prevent用户传递负数的函数接受无符号整型 [英] Prevent user passing negative numbers to a function accepting unsigned int

问题描述

因此​​，这里的code：

So here's the code:

int create_mask(unsigned b, unsigned e)
{
  unsigned int mask=1;

  if(b<e || b<0 || e<0)
  {
    printf("Wrong values, starting bit can't be smaller than ending.\n");
    printf("Both got to be >= 0.\n");
    exit(EXIT_FAILURE);
  }
  while(b>0)
  {
    printf("%u\n", b);
    mask<<=1;
    if(b>e)
      mask|=1;
    b--;
  }

  return ~mask; /* negates mask for later purpose that is clearing corresponding bits */
}

函数一些位运算创建掩模，但应考虑两个无符号整数b和e，两个非负。问题是如何$负数的对$ pvent用户输入？
当调用函数时使用（-1,0）就开始循环，并与错误shoult退出。

Function creates mask for some bit operations, but should take two unsigned ints b and e, both non-negative. Question is how to prevent user input of negative numbers? When function is called with (-1,0) it start the loop, and shoult exit with error.

推荐答案

您可以只输入一个字符串，检查它是否包含 - 字符，并产生一个如果它的错误。否则你将其转换为一个无符号整数，然后继续上。 （作为那么字符串 strtoul将（）转换阅读是pferred比使用 scanf（）的反正$ P $，特别是而你不知道所有的怪癖的 scanf（）的）

You could just input a string, check if it contains a '-' character, and yield an error if it does. Else you convert it to an unsigned integer and proceed on. (Reading as a string then converting with strtoul() is preferred over using scanf() anyway, especially while you aren't aware of all of the quirks of scanf().)

char buf[LINE_MAX];
fgets(buf, sizeof buf, stdin);

if (strchr(buf, '-') != NULL) {
    fprintf(stderr, "input must be non-negative!\n");
    exit(-1);
}

unsigned int n = strtoul(buf, NULL, 0);

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