#include <openssl/md5.h>
#include <openssl/err.h>
//1.计算字符串
    unsigned char MD5result[128]={0};
    unsigned char  inStr[4]={‘1‘,‘2‘,‘3‘,‘4‘} ;
    size_t inStrSize=sizeof(inStr);
    MD5(inStr,inStrSize,MD5result); //获取字符串的MD5值
//2.计算文件
    unsigned char MD5result[128]={0};
    MD5_CTX md5_ctx;
    MD5_Init(&md5_ctx);
    char readData[2048]={0};
    while(!rfile.eof())
    {
        rfile.read(ReadBuff,sizeof(readBuff));   //以二进制方式读需要计算MD5的文件
        int rlength = rfile.gcount();
        if(rlength>0)
        {
            MD5_Update(&md5_ctx,readBuff,rlength); //将当前文件块加入，并更新MD5
        }
    }
    MD5_Final(MD5result,&md5_ctx);  //获取MD5值