across 32 Word VBA entries in the archive, the accepted answer here holds solid answer (above median) status — meaning voters are unusually aligned on the right fix.


The Verified Solution — solid answer (above median) (+7)

Verbal answer — walkthrough without a code block

Note: the verified answer is a prose walkthrough. If you need a runnable sample, check Word VBA entries ranked in the top 10 of the same archive.

string[] is a vector – a 1-d, 0-based array. string[*], however, is a regular array that just happens to have one dimension. Basically, you are going to have to handle it as Array, and either copy the data out, or use the Array API rather than the string[] API.

This is the same as the difference between typeof(string).MakeArrayType() (the vector) and typeof(string).MakeArrayType(1) (a 1-d non-vector).


When to Use It — vintage (14+ years old, pre-2013)

Ranked #13th in its category — specialized fit

This pattern sits in the 63% tail relative to the top answer. Reach for it when your scenario closely matches the question title; otherwise browse the Word VBA archive for a higher-consensus alternative.

What changed between 2011 and 2026

The answer is 15 years old. The Word VBA object model has been stable across Office 2013, 2016, 2019, 2021, 365, and 2024/2026 LTSC, so the pattern still compiles. Changes that might affect you: 64-bit API declarations (use PtrSafe), blocked macros in downloaded files (Mark-of-the-Web), and the shift toward Office Scripts for web-first workflows.

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Frequently Asked Questions

Is this above-median answer still worth copying?
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Answer score +7 vs the Word VBA archive median ~4; this entry is solid. The score plus 9 supporting upvotes on the question itself (+9) means the asker and 6 subsequent voters all validated the approach.

The answer has no code block — how do I turn it into a snippet?
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Use the walkthrough above as a checklist, then open a top-10 Word VBA archive entry for a concrete starting template you can adapt.

This answer is 15 years old. Is it still relevant in 2026?
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Published 2011, which is 15 year(s) before today’s Office 2026 build. The Word VBA object model has had no breaking changes in that window. Three things to re-test: (1) blocked macros on downloaded files (Mark-of-the-Web), (2) 64-bit API declarations (PtrSafe, LongPtr), (3) any shift toward Office Scripts for web scenarios.

Which Word VBA pattern ranks just above this one at #12?
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The pattern one rank above is “How to put Objective C code into Word (Office) with syntax highlighting”. If your use case overlaps, compare both before committing.

Data source: Community-verified Q&A snapshot. Q-score 9, Answer-score 7, original post 2011, ranked #13th of 32 in the Word VBA archive. Last regenerated April 14, 2026.