C/C++ ip地址与int类型的转换实例详解

C/C++ ip地址与int类型的转换实例详解

前言

最近看道一个面试题目，大体意思就是将ip地址，例如“192.168.1.116”转换成int类型，同时还能在转换回去

思路

ip地址转int类型，例如ip为“192.168.1.116”,相当于“.“将ip地址分为了4部分，各部分对应的权值为256^3, 256^2, 256, 1,相成即可

int类型转ip地址，思路类似，除以权值即可，但是有部分字符串的操作

实现代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#define LEN 16

typedef unsigned int uint;

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

  char *token;
  uint i = 3, total = 0, cur;

  token = strtok(ipstr, ".");

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

  return total;
}

/**
 * 逆置字符串
 */
void swapStr(char *str, int begin, int end)
{
  int i, j;

  for (i = begin, j = end; i <= j; i ++, j --) {
    if (str[i] != str[j]) {
      str[i] = str[i] ^ str[j];
      str[j] = str[i] ^ str[j];
      str[i] = str[i] ^ str[j];
    }
  }
}

/**
 * 整形转ip字符串
 */
char* ipTstr(uint ipint)
{
  char *new = (char *)malloc(LEN);
  memset(new, '\0', LEN);
  new[0] = '.';
  char token[4];
  int bt, ed, len, cur;

  while (ipint) {
    cur = ipint % 256;
    sprintf(token, "%d", cur);
    strcat(new, token);
    ipint /= 256;
    if (ipint) strcat(new, ".");
  }

  len = strlen(new);
  swapStr(new, 0, len - 1);

  for (bt = ed = 0; ed < len;) {
    while (ed < len && new[ed] != '.') {
      ed ++;
    }
    swapStr(new, bt, ed - 1);
    ed += 1;
    bt = ed;
  }

  new[len - 1] = '\0';

  return new;
}

int main(void)
{
  char ipstr[LEN], *new;
  uint ipint;

  while (scanf("%s", ipstr) != EOF) {
    ipint = ipTint(ipstr);
    printf("%u\n", ipint);

    new = ipTstr(ipint);
    printf("%s\n", new);
  }

  return 0;
}

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