How to convert string to IP address and vice versa

Question

how can I convert a string ipAddress (struct in_addr) and vice versa? and how do I turn in unsigned long ipAddress? thanks

Solution 1

Use inet_ntop() and inet_pton() if you need it other way around. Do not use inet_ntoa(), inet_aton() and similar as they are deprecated and don't support ipv6.

Here is a nice guide with quite a few examples.

// IPv4 demo of inet_ntop() and inet_pton()

struct sockaddr_in sa;
char str[INET_ADDRSTRLEN];

// store this IP address in sa:
inet_pton(AF_INET, "192.0.2.33", &(sa.sin_addr));

// now get it back and print it
inet_ntop(AF_INET, &(sa.sin_addr), str, INET_ADDRSTRLEN);

printf("%s\n", str); // prints "192.0.2.33"

Solution 2

I'm not sure if I understood the question properly.

Anyway, are you looking for this:

std::string ip ="192.168.1.54";
std::stringstream s(ip);
int a,b,c,d; //to store the 4 ints
char ch; //to temporarily store the '.'
s >> a >> ch >> b >> ch >> c >> ch >> d;
std::cout << a << "  " << b << "  " << c << "  "<< d;

Output:

192  168  1  54

Solution 3

I was able to convert string to DWORD and back with this code:

char strAddr[] = "127.0.0.1"
DWORD ip = inet_addr(strAddr); // ip contains 16777343 [0x0100007f in hex]

struct in_addr paddr;
paddr.S_un.S_addr = ip;

char *strAdd2 = inet_ntoa(paddr); // strAdd2 contains the same string as strAdd

I am working in a maintenance project of old MFC code, so converting deprecated functions calls is not applicable.

Solution 4

inet_ntoa() converts a in_addr to string:

The inet_ntoa function converts an (Ipv4) Internet network address into an ASCII string in Internet standard dotted-decimal format.

inet_addr() does the reverse job

The inet_addr function converts a string containing an IPv4 dotted-decimal address into a proper address for the IN_ADDR structure

PS this the first result googling "in_addr to string"!

Solution 5

To convert string to in-addr:

in_addr maskAddr;
inet_aton(netMaskStr, &maskAddr);

To convert in_addr to string:

char saddr[INET_ADDRSTRLEN];
inet_ntop(AF_INET, &inaddr, saddr, INET_ADDRSTRLEN);

View more solutions

Comments

[Milan]

Those functions are deprecated and should not be used.

[CharlesB]

@Milan OK. Though the OP uses in_addr struct that deal with ipv4

[Safari]

What should I do to use them under Windows? What should I include?

[Safari]

What should I do to use them under Windows? What should I include?

[Milan]

If using winsock then InetNtop and InetPton on windows vista and later. Header file Ws2tcpip.h . A tip is to look at examples on msdn.

[CharlesB]

The answer is in the function's documentation, (follow the link): include Winsock2.h.

[Milan]

WSAAddressToString (ntop) and WSAStringToAddress (pton) in Winsock2.h. I would suggest an upgrade to at least vista, and to ask you that next time you specify what platform you are developing when asking questions :)

[Carcigenicate]

@Milan Thanks! Everywhere says to use the inet prefix functions, but only 1 of them is included in Winsock2.

[Remy Lebeau]

There is also RtlIpv(4|6)AddressToString/Ex() and RtlIpv(4|6)StringToAddress/Ex() functions

[martian]

This link is not available any more

[Qi Fan]

What do "p" and "n" mean in these functions? If I know the meanings I can probably remember them better.

[JustWe]

What about IPv6?

[Marked as Duplicate]

@QiFan The "n" stands for "network", and the "p" for "(text) presentation".

[Luk]

@Milan: Hey, do you know if there is a function to achieve exactly the same, but that allows for a name as src-string instead of the IP address in dotted decimal form? I want to give a name that can be resolved by my DNS server instead

[Alexis]

adding the header would have been nice too

[Cerin]

This doesn't work. localhost resolves to arbitrary IPs that have nothing to do with my actual IP.

[mercury]

I am wondering why all languages consider ip as a string than a 32 bit integer?