求linux的ip地址

#include 
#include 
#include 

int main()
{
    system("ifconfig > ip_info");

    FILE* fp = fopen("ip_info","r");

    //求文件大小
    int file_size;
    fseek(fp,0,SEEK_END);
    file_size = ftell(fp);
    rewind(fp);

    //申请空间
    char* ip_info = malloc(file_size+1);//'\0'
    memset(ip_info,0,file_size+1);//清零，制造结束符

    fread(ip_info,1,file_size,fp);//文件读入文件ip

    // 查找子字符串   
    char* p = strstr(ip_info,"inet addr:");
    char ip[16];   
    //网络ip:四段点分式,四个字节存储,或者16个字符
    if(NULL == p)
    {
        fprintf(stderr,"网络配置异常！\n");
    }
    else
    {
        p += strlen("inet addr:");   
        sscanf(p,"%s",ip);//串io
        printf("inet addr:%s\n",ip);
    }

    free(ip_info);

    fclose(fp);

    system("rm -rf ip_info");   

    return 0;
}