.net – which is the best way to initialize a string with null in vb.net

initializationnetstringvb.net

We can declare and initialize a string variable in vb.net in following ways:

 Dim str1 As String = ""
 Dim str2 As String = Nothing
 Dim str3 As String = vbNullString

Question :

Which one is the best programming practice?
What is the difference between these three methods?

Best Answer

A string will be set to Nothing until you specify otherwise, so there is no need to initialise it like this:

Dim s As String = Nothing

because this is just the same as

Dim s As String

You may want to set it Nothing later on in your code but not at initialisation,

vbNullString is a carry over from VB6 days and is functionally equivalent to Nothing

A blank string ("") and String.Empty are equivalent.

Some say String.Empty has a slight performance advantage but I don't see any evidence.

Note: The IL produced by these two is different:

"" produces:

IL_0001:  ldstr      ""

String.Empty produces:

IL_0001:  ldsfld     string [mscorlib]System.String::Empty

So to answer your question:

Dim str1 As String = "" 'Initialises as blank string same as String.Empty
Dim str2 As String = Nothing 'Same as Dim str2 As String
Dim str3 As String = vbNullString 'Same as previous line but deprecated so avoid

So you should be using the following if you want an empty string

Dim s As String = ""

And the following if you want a Null (Nothing) string:

Dim s As String

Which one you want depends on what you are doing

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C++ – How to iterate over the words of a string

I use this to split string by a delimiter. The first puts the results in a pre-constructed vector, the second returns a new vector.

#include <string>
#include <sstream>
#include <vector>
#include <iterator>

template <typename Out>
void split(const std::string &s, char delim, Out result) {
    std::istringstream iss(s);
    std::string item;
    while (std::getline(iss, item, delim)) {
        *result++ = item;
    }
}

std::vector<std::string> split(const std::string &s, char delim) {
    std::vector<std::string> elems;
    split(s, delim, std::back_inserter(elems));
    return elems;
}

Note that this solution does not skip empty tokens, so the following will find 4 items, one of which is empty:

std::vector<std::string> x = split("one:two::three", ':');

Best Answer

Related Solutions

C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

C++ – How to iterate over the words of a string

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