IP地址的读取 LINUX C

#include <stdio.h>
#include <string.h>

FILE *fp = NULL;
#define NETWORK_FILE "/etc/network/interfaces"

static char* getNetworkInfo(char *maches)
{
    char szBuf[64];
    char *szNetwork=NULL;
    int i = 0;
    if((fp=fopen(NETWORK_FILE, "r"))==NULL)             //判断文件是否为空
    {
        printf( "Can 't   open   file!\n"); 
        return 0;
    }
    while(fgets(szBuf,128,fp))                         //从文件开关开始向下读，把读到的内容放到szBuf中
    {                         
        if(strstr(szBuf,maches) != NULL)                 //找到maches在文件中第一次出现的位置。。如address 
        {
            for(i =0;i < strlen(szBuf);i++)
          {              
                if(isdigit(*(szBuf+i)))                      //从szBuf字符串中找出数字。
                {
                    szNetwork = (char*)malloc(strlen(szBuf));  //为szNetwork分配内存
                    strcpy(szNetwork,szBuf+i);             
                    szNetwork[strlen(szNetwork)-1] = '\0';
                    fclose(fp);
                    return szNetwork;
                }
            }
        }else
            continue;
    }
    fclose(fp);
    return szNetwork;
}

int main()
{
    char *IPaddress;
    char *netmask;
    char *gateway;
    IPaddress = getNetworkInfo("address");               //找到 LINUX 配制文件中的 interfaces 文件 匹配IP 。然后读出来 
    netmask   = getNetworkInfo("netmask");               //子网掩码
    gateway   = getNetworkInfo("gateway");               //默认网关
    printf("IPaddress:%s\n",IPaddress);
    printf("netmask:%s\n",netmask);
    printf("gateway:%s\n",gateway);
}

/*****************************
 *    interfaces 里的内容    * 
 *                           *
*****************************/
/*****************************
iface lo inet loopback                      
auto eth0 
iface eth0 inet static
        address 192.168.1.139 
        netmask 255.255.255.0
        gateway 192.168.1.1
*****************************/

static void writeAddr(char addressbuf[255])                 //IP 写入
{
    FILE* fp=NULL;
    int i,Lid = -1; 
    char szBuf[128];
    char szTemp[128]; 
    char szTmp[20][256];
  memset(szTmp,0,sizeof(szTmp));
  memset(szBuf,0,sizeof(szBuf));
 
    if((fp=fopen(NETWORK_FILE, "r+"))==NULL) 
    { 
        printf( "setIP Can 't open file!\n"); 
        return;
    } 
    while(fgets(szBuf,256,fp)) 
    {
        Lid++;
         if('#' != *szBuf)
        {
            if(strstr(szBuf,"gateway") != NULL)
            {
                memset(szTemp,0,sizeof(szTemp));
                snprintf(szTemp, sizeof(szTemp), "\tgateway %s\n",addressbuf);
                strcpy(szTmp[Lid],szTemp);
            }else
                strcpy(szTmp[Lid],szBuf);
        }else{
            strcpy(szTmp[Lid],szBuf);
        }
    }
    fclose(fp);
    printf("%s\n",szTmp[6]);
    
    if((fp=fopen(NETWORK_FILE, "w"))==NULL) 
    { 
        printf( "writeIP Can 't open file!\n");
        return;
    }else{
         for(i = 0;i <=Lid;i++) 
            fputs(szTmp[i],fp);
        fclose(fp);
    }
    
    
    return;
}