CODEWITHSUNDEEP
c#stringutf-8base64ascii
kenny
kenny

Reputation: 1247

C# String confusion compared to Java

I'm confused as a java dev trying his way into C#. I've read about the string type and it being immutable and such , not much different from java except that it doesn't seem to be an object like there but I'm getting weird behavior regardless. I have following toString method on a class

    public override string ToString()
    {
        StringBuilder builder = new StringBuilder();

        builder.Append("BlockType: ");
        builder.Append(BlockType + "\n");
        //builder.Append(System.Text.ASCIIEncoding.ASCII.GetChars(Convert.FromBase64String("dHh0AA==")));
        //builder.Append("\n");
        builder.Append("BlockName: ");
        builder.Append(BlockName + "\n");
        //builder.Append(System.Text.ASCIIEncoding.ASCII.GetChars(Convert.FromBase64String(this.BlockName)));
        //builder.Append("\n");
        builder.Append("BlockLength: " + this.BlockLength + "\n");
        builder.Append("pBlockData: " + this.pBlockData + "\n");
        return builder.ToString();
    }

When I fill it with data. Taking in account that BlockType and BlockName will contain a Base64 String. I get following result

FileVersionNo: 0
nx: 1024
ny: 512
TileSize: 256
HorizScale: 10
Precis: 0,01
ExtHeaderLength: 35
nExtHeaderBlocks: 1
pExtHeaderBlocks: System.Collections.Generic.LinkedList`1[LibFhz.HfzExtHeaderBlock]

BlockType: dHh0AA==
BlockName: YXBwLW5hbWUAAAAAAAAAAA==
BlockLength: 11
pBlockData: System.Byte[]

Which is perfect exactly what I want, however when I try to get the ASCII value of those Base64 (or UTF-8, I tried both) I get the following result

FileVersionNo: 0
nx: 1024
ny: 512
TileSize: 256
HorizScale: 10
Precis: 0,01
ExtHeaderLength: 35
nExtHeaderBlocks: 1
pExtHeaderBlocks: System.Collections.Generic.LinkedList`1[LibFhz.HfzExtHeaderBlock]

BlockType: txt

The code just seems to stop, without error or stacktrace. I have no idea what is going on. I thought first that a \0 is missing so I've added it to the string, then I thought I need a \r\n ... again not the sollution, I started to google with people just wanting to know how to do a Bas64 to UTF-8 conversion ... but that part seems easy ... this code stop isn't.

Any insights or links to decent articles about string handling in .net would be appreciated

Upvotes: 0

Views: 86

Answers (2)

Dweeberly
Dweeberly

Reputation: 4777

First 

builder.Append("pBlockData: " + this.pBlockData + "\n");

Doesn't do what you think it does, specifically if pBlockData is a byte array you will get something like this (output from scriptcs):

> byte[] data = new byte[11];
> StringBuilder sb  = new StringBuilder();
> sb.Append("data = ")
{Capacity:16,MaxCapacity:2147483647,Length:7}
> sb.Append(data);
{Capacity:32,MaxCapacity:2147483647,Length:20}
> sb.ToString()
data = System.Byte[]

Second C# strings (.NET strings in general) are UTF-16, so it doesn't really know how to handle displaying bytes. It doesn't matter if it is bas64 encoded or ASCII or French pickles ;-) the runtime just treats it as binary. Also null termination is not required, the length of the string is kept as a property of the string object.

So you need to turn the byte array you have into a UTF-16 character array, or string before you output it. If the byte array contains valid ASCII you can look into the 'System.Text.ASCIIEncoding.ASCII.GetDecoder().Convert' method as one way to accomplish this.

Upvotes: 1

Matthew Watson
Matthew Watson

Reputation: 109597

I've had a look at what you get from this:

var test = Convert.FromBase64String("YXBwLW5hbWUAAAAAAAAAAA==");
var builder = new StringBuilder();
builder.Append(System.Text.Encoding.ASCII.GetChars(test));

The answer is the string "app-name" with a load of null (0) characters at the end.

You could try removing all the null characters by adding this line just before you return builder.ToString():

builder.Replace("\0", null);

That may or may not help, depending on what you're doing with the returned string.

Upvotes: 1

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