生成一段sm4加密算法，c++语言

当然，下面是一个使用C++编写的SM4加密算法示例：

#include <iostream>
#include <cstring>
#include <openssl/evp.h>
#include <openssl/rand.h>

// SM4加密函数
std::string sm4_encrypt(const std::string& plaintext, const std::string& key) {
    EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();
    EVP_EncryptInit_ex(ctx, EVP_sm4_ecb(), nullptr, (const unsigned char*)key.c_str(), nullptr);
    EVP_CIPHER_CTX_set_padding(ctx, EVP_PADDING_PKCS7);

    int ciphertextLen = plaintext.length() + EVP_MAX_BLOCK_LENGTH;
    unsigned char* ciphertext = new unsigned char[ciphertextLen];
    int len;
    EVP_EncryptUpdate(ctx, ciphertext, &len, (const unsigned char*)plaintext.c_str(), plaintext.length());
    int ciphertextLen1 = len;
    EVP_EncryptFinal_ex(ctx, ciphertext + len, &len);
    int ciphertextLen2 = len;

    std::string result;
    result.append((const char*)ciphertext, ciphertextLen1 + ciphertextLen2);

    delete[] ciphertext;
    EVP_CIPHER_CTX_free(ctx);

    return result;
}

int main() {
    std::string plaintext = "Hello, World!";
    std::string key = "1234567890123456";
    
    std::string ciphertext = sm4_encrypt(plaintext, key);
    
    std::cout << "Ciphertext: " << ciphertext << std::endl;

    return 0;
}

请确保你已经安装了OpenSSL库，并将上述代码保存为一个.cpp文件进行编译运行。这个示例使用了OpenSSL提供的SM4算法实现进行加密。