How to get the MD5 hash of a file in C++? [closed]

Question

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

Answer 1

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 <sys/types.h> #include <sys/stat.h> #include <sys/mman.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <string.h>  #include <openssl/md5.h>  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 <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, &statbuf) < 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 < 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; }