Convert IP for reverse ip lookup

Question

I have an IP address, for example. char *ip = "192.168.1.13" and you need to convert it to this "13.1.168.192" Is there any possibility in C for this already, or should I do it myself just by making tokens and reconnecting them?

Answer 1

You can always use inet_pton to convert it to binary form, which will simplify the inverse conversion, and then convert back to text using inet_ntop .

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Remember that an IPv4 address is only a 32-bit unsigned integer. Swapping bytes around this is very easy.

Something like that:

 const char ip[] = "192.168.0.1"; char reversed_ip[INET_ADDRSTRLEN]; in_addr_t addr; /* Get the textual address into binary format */ inet_pton(AF_INET, ip, &addr); /* Reverse the bytes in the binary address */ addr = ((addr & 0xff000000) >> 24) | ((addr & 0x00ff0000) >> 8) | ((addr & 0x0000ff00) << 8) | ((addr & 0x000000ff) << 24); /* And lastly get a textual representation back again */ inet_ntop(AF_INET, &addr, reversed_ip, sizeof(reversed_ip)); 

After this code, the reversed_ip variable contains the revered address as a string.

Answer 2

 int a,b,c,d; char *ip = "192.168.1.13" char ip2[16]; sscanf(ip,"%d.%d.%d.%d",&a,&b,&c,&d); sprintf(ip2, "%d.%d.%d.%d", d, c, b, a); 

Answer 3

 #include <stdio.h> #include <string.h> void swap(char *a, char *b){ char wk = *a; *a = *b; *b = wk; } void strpartrev(char *s, int len){ int i,j; for(i=0,j=len-1; i<len/2 ;++i,--j) swap(s + i, s + j); } char *strwordrev(char *str, char delimiter){ //str change destructively int sp = -1, wordlen=0; char stack[16], *p=str; while(*p){ if(*p == delimiter){ strpartrev(stack + sp - wordlen + 1, wordlen); wordlen = 0; } else { ++wordlen; } stack[++sp] = *p++; } strpartrev(stack + sp - wordlen + 1 , wordlen); p = str; do{ *p++ = stack[sp--]; }while(sp>=0); return str; } char *strWordRev(char *str, char delimiter){ //str change destructively char *head, *tail; int len = strlen(str); head = str; while(tail = strchr(head, delimiter)){ strpartrev(head, tail - head); head = tail + 1; } strpartrev(head, str + len - head); strpartrev(str, len); return str; } int main(void){ char *ip = "192.168.1.13"; char rip[16]; strcpy(rip, ip); printf("%s\n", strWordRev(rip, '.'));//13.1.168.192 return 0; } 

Answer 4

Separate ip into an array and use the code to modify the array.

here is a neat reverse bit of code code that I found here: http://www.programmingsimplified.com/c-program-reverse-array

 #include <stdio.h> int main() { int n, c, d, a[100], b[100]; printf("Enter the number of elements in array\n"); scanf("%d", &n); printf("Enter the array elements\n"); for (c = 0; c < n ; c++) scanf("%d", &a[c]); /* * Copying elements into array b starting from end of array a */ for (c = n - 1, d = 0; c >= 0; c--, d++) b[d] = a[c]; /* * Copying reversed array into original. * Here we are modifying original array, this is optional. */ for (c = 0; c < n; c++) a[c] = b[c]; printf("Reverse array is\n"); for (c = 0; c < n; c++) printf("%d\n", a[c]); return 0; } 

Answer 5

You can convert a string to addrinfo using getaddrinfo . Set AI_NUMERICHOST to prevent DNS lookups.

 addrinfo hint; memset(&hint, 0, sizeof(addrinfo)); hint.ai_socktype = SOCK_STREAM; hint.ai_protocol = IPPROTO_TCP; hint.ai_family = AF_INET; hint.ai_flags = AI_NUMERICHOST; // prevents dns lookup addrinfo *result = nullptr; if (getaddrinfo(name, nullptr, &hint, &result)) return false; uint32_t ip; memcpy(&ip, &result, sizeof(uint32_t)); uint32_t ipreversed = htonl(ip); freeaddrinfo(result);