c - Parse network 'interfaces' for read/write using pointer as parameter of functions -


i write small program read /etc/network/interfaces, save *ethernet_t[], change value, , write interfaces. works fine in main function. can not separate code function , pass pointer of array that. following code:

#include <stdio.h> #include <ctype.h>  typedef struct {   char sys_ifname[10];   char address[20];   char netmask[20];   char network[20];   char gateway[20];   protocol_e protocol; } ethernet_t;  #define max_nic 4  char *removing_leading_and_trailing_whitespace(char *a);  int write_to_interface (ethernet_t *interface[], const char *filename) {   file *fp;    /* should grant root privilege */   if ((fp = fopen(filename, "w")) == null) {     perror ("fopen");     exit (-1);   }   printf ("file open %s writing successfully\n", filename);    /* set dhcp test */   interface[2]->protocol = dhcp;    fprintf (fp, "# /etc/network/interface\n");    fprintf (fp, "\nauto lo\n");   fprintf (fp, "iface lo inet loopback\n");    int i;   (i=0; i<max_nic; i++) {     printf ("\nauto %s\n", interface[i]->sys_ifname);      fprintf (fp, "\nauto %s\n", interface[i]->sys_ifname);     fprintf (fp, "iface %s inet %s\n", interface[i]->sys_ifname,             interface[i]->protocol == dhcp ? "dhcp" : "static");     if (interface[i]->protocol == static) {         fprintf (fp, "\taddress %s\n", interface[i]->address);         fprintf (fp, "\tnetmaks %s\n", interface[i]->netmask);         fprintf (fp, "\tnetwork %s\n", interface[i]->network);         fprintf (fp, "\tgateway %s\n", interface[i]->gateway);     }   }    fclose(fp);   printf ("done!\n");   return 0; }  int main(void) {   int i;   char line[256];   char *p;   file *fp;   ethernet_t interface[max_nic];   ethernet_t *current_interface = null;    bzero(interface, sizeof(ethernet_t) * max_nic);  #if yocto   const char *filename = "/etc/network/interfaces"; #else   const char *filename = "/etc/network/interfaces.ubuntu"; #endif    if ((fp = fopen(filename, "r")) == null) {     perror ("fopen");     exit (-1);   }    = 0;   current_interface = interface;    while (fgets(line, sizeof(line), fp) && <= max_nic) {     p = removing_leading_and_trailing_whitespace(line);     if (strlen(p) && p[0] != '#') {         /* scan interface name */         if (strstr(p, "auto")) {             p = removing_leading_and_trailing_whitespace(p + strlen("auto"));             if (strcmp(p, "lo") != 0) { /* interface lo loopback */                 current_interface = interface + i;                 /* interface default static */                 current_interface->protocol = static;                 strcpy (current_interface->sys_ifname, p);                 i++;             }         }         else if (strstr(p, "dhcp") && current_interface) {             current_interface->protocol = dhcp;         }         else if (strstr(p, "address") && current_interface) {             p = removing_leading_and_trailing_whitespace(p + strlen("address"));             memcpy (current_interface->address, p, strlen(p));         }         else if (strstr(p, "netmask") && current_interface) {             p = removing_leading_and_trailing_whitespace(p + strlen("netmask"));             memcpy (current_interface->netmask, p, strlen(p));         }         else if (strstr(p, "network") && current_interface) {             p = removing_leading_and_trailing_whitespace(p + strlen("network"));             memcpy (current_interface->network, p, strlen(p));         }         else if (strstr(p, "gateway") && current_interface) {             p = removing_leading_and_trailing_whitespace(p + strlen("gateway"));             memcpy (current_interface->gateway, p, strlen(p));         }     } /* if (strlen(p) && p[0] != '#') */   } /* while */    fclose (fp);  #if 1   write_to_interface ((ethernet_t **)interface, filename); #else   /* should grant root privilege */   if ((fp = fopen(filename, "w")) == null) {     perror ("fopen");     exit (-1);   }   printf ("file open %s writing successfully\n", filename);    interface[2].protocol = dhcp;    fprintf (fp, "# /etc/network/interface\n");   fprintf (fp, "# auto generated vicom\n");    fprintf (fp, "\nauto lo\n");   fprintf (fp, "iface lo inet loopback\n");    (i=0; i<max_nic; i++) {     fprintf (fp, "\nauto %s\n", interface[i].sys_ifname);     fprintf (fp, "iface %s inet %s\n", interface[i].sys_ifname,             interface[i].protocol == dhcp ? "dhcp" : "static");     if (interface[i].protocol == static) {         fprintf (fp, "\taddress %s\n", interface[i].address);         fprintf (fp, "\tnetmaks %s\n", interface[i].netmask);         fprintf (fp, "\tnetwork %s\n", interface[i].network);         fprintf (fp, "\tgateway %s\n", interface[i].gateway);     }   }    fclose(fp);   printf ("done!\n"); #endif    return 0; }

when run in linux, got

file open /etc/network/interfaces.ubuntu writing segmentation fault (core dumped)

my question how dereference pointer of array in function properly?

thank you, some-programmer-dude , storyteller. follow hint, rewrite code bellow:

int write_to_interface (ethernet_t *interface, const char *filename) {   file *fp;    /* should grant root privilege */   if ((fp = fopen(filename, "w")) == null) {     perror ("fopen");     exit (-1);   }   printf ("file open %s writing successfully\n", filename); #if 0   (interface + 2)->protocol = dhcp; #endif   fprintf (fp, "# /etc/network/interface\n");   fprintf (fp, "\nauto lo\n");   fprintf (fp, "iface lo inet loopback\n");    int i;   (i=0; i<max_nic; i++) {     fprintf (fp, "\nauto %s\n", (interface+i)->sys_ifname);     fprintf (fp, "\nauto %s\n", (interface+i)->sys_ifname);     fprintf (fp, "iface %s inet %s\n", (interface+i)->sys_ifname,             (interface+i)->protocol == dhcp ? "dhcp" : "static");     if ((interface+i)->protocol == static) {       fprintf (fp, "\taddress %s\n", (interface+i)->address);       fprintf (fp, "\tnetmaks %s\n", (interface+i)->netmask);       fprintf (fp, "\tnetwork %s\n", (interface+i)->network);       fprintf (fp, "\tgateway %s\n", (interface+i)->gateway);     }   }    fclose(fp);   printf ("done!\n");    return 0; }

thank both! save life.


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