IP address to integer

        IP Address to integer ： such as "192.168.1.254", Split by point , take 192 168 1 254 Save in a int a[4] In the array , And then through unsigned int nResult = (a[3] << 24) + (a[2] << 16) + (a[1] << 8) + a[0] Get an unsigned 32 An integer .

         Convert integer to IP Address ： Convert this integer to an unsigned integer 32 Bit binary number . From left to right , Divide every eight bits , obtain 4 paragraph 8 The binary number of bits , Convert these binary numbers to integers

#include <iostream>
#include <string>

using namespace std;

unsigned int IPToValue(const string& strIP)//IP Convert to integer 
{
    //IP Convert to numeric 
    // No format check 
    // The return value is the result 

    int a[4];
    string IP = strIP;
    string strTemp;
    size_t pos;
    size_t i = 3;

    do
    {
        pos = IP.find(".");

        if (pos != string::npos)
        {
            strTemp = IP.substr(0, pos);
            a[i] = atoi(strTemp.c_str());//int atoi(const char *str);
            i--;
            IP.erase(0, pos + 1);// From the position 0 To delete pos+1 Characters 
        }
        else
        {
            strTemp = IP;
            a[i] = atoi(strTemp.c_str());
            break;
        }

    } while (1);

    unsigned int nResult = (a[3] << 24) + (a[2] << 16) + (a[1] << 8) + a[0];
    return nResult;
}

string ValueToIP(const int& nValue)// Convert integer to ip
{
    // The value is converted to IP
    // No format check 
    // The return value is the result 

    char strTemp[20];
    sprintf(strTemp, "%d.%d.%d.%d",
    (nValue & 0xff000000) >> 24,
    (nValue & 0x00ff0000) >> 16,
    (nValue & 0x0000ff00) >> 8,
    (nValue & 0x000000ff));

    return string(strTemp);
}

int main()
{
    string strIP = "192.168.1.254";
    cout << IPToValue(strIP) << endl;

    cout << ValueToIP(3232236030) << endl;

    return 0;
}