How to get the MD5 hash of a file in C

Question

I ve the file path  How can I get the MD5 hash of it

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I use this file http   people csail mit edu rivest Md5 c

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QFile file  bigimage jpg     if  file open QIODevice  ReadOnly         QByteArray fileData   file readAll         QByteArray hashData   QCryptographicHash  hash fileData QCryptographicHash  Md5      or QCryptographicHash  Sha1     qDebug    lt  lt  hashData toHex        0e0c2180dfd784dd84423b00af86e2fc

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Using Crypto    you could do the following     include  lt sha h gt   include  lt iostream gt    SHA256 sha   while    f eof           char buff 4096      int numchars   f read           sha Update buff  numchars      char hash size    sha Final hash    cout  lt  lt  hash  lt  lt endl     I have a need for something very similar  because I can t read in multi-gigabyte files just to compute a hash   In theory I could memory map them  but I have to support 32bit platforms - that s still problematic for large files

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I needed to do this just now and required a cross-platform solution that was suitable for c  11  boost and openssl  I took D Nabre s solution as a starting point and boiled it down to the following    include  lt openssl md5 h gt   include  lt iomanip gt   include  lt sstream gt   include  lt boost iostreams device mapped file hpp gt   const std  string md5 from file const std  string amp  path        unsigned char result MD5 DIGEST LENGTH       boost  iostreams  mapped file source src path       MD5  unsigned char  src data    src size    result        std  ostringstream sout      sout lt  lt std  hex lt  lt std  setfill  0        for auto c  result  sout lt  lt std  setw 2  lt  lt  int c       return sout str        A quick test executable demonstrates    include  lt iostream gt   int main int argc  char  argv          if argc    2            std  cerr lt  lt  Must specify the file n           exit -1             std  cout lt  lt md5 from file argv 1   lt  lt      lt  lt argv 1  lt  lt std  endl      return 0      Some linking notes  Linux  -lcrypto -lboost iostreams Windows  -DBOOST ALL DYN LINK libeay32 lib ssleay32 lib

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For anyone redirected from  https   stackoverflow com questions 4393017 md5-implementation-in-c  because it s been incorrectly labelled a duplicate   The example located here works   http   www zedwood com article cpp-md5-function  If you are compiling in VC  2010 then you will need to change his main cpp to this    include  lt iostream gt    for std  cout  include  lt string h gt    for std  string  include  MD5 h   using std  cout  using std  endl   int main int argc  char  argv          std  string Temp    md5  The quick brown fox jumps over the lazy dog        cout  lt  lt  Temp c str    lt  lt  endl       return 0      You will have to change the MD5 class slightly if you are to read in a char   array instead of a string to answer the question on this page here   EDIT   Apparently modifying the MD5 library isn t clear  well a Full VC  2010 solution is here for your convenience to include char   s   https   github com alm4096 MD5-Hash-Example-VS  A bit of an explanation is here    include  lt iostream gt    for std  cout  include  lt string h gt    for std  string  include  lt fstream gt   include  MD5 h   using std  cout  using std  endl   int main int argc  char  argv            Start opening your file     ifstream inBigArrayfile      inBigArrayfile open   Data dat   std  ios  binary   std  ios  in          Find length of file     inBigArrayfile seekg  0  std  ios  end       long Length   inBigArrayfile tellg        inBigArrayfile seekg  0  std  ios  beg              read in the data from your file     char   InFileData   new char Length       inBigArrayfile read InFileData Length          Calculate MD5 hash     std  string Temp    md5 InFileData Length       cout  lt  lt  Temp c str    lt  lt  endl         Clean up     delete    InFileData       return 0      I have simply added the following into the MD5 library   MD5 cpp   MD5  MD5 char   Input  long length      init      update Input  length     finalize        MD5 h   std  string md5 char   Input  long length

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You can implement the MD5 algorithm yourself  examples are all over the web   or you can link against the OpenSSL libs and use OpenSSL s digest functions  here s an example to get the MD5 of a byte array    include  lt openssl md5 h gt  QByteArray AESWrapper  md5   const QByteArray amp  data        unsigned char   tmp hash      tmp hash   MD5  const unsigned char  data constData    data length    NULL       return QByteArray  const char  tmp hash  MD5 DIGEST LENGTH

