Global Variables

Taka · 10-30-2007, 03:53 AM

If anyone could help me with the below feedback it would be great... I'm apparently not allowed to have Global Variables so I need to change my declarations but whenever I change them I seem to stuff my code up. Any help would be great.

21. FILE *fp;
==> Global variables are not allowed in this subject.

22. char *packet;
==> Global variables are not allowed in this subject.

23. struct messagenode *head_msg, *save_msg, *current_msg;
==> Global variables are not allowed in this subject.

24. struct pktnode *head_pkt, *save_pkt, *current_pkt;
==> Global variables are not allowed in this subject.

The previous lines in assign2.c are unacceptable

Code:

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

struct pktnode
{
        int pkt_id;
        char *message;
        struct pktnode *next;
};

struct messagenode
{
        int msg_id;
        int prefix_len;
        char id_prefix[3];
        struct pktnode *pkthead;
        struct messagenode *next;

};

FILE *fp;
char *packet;
struct messagenode *head_msg, *save_msg, *current_msg;
struct pktnode  *head_pkt, *save_pkt, *current_pkt;
#define DELIM ":"

void initiate(char *filename);
void populateInList(char *packet);
struct messagenode *getMsgNode();
struct pktnode *getPktNode();
struct messagenode *search_msg(int msg_id);
struct pktnode *search_pkt(int pkt_id);
void getPacketInfo(char *packet,  int *msg_id, int *pkt_id, char *message, int *prefix_len_msg);
void display();
void cleanUpAll();
void sortMsg();
int getlen(char *arg);

int main(int argc,  char **argv)
{
   /* Argument checking section */
   if(argc != 2)
   {
      printf("Please provide one message data file\n");
      return -1;
   }
   /* Perform necessary program initiation steps */
   initiate(argv[1]);

   /* Main Loop */
   while(1)
   {
      /* Grab packet from file */
      fgets(packet, 2001, fp);

      /* If no packet remaining or END packet received then stop processing */
      if(packet == NULL || !strcmp(packet, "END\n")|| !strcmp(packet, "END"))
         break;
      /* function to process and populate packet in linked list*/
      populateInList(packet);
   }
   /* Sort the message linked list,  i.e. the outer one */
   sortMsg();

   /* Display the list data structure */
   display();
   
   /* Post process routines. file close + freeing allocated memories */
   cleanUpAll();
   return 0;
}
void initiate(char *filename)
{
   
   head_msg = NULL;
   head_pkt = NULL;

   /* Opening packet data file */
        fp = fopen(filename, "r");
        if(fp == NULL)
        {
                printf("Unable to open %s\n", filename);
                exit(0);
        }
   packet = (char *)malloc(2000 * sizeof(char));
}
void populateInList(char *packet)
{
   int msg_id, pkt_id, prefix_len_msg;
   char *message;
   struct messagenode *tmp_message,  *loc;
   struct pktnode *tmp_packet,  *loc_pkt;;

   message = (char *)malloc(1500*sizeof(char));
   
   /* Get message id,  packet id and packet message from each packet string -
    * passed to function as argument.
     */   
   getPacketInfo(packet, &msg_id, &pkt_id, message, &prefix_len_msg);
   
   /* If packet belongs to an existing message,  find the message's location in message list.
     * If message not found the NULL will be returned,  otherwise location of message node
     * will be returned.
     *
     * First condition: loc != NULL i.e. message entry found in list.
     */
   if((loc = search_msg(msg_id)) != NULL)
   {
      /* Get a new packet node and populate it pkt_id and packet message.*/
      tmp_packet = getPktNode();
      tmp_packet->pkt_id = pkt_id;
      tmp_packet->message = message;

      /* Current packet head is the packet head of the current message.*/
      head_pkt = loc->pkthead;

      /* If current packet head is NULL then New packet will be the head packet.*/
      if(head_pkt == NULL)
         head_pkt = tmp_packet;
      else 
      {
         /* Otherwise,  find the location where the New packet will be inserted.
           * If location is the head packet and New packet id is less than the packet
           * id of located node then insert the New packet before located node.
           * Otherwise,  insert the New packet node after the located packet node.
           */
         loc_pkt = search_pkt(pkt_id);

         if(loc_pkt == head_pkt && pkt_id < loc_pkt->pkt_id)
         {
            tmp_packet->next = head_pkt;
            head_pkt = tmp_packet;
            loc->pkthead = head_pkt;
         }  
         else 
         {
            tmp_packet->next = loc_pkt->next;
            loc_pkt->next = tmp_packet;
         }
      }
   }
   else
   {
      /* Second condition: loc==NULL i.e. Message entry not found.
        * So,  (1)Create a new message node. (2)Create a new packet node corresponding
        * to the new message node. (3) Populate them accordingly. (4) Add the new message 
        * node into the message linked list,  i.e. the outer one.
        */
      tmp_message = getMsgNode();
      tmp_message->msg_id = msg_id;
      tmp_message->prefix_len = prefix_len_msg;
      tmp_message->next = NULL;
      tmp_message->pkthead = getPktNode();
      tmp_message->pkthead->pkt_id = pkt_id;
      tmp_message->pkthead->message = message;
      
      if(head_msg == NULL)
         head_msg = tmp_message;
      else 
      {
         current_msg = head_msg;
         while(current_msg != NULL)
         {
            save_msg = current_msg;
            current_msg = current_msg->next;
         }
         save_msg->next = tmp_message;
      }
   }
}

struct messagenode * getMsgNode()
{
   struct messagenode *tmp;
   tmp = (struct messagenode *)malloc(sizeof(struct messagenode));
   tmp->pkthead = NULL;
   return tmp;
}

struct pktnode * getPktNode()
{
   struct pktnode *tmp;
   tmp = (struct pktnode *)malloc(sizeof(struct pktnode));
   tmp->next = NULL;
   return tmp;
}

