题解 | #判断两个IP是否属于同一子网#

#include <stdio.h>

unsigned int AddressToInt(char str[])//地址转换成数字
{
    int ippart1,ippart2,ippart3,ippart4;
    ippart1=ippart2=ippart3=ippart4=-1;
    sscanf(str,"%d.%d.%d.%d",&ippart1,&ippart2,&ippart3,&ippart4);
    unsigned int b=(unsigned int)(ippart1<<24)+(unsigned int)(ippart2<<16)+(unsigned int)(ippart3<<8)+(unsigned int)ippart4;
    return b;
}
int IsIPAddress(char str[])//判断是否合法ip
{
    int flag=0;
    int ippart1,ippart2,ippart3,ippart4;
    ippart1=ippart2=ippart3=ippart4=-1;
    flag=sscanf(str,"%d.%d.%d.%d",&ippart1,&ippart2,&ippart3,&ippart4);
    if(flag!=4)
    {
        flag=0;
        return flag;
    }
    if(ippart1<0||ippart1>255||ippart2<0||ippart2>255||ippart3<0||ippart3>255||ippart4<0||ippart4>255)
    {
        flag=0;
        return flag;
    }
    else {
    flag=1;
    return flag;
    }
}

int IsSubnetMask(char str[])//判断是否合法掩码
{
    int flag=0;
    if(IsIPAddress(str))
    {
    int ippart1,ippart2,ippart3,ippart4;
    ippart1=ippart2=ippart3=ippart4=-1;
    sscanf(str,"%d.%d.%d.%d",&ippart1,&ippart2,&ippart3,&ippart4);
    unsigned int b=(unsigned int)(ippart1<<24)+(unsigned int)(ippart2<<16)+(unsigned int)(ippart3<<8)+(unsigned int)ippart4;
    b=~b+1;
    if((b&(b-1))==0)
    {
        flag=1;
    }
    }
    return flag;
}

int IsInSameSubnet(char str1[],char str2[],char str3[])//判断是否为同一子网
{
    int flag=0;
    if(IsSubnetMask(str1)&&IsIPAddress(str2)&&IsIPAddress(str3))
    {
        unsigned int b1=AddressToInt(str1);
        unsigned int b2=AddressToInt(str2);
        unsigned int b3=AddressToInt(str3);
        if((b1&b2)==(b1&b3))
        {
            flag=1;
        }
    }
    return flag;
}

int main() {
    char subnetMask[20]={0};
    char ipAddress1[20]={0};
    char ipAddress2[20]={0};
    scanf("%s",subnetMask);
   // getchar();
    scanf("%s",ipAddress1);
   // getchar();
    scanf("%s",ipAddress2);
   // getchar();
   int flag=-1;
   if((IsSubnetMask(subnetMask)==0)||(IsIPAddress(ipAddress1)==0)||(IsIPAddress(ipAddress2)==0))
   {
    flag=1;
   }
   else if(IsInSameSubnet(subnetMask,ipAddress1,ipAddress2))
   {
    flag=0;
   }
   else {
   flag=2;
   }
   printf("%d",flag);



   return 0;


}