IP地址字符串和DWORD互转（VC）

转自：http://blog.sina.com.cn/s/blog_7d0544020100xjd7.html

#include <windows.h>

BOOL StrAddr2Dword(CHAR* lpStrAddr, DWORD* pdwAddr)

{

    char* lpPos = lpStrAddr;   //指向当前操作的字符

    int nNumCount = 0;         //数字的个数

    int nPointCount = 0;       //分隔点的个数

    BOOL bResult = FALSE;      //函数是否执行成功

    DWORD dwAddr = 0;

    DWORD Temp = 0;

    //进行参数的有效性检查

    if (!lpStrAddr || !pdwAddr)

    {

        return bResult;

    }

    while (*lpPos && nPointCount < 4)

    {

        if (nNumCount < 3)

        {

            if (*lpPos >= 0x30 &&  *lpPos <= 0x39)

            {

                bResult = TRUE;

                dwAddr -= Temp;    

                Temp *= 10;

                Temp += (*lpPos - 0x30);

                if (Temp & ~0xFF)

                {

                    break;  //从这里退出说明单个数超过了255,

                }

                dwAddr += Temp;

                nNumCount++;

            }

            else if (*lpPos != '.')

            {

                break;   //从这里退出说明有非数字的字符

            }

            else

            {

                if (!nNumCount)

                {

                    break;  //从这里退出说明单个数超过了255,或者是在一个分组中第个字符为点

                }

                else

                {

                    bResult = FALSE;

                    Temp = 0;

                    dwAddr <<= 8;

                    nNumCount = 0;

                    nPointCount++;

                }

            }

        }

        else

        {

            if (*lpPos != '.')

            {

                break;    //单组数字字符超过了3个

            }

            else

            {

                bResult = FALSE;

                Temp = 0;

                dwAddr <<= 8;

                nNumCount = 0;

                nPointCount++;

            }

        }

        lpPos++;

    }

    //凡是通过break跳出来的*lpPos肯定不为空。

    //bResult为假说明点以后再没取到字符。

    if (!(*lpPos) && nPointCount == 3 && bResult)

    {

        *pdwAddr = dwAddr;

    }

    else

    {

        bResult = FALSE;

    }

    return bResult;

}

BOOL DwordAddr2Str(DWORD dwAddr, CHAR* lpStrAddr)

{

    DWORD Fmt = 0xFF << 24;   //该运算为常量运算编译器会做优化

    DWORD Temp = 0;

    CHAR Number = 0;

    if (!lpStrAddr)

    {

        return FALSE;

    }

    for (int i = 3; i >= 0; i--)

    {

        Temp = dwAddr & Fmt;

        Temp >>= 8*i;

        Number = (BYTE)Temp/100;

        if (Number != 0)

        {

            *lpStrAddr = Number + '0';

            lpStrAddr++;

        }

        Number = ((BYTE)Temp/10) % 10;

        if (Number != 0)

        {

            *lpStrAddr = Number + '0';

            lpStrAddr++;

        }

        Number = (BYTE)Temp;

        *lpStrAddr = Number + '0';

        lpStrAddr++;

        if (i > 0)

        {

            *lpStrAddr = '.';

            lpStrAddr++;

        }

        Fmt >>= 8;

}

    return TRUE;

}

//000.000.000.000是有效的IP

//0000.0000.0000.0000是无效的IP

//单组长度只支持到3位。

int _tmain(int argc, _TCHAR* argv[])

{

    DWORD addr = 0;

    static char Buffer[1024*1024];

    do 

    {

        printf("请输入一个字符串形式的IP地址进行计算：");

        scanf("%s", Buffer);

        if (StrAddr2Dword(Buffer, &addr))

        {

            printf("\r\n%s = X\r\n", Buffer, addr);

            memset(Buffer, 0, sizeof(Buffer));

            printf("再次转回去\r\n");

            if (DwordAddr2Str(addr,Buffer))

            {

                printf("X = %s\r\n", addr, Buffer);

            }

            else

            {

                printf("转换失败！\r\n");

            }

        }

        else

        {

            printf("\r\n%s是无效的IP地址！\r\n", Buffer);

        }

    } while (TRUE);

    return 0;

}