Best way to read a large file into a byte array in C

Question

I have a web server which will read large binary files  several megabytes  into byte arrays  The server could be reading several files at the same time  different page requests   so I am looking for the most optimized way for doing this without taxing the CPU too much  Is the code below good enough   public byte   FileToByteArray string fileName        byte   buff   null      FileStream fs   new FileStream fileName                                      FileMode Open                                      FileAccess Read       BinaryReader br   new BinaryReader fs       long numBytes   new FileInfo fileName  Length      buff   br ReadBytes  int  numBytes       return buff

User · Answer

use this    bytesRead   responseStream ReadAsync buffer  0  Length  Result

User · Answer

I would recommend trying the Response TransferFile   method then a Response Flush   and Response End   for serving your large files

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I might argue that the answer here generally is  don t   Unless you absolutely need all the data at once  consider using a Stream-based API  or some variant of reader   iterator   That is especially important when you have multiple parallel operations  as suggested by the question  to minimise system load and maximise throughput   For example  if you are streaming data to a caller   Stream dest       using Stream source   File OpenRead path         byte   buffer   new byte 2048       int bytesRead      while  bytesRead   source Read buffer  0  buffer Length    gt  0            dest Write buffer  0  bytesRead

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In case with  a large file  is meant beyond the 4GB limit  then my following written code logic is appropriate   The key issue to notice is the LONG data type used with the SEEK method  As a LONG is able to point beyond 2 32 data boundaries  In this example  the code is processing first processing the large file in chunks of 1GB  after the large whole 1GB chunks are processed  the left over   lt 1GB  bytes are processed  I use this code with calculating the CRC of files beyond the 4GB size   using https   crc32c machinezoo com  for the crc32c calculation in this example   private uint Crc32CAlgorithmBigCrc string fileName        uint hash   0      byte   buffer   null      FileInfo fileInfo   new FileInfo fileName       long fileLength   fileInfo Length      int blockSize   1024000000      decimal div   fileLength   blockSize      int blocks    int Math Floor div       int restBytes    int  fileLength -  blocks   blockSize        long offsetFile   0      uint interHash   0      Crc32CAlgorithm Crc32CAlgorithm   new Crc32CAlgorithm        bool firstBlock   true      using  FileStream fs   new FileStream fileName  FileMode Open  FileAccess Read                 buffer   new byte blockSize           using  BinaryReader br   new BinaryReader fs                         while  blocks  gt  0                                blocks -  1                  fs Seek offsetFile  SeekOrigin Begin                   buffer   br ReadBytes blockSize                   if  firstBlock                                        firstBlock   false                      interHash   Crc32CAlgorithm Compute buffer                       hash   interHash                                    else                                       hash   Crc32CAlgorithm Append interHash  buffer                                     offsetFile    blockSize                            if  restBytes  gt  0                                Array Resize ref buffer  restBytes                   fs Seek offsetFile  SeekOrigin Begin                   buffer   br ReadBytes restBytes                   hash   Crc32CAlgorithm Append interHash  buffer                             buffer   null                        MessageBox Show hash ToString           MessageBox Show hash ToString  X         return hash

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Use the BufferedStream class in C  to improve performance  A buffer is a block of bytes in memory used to cache data  thereby reducing the number of calls to the operating system  Buffers improve read and write performance   See the following for a code example and additional explanation  http   msdn microsoft com en-us library system io bufferedstream aspx

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Simply replace the whole thing with   return File ReadAllBytes fileName     However  if you are concerned about the memory consumption  you should not read the whole file into memory all at once at all  You should do that in chunks

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I would think this   byte   file   System IO File ReadAllBytes fileName

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Your code can be factored to this  in lieu of File ReadAllBytes    public byte   ReadAllBytes string fileName        byte   buffer   null      using  FileStream fs   new FileStream fileName  FileMode Open  FileAccess Read                 buffer   new byte fs Length           fs Read buffer  0   int fs Length             return buffer       Note the Integer MaxValue - file size limitation placed by the Read method   In other words you can only read a 2GB chunk at once   Also note that the last argument to the FileStream is a buffer size   I would also suggest reading about FileStream and BufferedStream   As always a simple sample program to profile which is fastest will be most beneficial   Also your underlying hardware will have a large effect on performance   Are you using server based hard disk drives with large caches and a RAID card with onboard memory cache   Or are you using a standard drive connected to the IDE port

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If you re dealing with files above 2 nbsp GB  you ll find that the above methods fail   It s much easier just to hand the stream off to MD5 and allow that to chunk your file for you   private byte   computeFileHash string filename        MD5 md5   MD5 Create        using  FileStream fs   new FileStream filename  FileMode Open                 byte   hash   md5 ComputeHash fs           return hash

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Depending on the frequency of operations  the size of the files  and the number of files you re looking at  there are other performance issues to take into consideration   One thing to remember  is that each of your byte arrays will be released at the mercy of the garbage collector   If you re not caching any of that data  you could end up creating a lot of garbage and be losing most of your performance to   Time in GC  If the chunks are larger than 85K  you ll be allocating to the Large Object Heap LOH  which will require a collection of all generations to free up  this is very expensive  and on a server will stop all execution while it s going on    Additionally  if you have a ton of objects on the LOH  you can end up with LOH fragmentation  the LOH is never compacted  which leads to poor performance and out of memory exceptions   You can recycle the process once you hit a certain point  but I don t know if that s a best practice   The point is  you should consider the full life cycle of your app before necessarily just reading all the bytes into memory the fastest way possible or you might be trading short term performance for overall performance

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Overview  if your image is added as a action  embedded resource then use the GetExecutingAssembly to retrieve the jpg resource into a stream then read the binary data in the stream into an byte array     public byte   GetAImage                 byte   bytes null          var assembly   Assembly GetExecutingAssembly            var resourceName    MYWebApi Images X my image jpg            using  Stream stream   assembly GetManifestResourceStream resourceName                         bytes   new byte stream Length               stream Read bytes  0   int stream Length                     return bytes

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I d say BinaryReader is fine  but can be refactored to this  instead of all those lines of code for getting the length of the buffer   public byte   FileToByteArray string fileName        byte   fileData   null       using  FileStream fs   File OpenRead fileName                   using  BinaryReader binaryReader   new BinaryReader fs                         fileData   binaryReader ReadBytes  int fs Length                        return fileData      Should be better than using  ReadAllBytes    since I saw in the comments on the top response that includes  ReadAllBytes   that one of the commenters had problems with files   600 MB  since a BinaryReader is meant for this sort of thing   Also  putting it in a using statement ensures the FileStream and BinaryReader are closed and disposed

[c#] Best way to read a large file into a byte array in C#?

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