C++中这行代码的含义

Question

我刚开始拿起C,我正在使用代码中的RSA密码.但是,这行代码让我很困惑.积分在此处从此站点发送给作者.

char* intmsg = new char[strlen(msg)*3 + 1];

这是可以找到该行的方法.

inline void encrypt(char* msg,FILE* fout)
{
    /* This function actually does the encrypting of each message */

    unsigned int i;
    int tmp;
    char tmps[4];
    char* intmsg = new char[strlen(msg)*3 + 1];


    /* Here, (mpz_t) M is the messsage in gmp integer 
    *  and (mpz_t) c is the cipher in gmp integer */

    char ciphertext[1000];

    strcpy(intmsg,"");

    for(i=0;i<strlen(msg);i++)
    {
        tmp = (int)msg[i];

        /* print it in a 3 character wide format */
        sprintf(tmps,"%03d",tmp);

        strcat(intmsg,tmps);
    }

    mpz_set_str(M,intmsg,10);

    /* free memory claimed by intmsg */
    delete [] intmsg;

    /* c = M^e(mod n) */
    mpz_powm(c,M,e,n);

    /* get the string representation of the cipher */
    mpz_get_str(ciphertext,10,c);

    /* write the ciphertext to the output file */
    fprintf(fout,"%s\n",ciphertext);
}

Answer 1

该代码行实际上不是C,它是C++.

    char* intmsg = new char[strlen(msg)*3 + 1];

意味着为给定数量的字符动态分配具有空间的内存块,比msg字符串的原始长度大3倍+ 1 .

C等效将是

    char* intmsg = malloc(strlen(msg)*3 + 1);

要解除分配该内存块,delete []intmsg可以在C++中使用,而如果malloc在C中使用,则可以使用free(intmsg);