c++ 哈希加密

#include <stdio.h>　　//sprintf() 需要用到该库
#include <string.h>
#include <iostream>
#include <string>

using namespace std;

#include <openssl/sha.h>
string sha256(const string str)
{
    char buf[2];
    unsigned char hash[SHA256_DIGEST_LENGTH];
    SHA256_CTX sha256;
    SHA256_Init(&sha256);
    SHA256_Update(&sha256, str.c_str(), str.size());
    SHA256_Final(hash, &sha256);
    std::string NewString = "";
    for(int i = 0; i < SHA256_DIGEST_LENGTH; i++)
    {
        sprintf(buf,"%02x",hash[i]);
        NewString = NewString + buf;
    }
        return NewString;
}

int main() {
    string x;
    cout<<"Please enter:";
    getline(cin,x);
    cout << sha256(x) << endl;
    return 0;
}

g++ -lssl -lcrypto -o sha256 sha256.cpp