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md5 h also have MD5   functions very useful for big file   include  lt openssl md5 h gt   include  lt fstream gt           std  ifstream file filename  std  ifstream  binary   MD5 CTX md5Context  MD5 Init  amp md5Context   char buf 1024   16   while  file good          file read buf  sizeof buf        MD5 Update  amp md5Context  buf  file gcount       unsigned char result MD5 DIGEST LENGTH   MD5 Final result   amp md5Context     Very simple  isn t it  Convertion to string also very simple    include  lt sstream gt   include  lt iomanip gt           std  stringstream md5string  md5string  lt  lt  std  hex  lt  lt  std  uppercase  lt  lt  std  setfill  0    for  const auto  amp byte  result      md5string  lt  lt  std  setw 2   lt  lt   int byte   return md5string str

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John Walker s implementation comes with sources

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Here s a straight forward implementation of the md5sum command that computes and displays the MD5 of the file specified on the command-line  It needs to be linked against the OpenSSL library  gcc md5 c -o md5 -lssl  to work  It s pure C  but you should be able to adapt it to your C   application easily enough    include  lt sys types h gt   include  lt sys stat h gt   include  lt sys mman h gt   include  lt fcntl h gt   include  lt stdio h gt   include  lt stdlib h gt   include  lt string h gt    include  lt openssl md5 h gt   unsigned char result MD5 DIGEST LENGTH       Print the MD5 sum as hex-digits  void print md5 sum unsigned char  md        int i      for i 0  i  lt MD5 DIGEST LENGTH  i                  printf   02x  md i                Get the size of the file by its file descriptor unsigned long get size by fd int fd        struct stat statbuf      if fstat fd   amp statbuf   lt  0  exit -1       return statbuf st size     int main int argc  char  argv          int file descript      unsigned long file size      char  file buffer       if argc    2                 printf  Must specify the file n                exit -1             printf  using file  t s n   argv 1         file descript   open argv 1   O RDONLY       if file descript  lt  0  exit -1        file size   get size by fd file descript       printf  file size  t lu n   file size        file buffer   mmap 0  file size  PROT READ  MAP SHARED  file descript  0       MD5  unsigned char   file buffer  file size  result       munmap file buffer  file size         print md5 sum result       printf     s n   argv 1         return 0

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I have used Botan to perform this operation and others before  AraK has pointed out Crypto    I guess both libraries are perfectly valid  Now it is up to you  -

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A rework of impementation by  D Nabre for C    Don t forget to compile with -lcrypto at the end  gcc md5 c -o md5 -lcrypto    include  lt iostream gt   include  lt iomanip gt   include  lt fstream gt   include  lt string gt    include  lt openssl md5 h gt  using namespace std   unsigned char result MD5 DIGEST LENGTH       function to print MD5 correctly void printMD5 unsigned char  md  long size   MD5 DIGEST LENGTH        for  int i 0  i lt size  i              cout lt  lt  hex  lt  lt  setw 2   lt  lt  setfill  0    lt  lt   int  md i            int main int argc  char  argv       if argc    2        cout  lt  lt   Specify the file      lt  lt  endl      return 0     ifstream  pos type fileSize  char   memBlock   ifstream file  argv 1   ios  ate      check if opened if  file is open       cout lt  lt   Using file t  lt  lt  argv 1  lt  lt endl    else       cout lt  lt   Unnable to open t  lt  lt  argv 1  lt  lt endl      return 0       get file size  amp  copy file to memory     file seekg -1 ios  end      exludes EOF fileSize   file tellg    cout  lt  lt   File size  t  lt  lt  fileSize  lt  lt  endl  memBlock   new char fileSize   file seekg 0 ios  beg   file read memBlock  fileSize   file close       get md5 sum MD5  unsigned char   memBlock  fileSize  result        cout  lt  lt   MD5 DIGEST LENGTH     lt  lt  MD5 DIGEST LENGTH  lt  lt  endl  printMD5 result   cout lt  lt endl   return 0

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There is a pretty library at http   256stuff com sources md5   with example of use  This is the simplest library for MD5

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