C IP 大整数和字符串相互转换

原理很简单，大整数转字符串就是一直对256取余，取整

字符串转大整数就是一直乘256

#include <stdio.h>
#include <string.h>
void swapStr(char *str, int left, int right) {
  int temp;
  for (; left <= right; left++, right--) {
    temp = str[left];
    str[left] = str[right];
    str[right] = temp;
  }
}
void iptostr(unsigned int ipint) { //大整数IP转字符串IP
  char ipstr[15] = {0};
  // printf("[ipstr] : %s\n", ipstr);
  char temp[4];
  int begin, end, len, cur;
  while (ipint) {
    // puts("------------------");
    cur = ipint % 256;
    sprintf(temp, "%d", cur);
    // printf("[temp] : %s\n", temp);
    strcat(ipstr, temp);
    // printf("[ipstr] : %s\n", ipstr);
    ipint /= 256;
    // printf("[ipint] : %d\n", ipint);
    if (ipint) {
      strcat(ipstr, ".");
      // printf("[ipstr] : %s\n", ipstr);
    }
  }
  len = strlen(ipstr);
  swapStr(ipstr, 0, len - 1);
  for (begin = 0, end = 0; end < len; end++, begin = end) {
    while (end < len && ipstr[end] != '.')
      end++;
    swapStr(ipstr, begin, end - 1);
  }

  puts(ipstr);
  return;
}
uint ipTint(char *ipstr) //字符串转整形
{
  if (ipstr == NULL)
    return 0;

  char *temp = NULL;
  uint i = 3, total = 0, cur;

  temp = strtok(ipstr, ".");

  while (temp != NULL) {
    cur = atoi(temp);
    if (cur >= 0 && cur <= 255) {
      total += cur * pow(256, i);
    }
    i--;
    temp = strtok(NULL, ".");
  }
  return total;
}

int main(void) {
  unsigned int ipint;
  scanf("%d", &ipint);
  iptostr(ipint);
}