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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