为什么我在这个使用 malloc 的程序上会出错？

Question

一个加密明文的程序。 key 和 value 被传递给一个函数，function returns 一个指针。不确定为什么编译器会尖叫。

int main() {
  char *ciphertext = ciphering(key, plaintext);
  printf("ciphertext: %s\n", ciphertext);
  free(ciphertext);
}

char *ciphering(string key, string plaintext) {
  int n = strlen(plaintext);
  char *ciphertext = malloc(n + 1);

  // for loop fills in the cipher in ciphertext
  for (int i = 0; i < n; i++) {
    if (isupper(plaintext[i]))
      ciphertext[i] = toupper(key[(tolower(plaintext[i]) - 97)]);
    else if (islower(plaintext[i]))
      ciphertext[i] = tolower(key[(tolower(plaintext[i]) - 97)]);
    else
      ciphertext[i] = plaintext[i];
  }
  return ciphertext;
}

//==820==  Uninitialised value was created by a heap allocation

Answer 1

您忘记以 null 终止生成的字符串。

char *ciphertext = malloc(n + 1);
ciphertext[n] = '[=10=]';

为什么我在这个使用 malloc 的程序上会出错？

Why do I get an error on this program that uses malloc?

c

malloc

valgrind

pointers