how to get md5sum command and get the string output in code

Question

I'm writing a code in C++ and I wish to get the md5 checksum of a certain string. I know I can run system("echo "myStirng" | md5sum > some_file.txt") and then read the file. I'm writing code for an embedded system and due to performance issues I don't wan't to use file operations. also, I can't use any openSSL functions in my code. I did my searching and all the answers I came across either included some file operations or used openSSL functions. Is there a way to get the md5 checksum without using file operations and without using openSSL? maybe running the linux command md5sum as a different process from the code like the C function system does, but returning the checksum hex string and not the return code.

Thanks you.

Have a look at http://stackoverflow.com/questions/3395690/md5sum-of-file-in-linux-c — slugonamission, Dec 05 '13 at 11:33
@slugonamission this solution will require me to download and install openSSL, is there a way to avoid it? — eladm26, Dec 05 '13 at 11:50
@eladm26 Why would it require you to download/install openSSL? You should just be able to link it like so: `-lssl -lcrypto`. — , Dec 05 '13 at 11:56

score 0 · Accepted Answer · edited Feb 28 '17 at 20:49

This is a proof of concept I wrote some time ago. Pretty much like the second answer in the link in @slugonmission 's comment but a bit better I think (using fread). Actually at the end I preferred the approach using the library as a little bit faster. So I suggest if dependency on openssl is ok with you and performance is important to prefer the library.

FILE* pipe = popen("md5sum /home/bla.txt", "r");                                                                                       
if (pipe != NULL)                                                                                                                                                    
{                                                                                                                                                     
  static const unsigned md5size = 32;                                                                                                                 
  unsigned char md5res[md5size + 1];                                                                                                                  
  int readSize = fread((void*) md5res, sizeof(char), md5size, pipe);                                                                                  
  if (readSize != md5size)                                                                                                                            
  {                                                                                                                                                    
      std::cout << "Error reading md5" << std::endl;                                                                                                     
      return 1;                                                                                                                                          
  }                                                                                                                                                    
  pclose(pipe);                                                                                                                        
  md5res[md5size] = 0;    
 }

thank you for your answer. but this answer includes files, do you think there is option to solve it without using files, maybe using md5sum linux command somehow? — eladm26, Dec 08 '13 at 12:58

score 0 · Answer 2 · answered Dec 05 '13 at 11:52

0

Use http://hashlib2plus.sourceforge.net/ then run something like:

#include <hashlibpp.h>
#include <string>

int main() {
    hashwrapper *rap = new md5wrapper();
    std::string hash = rap->getHashFromFile("README.TXT");
}

answered Dec 05 '13 at 11:52

Paul Evans

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Thank you for the help but I can't use this library. – eladm26 Dec 08 '13 at 13:00

how to get md5sum command and get the string output in code

2 Answers2