在c [duplicate]中的memcpy之后的字符串末尾的垃圾字符appendind

Question

这个问题在这里已有答案：

• Is null character included while allocating using malloc 4个答案

我正在学习C.在下面的代码中，当我尝试做memcpy时，它最后添加了垃圾字符。没有得到我想念的东西。请帮忙。

int threshold = passlen - type;
 printf("THRESHOLD: %d\n",threshold);
 printf("TYPE: %d\n",type);
 printf("decodedpass: %s len(decodepass): %d\n",decodedpass,strlen(decodedpass));
  strncpy(salt, &decodedpass[threshold] , type);
 printf("-------SALT: %s\n",salt);
  salt[type] = '\0';
 printf("-------LASTSALT: %s\n",salt);
  saltlen = strlen(salt);
 printf("-------SALTLEN: %d\n",saltlen);
  int len = saltlen + userpasslen;
 printf("-------USERPASS: %s\n",userpass);
 printf("-------LENSALTandUSERPASSLEN: %d\n",len);
  createpass = xcalloc(len, sizeof(char));
  memcpy(createpass, userpass, userpasslen);
 printf("-------len(createpass):%d userpasslen:%d len(salt):%d saltlen:%d salt:%s\n",strlen(createpass),userpasslen,strlen(salt),saltlen,salt);
 printf("-------CREATEPASSmemcpy1: %s\n",createpass);
  memcpy(createpass + userpasslen, salt, saltlen);
 printf("-------CREATEPASSmemcpy2: %s len(createpass):%d\n",createpass,strlen(createpass));

OUTPUT：

THRESHOLD: 20
TYPE: 8
decodedpass: G�f�ɴ�=-$�o�   :K���R12345678 len(decodepass): 28
-------SALT: 12345678
-------LASTSALT: 12345678
-------SALTLEN: 8
-------USERPASS: 1234567890123456
-------LENSALTandUSERPSSLEN: 24
-------len(createpass):16 userpasslen:16 len(salt):8 saltlen:8 salt:12345678
-------CREATEPASSmemcpy1: 1234567890123456
-------CREATEPASSmemcpy2: 123456789012345612345678� len(createpass):26

Answer 1

因为在内存中的字符串末尾没有空包。分配内存时，必须考虑这种情况。然后，有两种方法可以解决您的问题：

1)

createpass = xcalloc(len+1, sizeof(char));
memset(createpass, 0, len+1);

要么

2)

createpass = xcalloc(len+1, sizeof(char));
memset(createpass, 0, len+1);  // option, because the 'sprintf' will fill a '\0' at the end of string automatically.
sprintf(createpass, "%s%s", userpass, salt);

INJOY。