Usage example:

using System;

namespace MyNamespace
{
    class Sample
    {
        public static void Main()
        {
            int[] src = ...;
            int[] dst = ...;

            // Warn
            Buffer.BlockCopy(src, 0, dst, 0, src.Length);

            // Warn
            Buffer.BlockCopy(src, 0, dst, 0, dst.Length);

            // Warn
            int numBytes2 = src.Length;
            Buffer.BlockCopy(src, 0, dst, 0, numBytes2);

            // Warn
            int numBytes3 = dst.Length;
            Buffer.BlockCopy(src, 0, dst, 0, numBytes3);

            // Do not warn
            Buffer.BlockCopy(src, 0, dst, 0, 5);

            // Do not warn
            int numBytes = ...;
            Buffer.BlockCopy(src, 0, dst, 0, numBytes);

            // Do not warn
            Buffer.BlockCopy(src, 0, dst, 0, GetNumBytes());


           // Allowed array data types
            
            byte[] srcByte = ...;
            byte[] dstByte = ...;

            // Do not warn if underlying array type is byte
            Buffer.BlockCopy(srcByte, 0, dstByte, 0, srcByte.Length);

            // Do not warn if underlying array type is byte
            Buffer.BlockCopy(srcByte, 0, dstByte, 0, dstByte.Length);

            sbyte[] srcSbyte = ...;
            sbyte[] dstSbyte = ...;
            // Do not warn if underlying array type is sbyte
            Buffer.BlockCopy(srcSbyte, 0, dstSbyte, 0, srcSbyte.Length);

            // Do not warn if underlying array type is sbyte
            Buffer.BlockCopy(srcSbyte, 0, dstSbyte, 0, dstSbyte.Length);
        }

        static int GetNumBytes()
        {
            return ...;
        }
    }
}

Suggested severity: warning.
No code fixer expected for this.

Question

@jeffhandley 's last suggestion to detect if a division is used would not warn anyway because the passed argument would not exactly be src.Length or dst.Length, but an expression. Would we be interested in detecting if the expression is src.Length/sizeof(int) or dst.Length/sizeof(int) or a division that would make sense to determine the size in bytes, depending on the data type of the array?

Pass number of bytes to Buffer.BlockCopy #33765

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