How to use inet_pton() with the mingw compiler?

I experienced a similar issue with inet_ntop.

You may need to set _WIN32_WINNT to a code representing the minimum supported Windows version. That enables the APIs that are only supported in the more recent versions of Windows. MSVC does this for you, MinGW does not, but it is easy to fix.

So for example if you wanted to support Windows 7+, #define _WIN32_WINNT 0x0601

---

Consult https://learn.microsoft.com/en-us/cpp/porting/modifying-winver-and-win32-winnt

//
// _WIN32_WINNT version constants
//
#define _WIN32_WINNT_NT4                    0x0400 // Windows NT 4.0
#define _WIN32_WINNT_WIN2K                  0x0500 // Windows 2000
#define _WIN32_WINNT_WINXP                  0x0501 // Windows XP
#define _WIN32_WINNT_WS03                   0x0502 // Windows Server 2003
#define _WIN32_WINNT_WIN6                   0x0600 // Windows Vista
#define _WIN32_WINNT_VISTA                  0x0600 // Windows Vista
#define _WIN32_WINNT_WS08                   0x0600 // Windows Server 2008
#define _WIN32_WINNT_LONGHORN               0x0600 // Windows Vista
#define _WIN32_WINNT_WIN7                   0x0601 // Windows 7
#define _WIN32_WINNT_WIN8                   0x0602 // Windows 8
#define _WIN32_WINNT_WINBLUE                0x0603 // Windows 8.1
#define _WIN32_WINNT_WINTHRESHOLD           0x0A00 // Windows 10
#define _WIN32_WINNT_WIN10                  0x0A00 // Windows 10

Author: Paul Vixie, 1996. Tested in MinGW/GCC:

int inet_pton(int af, const char *src, char *dst)
{
    switch (af)
    {
    case AF_INET:
        return inet_pton4(src, dst);
    case AF_INET6:
        return inet_pton6(src, dst);
    default:
        return -1;
    }
}

..

#define NS_INADDRSZ  4
#define NS_IN6ADDRSZ 16
#define NS_INT16SZ   2

..

int inet_pton4(const char *src, char *dst)
{
    uint8_t tmp[NS_INADDRSZ], *tp;

    int saw_digit = 0;
    int octets = 0;
    *(tp = tmp) = 0;

    int ch;
    while ((ch = *src++) != '\0')
    {
        if (ch >= '0' && ch <= '9')
        {
            uint32_t n = *tp * 10 + (ch - '0');

            if (saw_digit && *tp == 0)
                return 0;

            if (n > 255)
                return 0;

            *tp = n;
            if (!saw_digit)
            {
                if (++octets > 4)
                    return 0;
                saw_digit = 1;
            }
        }
        else if (ch == '.' && saw_digit)
        {
            if (octets == 4)
                return 0;
            *++tp = 0;
            saw_digit = 0;
        }
        else
            return 0;
    }
    if (octets < 4)
        return 0;

    memcpy(dst, tmp, NS_INADDRSZ);

    return 1;
}

...

int inet_pton6(const char *src, char *dst)
{
    static const char xdigits[] = "0123456789abcdef";
    uint8_t tmp[NS_IN6ADDRSZ];

    uint8_t *tp = (uint8_t*) memset(tmp, '\0', NS_IN6ADDRSZ);
    uint8_t *endp = tp + NS_IN6ADDRSZ;
    uint8_t *colonp = NULL;

    /* Leading :: requires some special handling. */
    if (*src == ':')
    {
        if (*++src != ':')
            return 0;
    }

    const char *curtok = src;
    int saw_xdigit = 0;
    uint32_t val = 0;
    int ch;
    while ((ch = tolower(*src++)) != '\0')
    {
        const char *pch = strchr(xdigits, ch);
        if (pch != NULL)
        {
            val <<= 4;
            val |= (pch - xdigits);
            if (val > 0xffff)
                return 0;
            saw_xdigit = 1;
            continue;
        }
        if (ch == ':')
        {
            curtok = src;
            if (!saw_xdigit)
            {
                if (colonp)
                    return 0;
                colonp = tp;
                continue;
            }
            else if (*src == '\0')
            {
                return 0;
            }
            if (tp + NS_INT16SZ > endp)
                return 0;
            *tp++ = (uint8_t) (val >> 8) & 0xff;
            *tp++ = (uint8_t) val & 0xff;
            saw_xdigit = 0;
            val = 0;
            continue;
        }
        if (ch == '.' && ((tp + NS_INADDRSZ) <= endp) &&
                inet_pton4(curtok, (char*) tp) > 0)
        {
            tp += NS_INADDRSZ;
            saw_xdigit = 0;
            break; /* '\0' was seen by inet_pton4(). */
        }
        return 0;
    }
    if (saw_xdigit)
    {
        if (tp + NS_INT16SZ > endp)
            return 0;
        *tp++ = (uint8_t) (val >> 8) & 0xff;
        *tp++ = (uint8_t) val & 0xff;
    }
    if (colonp != NULL)
    {
        /*
         * Since some memmove()'s erroneously fail to handle
         * overlapping regions, we'll do the shift by hand.
         */
        const int n = tp - colonp;

        if (tp == endp)
            return 0;

        for (int i = 1; i <= n; i++)
        {
            endp[-i] = colonp[n - i];
            colonp[n - i] = 0;
        }
        tp = endp;
    }
    if (tp != endp)
        return 0;

    memcpy(dst, tmp, NS_IN6ADDRSZ);

    return 1;
}