What does C# do when typecasting a letter to an int?

问题

We've to implement an encryption for an external interface. The owner of the interface has given documentation of how to preform the same encryption on our side. However, this documentation is in C# and we work in PHP.

Most of the parts we understand except for where they seem to typecast a hash to an int. Their code reads:

// hashString exists and is a md5 a like string
int[] keyBuffer = new int[hashString.length];
for (int i=0; i<hashString.length; i++) {
    keyBuffer[i] = (int)hashString[i];
}

In PHP, when casting a letter as int, you get 0 (int). As we can't imagine this is what the third party means, we believe C# does something else.

Does C# also cast to int 0, or possibly to a char?

Second, the original hashString is 320 long. This means the code will be creating an int which is 320 long?? In PHP you don't have this idea of reserving memory as C# does here. But when we try to typecast a 320 long string to an int we get an int which is 19 'chars' long.

Does C# also create a shorter int when typecasting a really long 'number' in a string?

回答1:

You're converting a char to int. A char is a UTF-16 code unit - an unsigned 16-bit integer (the range is [0, 65535]). You get that value, basically, widened to a 32-bit signed integer. So 'A' ends up as 65, for example, and the Euro symbol (U+20AC) ends up as 8364 (0x20ac).

As for your second part - you're creating an int, you're creating an int array. An yes, you'll be creating an array with 320 elements.

回答2:

C# strings are UTF16. When you cast a UTF16 character to an int, it merely copies the 16-bit UTF16 character value into the 32-bit int.

回答3:

C# can cast a character to an int and will give you the character code.The code above is taking a string, hashString, and turning it into an array of integers, keybuffer. C# is capable of treating a string like an array of chars using the indexer [] syntax. The code above will produce an array of ints, one per character in the hash string, and each int will be the character code of the corresponding character.

回答4:

To expand on Jon Skeet's post, your "decimal" integer values will map to the corresponding char values like in the chart below (which I have had on my development PCs for years).

So, casting the integer value 0 to a char will return a NULL.

EDIT: Looking at your original question, it is possible you would be better served looking at an MD5 Example instead of casting the string to an array of integers.

回答5:

The code actually cast the char (normally ASCII) into an int, not '0' to 0. So if the original string is "d131dd02c5e6eec4", the resulting array will be int[]{100, 49, 51, 49, 100, 100, 48, 50, 99, 53, 101, 54, 101, 101, 99, 52}.

So I imagine you need the function ord in your PHP script.

EDIT:

A bit remarks, casting a string to int in PHP may actually phrase it into int, and the largest int PHP handles is either 32-bit or 64-bit depending on the OS, that's why you get a 19-char long int, which is the maximum of 64-bit int.

In C#, there is another variable type called char, which represents one unicode character, and can cast directly into integer. You cannot cast a string in C# into an int directly in C#.

EDIT2: I imagine your PHP script to look like this:

<?php
$keyBuffer = new array();
for ($i=0; $i<strlen($hashString); $i++) {
    $keyBuffer[$i] = ord($hashString[i]);
}
?>

来源：https://stackoverflow.com/questions/11102194/what-does-c-sharp-do-when-typecasting-a-letter-to-an-int

标签

php

casting