C and C++ ip address and int type conversion example details

C/C++ ip address and int type conversion example details

preface

I recently read an interview question, which basically means to convert an ip address, such as "192.168.1.116", to an int address and back again

Train of thought

ip address to int type, for example, ip is "192.168.1.116", which is equivalent to ". "the ip address is divided into 4 parts, and the corresponding weight of each part is 256^3, 256^2, 256, 1, and they can be matched each other

int type to ip address, the idea is similar, can be divided by the weight, but there is a part of the string operation

The implementation code

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <math.h> 
 
#define LEN 16 
 
typedef unsigned int uint; 
 
/** 
 *  String transposition  
 */ 
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; 
} 
 
/** 
 *  Inverse string  
 */ 
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]; 
    } 
  } 
} 
 
/** 
 *  Turn the plastic ip string  
 */ 
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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