怎样用 C# 快速比较 2 个文件是否是相同的文件？

方案1：

直接贴代码了：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace FileCompareDemo
{
    public class FileHelper
    {
        const int BYTES_TO_READ = sizeof(Int64);

        public static bool FilesAreEqual(FileInfo first, FileInfo second)
        {
            if (first.Length != second.Length)
                return false;

            if (string.Equals(first.FullName, second.FullName, StringComparison.OrdinalIgnoreCase))
                return true;

            int iterations = (int)Math.Ceiling((double)first.Length / BYTES_TO_READ);

            using (FileStream fs1 = first.OpenRead())
            using (FileStream fs2 = second.OpenRead())
            {
                byte[] one = new byte[BYTES_TO_READ];
                byte[] two = new byte[BYTES_TO_READ];

                for (int i = ; i < iterations; i++)
                {
                    fs1.Read(one, , BYTES_TO_READ);
                    fs2.Read(two, , BYTES_TO_READ);

                    if (BitConverter.ToInt64(one, ) != BitConverter.ToInt64(two, ))
                        return false;
                }
            }

            return true;
        }

        public static bool FilesAreEqual_OneByte(FileInfo first, FileInfo second)
        {
            if (first.Length != second.Length)
                return false;

            if (string.Equals(first.FullName, second.FullName, StringComparison.OrdinalIgnoreCase))
                return true;

            using (FileStream fs1 = first.OpenRead())
            using (FileStream fs2 = second.OpenRead())
            {
                for (int i = ; i < first.Length; i++)
                {
                    if (fs1.ReadByte() != fs2.ReadByte())
                        return false;
                }
            }

            return true;
        }

        public static bool FilesAreEqual_Hash(FileInfo first, FileInfo second)
        {
            byte[] firstHash = MD5.Create().ComputeHash(first.OpenRead());
            byte[] secondHash = MD5.Create().ComputeHash(second.OpenRead());

            for (int i = ; i < firstHash.Length; i++)
            {
                if (firstHash[i] != secondHash[i])
                    return false;
            }
            return true;
        }
    }
}

方案2：

直接贴代码了：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FileCompareDemo
{
    public static class FileHelper2
    {
        public static bool FilesContentsAreEqual(FileInfo fileInfo1, FileInfo fileInfo2)
        {
            if (fileInfo1 == null)
            {
                throw new ArgumentNullException(nameof(fileInfo1));
            }

            if (fileInfo2 == null)
            {
                throw new ArgumentNullException(nameof(fileInfo2));
            }

            if (string.Equals(fileInfo1.FullName, fileInfo2.FullName, StringComparison.OrdinalIgnoreCase))
            {
                return true;
            }

            if (fileInfo1.Length != fileInfo2.Length)
            {
                return false;
            }
            else
            {
                using (var file1 = fileInfo1.OpenRead())
                {
                    using (var file2 = fileInfo2.OpenRead())
                    {
                        return StreamsContentsAreEqual(file1, file2);
                    }
                }
            }
        }

        private static int ReadFullBuffer(Stream stream, byte[] buffer)
        {
            int bytesRead = ;
            while (bytesRead < buffer.Length)
            {
                int read = stream.Read(buffer, bytesRead, buffer.Length - bytesRead);
                if (read == )
                {
                    // Reached end of stream.
                    return bytesRead;
                }

                bytesRead += read;
            }

            return bytesRead;
        }

        private static bool StreamsContentsAreEqual(Stream stream1, Stream stream2)
        {
            const int bufferSize =  * sizeof(Int64);
            var buffer1 = new byte[bufferSize];
            var buffer2 = new byte[bufferSize];

            while (true)
            {
                int count1 = ReadFullBuffer(stream1, buffer1);
                int count2 = ReadFullBuffer(stream2, buffer2);

                if (count1 != count2)
                {
                    return false;
                }

                if (count1 == )
                {
                    return true;
                }

                int iterations = (int)Math.Ceiling((double)count1 / sizeof(Int64));
                for (int i = ; i < iterations; i++)
                {
                    if (BitConverter.ToInt64(buffer1, i * sizeof(Int64)) != BitConverter.ToInt64(buffer2, i * sizeof(Int64)))
                    {
                        return false;
                    }
                }
            }
        }
    }
}

方案3（异步版本）：

直接贴代码了：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FileCompareDemo
{
    public static class FileCompareAsyncHelper
    {
        static void test(string filePath1, string filePath2)
        {
            var fi1 = new FileInfo(filePath1);
            var fi2 = new FileInfo(filePath2);
            Console.WriteLine(FilesContentsAreEqualAsync(fi1, fi2).GetAwaiter().GetResult());
        }

        public static async Task<bool> FilesContentsAreEqualAsync(FileInfo fileInfo1, FileInfo fileInfo2)
        {
            if (fileInfo1 == null)
            {
                throw new ArgumentNullException(nameof(fileInfo1));
            }

            if (fileInfo2 == null)
            {
                throw new ArgumentNullException(nameof(fileInfo2));
            }

            if (string.Equals(fileInfo1.FullName, fileInfo2.FullName, StringComparison.OrdinalIgnoreCase))
            {
                return true;
            }

            if (fileInfo1.Length != fileInfo2.Length)
            {
                return false;
            }
            else
            {
                using (var file1 = fileInfo1.OpenRead())
                {
                    using (var file2 = fileInfo2.OpenRead())
                    {
                        return await StreamsContentsAreEqualAsync(file1, file2).ConfigureAwait(false);
                    }
                }
            }
        }

        private static async Task<int> ReadFullBufferAsync(Stream stream, byte[] buffer)
        {
            int bytesRead = ;
            while (bytesRead < buffer.Length)
            {
                int read = await stream.ReadAsync(buffer, bytesRead, buffer.Length - bytesRead).ConfigureAwait(false);
                if (read == )
                {
                    // Reached end of stream.
                    return bytesRead;
                }

                bytesRead += read;
            }

            return bytesRead;
        }

        private static async Task<bool> StreamsContentsAreEqualAsync(Stream stream1, Stream stream2)
        {
            const int bufferSize =  * sizeof(Int64);
            var buffer1 = new byte[bufferSize];
            var buffer2 = new byte[bufferSize];

            while (true)
            {
                int count1 = await ReadFullBufferAsync(stream1, buffer1).ConfigureAwait(false);
                int count2 = await ReadFullBufferAsync(stream2, buffer2).ConfigureAwait(false);

                if (count1 != count2)
                {
                    return false;
                }

                if (count1 == )
                {
                    return true;
                }

                int iterations = (int)Math.Ceiling((double)count1 / sizeof(Int64));
                for (int i = ; i < iterations; i++)
                {
                    if (BitConverter.ToInt64(buffer1, i * sizeof(Int64)) != BitConverter.ToInt64(buffer2, i * sizeof(Int64)))
                    {
                        return false;
                    }
                }
            }
        }
    }
}

谢谢浏览！