c - 密码生成器显示池中未出现的标志

Question

我编写了一个密码生成器，但它有时似乎表现得很笨拙。当我启动程序时，有时会得到如下输出:

password: pyi>Sx2Z

我实际上排除了“大于”字符。我什至打印了池中的每个可用字符，并且没有出现“大于”字符。我有一点困惑。我感谢任何帮助或解释。提前致谢。这是我的代码:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define STARTNUMBER     '0'
#define ENDNUMBER       '9'
#define STARTUPLETTER   'A'
#define ENDUPLETTER     'z'
#define STARTLOWLETTER  'a'
#define ENDLOWLETTER    'z'
#define SIZE            (2*26+10)
#define DEBUG

int main(int argc, char** argv)
{
  srand(time(0));
  int defaultLenght = 8;
  if(argc == 2)
  {
    defaultLenght = atoi(argv[1]);
  }
  char pool[SIZE];
  char password[defaultLenght];
  char digitCount = ENDNUMBER - STARTNUMBER + 1;
  for(int c = 0; c < digitCount; c++)
  {
    pool[c] = STARTNUMBER + c;
  }
  char upLetterCount = ENDLOWLETTER - STARTUPLETTER + 1;
  for(int c = 0; c < upLetterCount; c++)
  {
    pool[digitCount + c] = STARTUPLETTER + c;
  }
  char lowLetterCount = ENDLOWLETTER - STARTLOWLETTER + 1;
  for(int c = 0; c < lowLetterCount; c++)
  {
    pool[digitCount + lowLetterCount + c] = STARTLOWLETTER + c;
  }
#ifdef DEBUG
  for(int i = 0; i < SIZE; i++)
  {
    printf("%c", pool[i]);;
  }
  printf("\r\n");
#endif
  printf("password: ");
  for(int i = 0; i < defaultLenght; i++)
  {
    int index = rand() % SIZE + 1;
    password[i] = pool[index];
    pool[index] = pool[SIZE -i -1];
    putchar(password[i]);
  }
  printf("\r\n");
  return(0);
}

Answer 1

使用随机索引选择入池有错误

int index = rand() % SIZE + 1;

它给出了 1..SIZE 范围内的数字，但池需要 0..(SIZE-1) 范围内的索引。这可能会导致选择数组之外的下一个字符。所以那一行应该是

int index = rand() % SIZE;

但是您的密码选择还有一个问题。您用池数组中的另一个字符覆盖所选字符，大概是为了防止它被选中两次，但您没有减小池的大小。我建议这样做:

int poolsize = SIZE;
for(int i = 0; i < defaultLenght; i++)
{
    int index = rand() % poolsize;
    password[i] = pool[index];
    pool[index] = pool[--poolsize];
    putchar(password[i]);
}