Question

What is the difference between the following coding ways:

if (String::IsNullOrEmpty(TextBox1->Text)) 

and

if (TextBox1->Text == "") 

?

Answer 1

The first one checks for null as well.

A TextBox->Text property will never be null but consider (C#):

string s1 = null;
string s2 = "";

string.IsNullOrEmpty(s1)    // true
string.IsNullOrEmpty(s2)    // true

s1 == ""    // false
s2 == ""    // true

The IsNullOrEmpty() function is just a handy helper to check 2 (error) conditions at once.

So your title is slightly off, this is about empty and null. Because:

string.Empty == ""     // true

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A string is an object. s1 and s2 are not strings but references (pointers) to strings. null is a special reference value meaning ‘not pointing to an object’. An empty string is a valid string object with length=0