/* Function to search a message node in message linked list.
 * If messahe head is NULL return NULL i.e. message not found
 * Else move through list searching for the node.
 * .. If whole list is traversed in vain then return NULL i.e. message not found.
 * .. Else return the location of the found message node.*/

struct messagenode *search_msg(int msg_id)
{
   current_msg = head_msg;
   if(head_msg == NULL)
      return NULL;
   else 
   {
      while((current_msg != NULL) && (current_msg->msg_id != msg_id))
         current_msg = current_msg->next;
         if(current_msg == NULL)
            return NULL;
         if(current_msg->msg_id == msg_id)
            return current_msg;
         else
            return NULL;
   }
}

/* Function to search a packet node in packet linked list.(Inner one)
 * Save location of current packet in each iteration of while() loop.
 * If full packet list is traversed in vain or packet node is found
 * with given packet node,  saved location of packet is returned.*/

struct pktnode *search_pkt(int pkt_id)
{
   current_pkt = head_pkt;
   save_pkt = current_pkt;
   while((current_pkt != NULL) && (pkt_id > current_pkt->pkt_id))
   {
      save_pkt = current_pkt;
      current_pkt = current_pkt->next;
   }
   return save_pkt;
}

/* Function to get packet info from packet string.
 * Tokenize the string by strtok() with delemeter ':'.
 */

void getPacketInfo(char *packet,  int *msg_id, int *pkt_id, char *message, int *prefix_len_msg)
{
   char *tokenPtr = NULL;
   char array[10][1500];
   char bkp_packet[2000];
   int counter = 0, i=0;
   
   /* Take a backup of the packet string as strtok() modifies the original string.*/
   strcpy(bkp_packet, packet);

   /* Extract first token. i.e. message id and save in temporary array.*/
   tokenPtr = (char *)strtok(packet, DELIM);
   if(tokenPtr == NULL)
   {
      printf("Fatal Error1 !! Invalid Message Format\n");
      cleanUpAll();
      exit(0);
   }
   strcpy(array[0], tokenPtr);
   counter++;

   /* Subsequent extraction of tokens and saving them.*/
   while(1)
   {
      tokenPtr = (char *)strtok(NULL, DELIM);
      if(tokenPtr == NULL)
         break;
      strcpy(array[counter], tokenPtr);
      /* Special measure to keep the delemeter when it is a part of packet message.
        * Concatinating : character to the previous token if current token counter
        * is > 2. */
      if(counter>2)
      strcat(array[counter-1], ":");
      counter++;
   }
   if(counter < 3)
   {
      printf("Fatal Error3 !! Invalid Message Format\n");
      cleanUpAll();
      exit(0);
   }
   *prefix_len_msg = getlen(array[0]);
   *msg_id = atoi(array[0]);
   *pkt_id = atoi(array[1]);
   for(i=2; i<counter; i++)
   {
      strcat(message, array[i]);
   }
}

int getlen(char *arg)
{
   int n=0;
   char ch;
   while(1)
   {
      ch = arg[n];
      if(ch != '0')
         break;
      n++;
   }
   return n;
}

/* Move through formulated linked list and display the content.*/
void display()
{
   char display_string[2000];
   char prefix[3];
   int i;

   current_msg = head_msg;
   while(current_msg != NULL)
   {
      for(i=0; i<current_msg->prefix_len; i++)
         prefix[i]= '0';
      prefix[i]='\0';
      sprintf(display_string, "Message %s%d\n", prefix, current_msg->msg_id);
      current_pkt = current_msg->pkthead;
      while(current_pkt != NULL)
      {
         strcat(display_string, current_pkt->message);
         current_pkt = current_pkt->next;
      }
      current_msg = current_msg->next;
      printf("%s\n", display_string);
   }
}

/* Move through linked list and deallocate it. Close file pointer also */

void cleanUpAll()
{
   fclose(fp);
   free(packet);
   while(head_msg != NULL)
   {
      head_pkt = head_msg->pkthead;
      while(head_pkt != NULL){
         free(head_pkt->message);
         current_pkt = head_pkt->next;
         free(head_pkt);
         head_pkt = current_pkt;
      }
      current_msg = head_msg->next;
      free(head_msg);
      head_msg = current_msg;
   }
}

/* Sort the message linked list,  i.e. the outer one.*/

void sortMsg()
{
   int tmp_id, tmp_len;
   struct pktnode *tmp_head;
   
   if(head_msg == NULL)
      return;
   else 
   {
      for(current_msg = head_msg;(current_msg != NULL);current_msg = current_msg->next)
      {
         for(save_msg = current_msg->next;(save_msg != NULL);save_msg = save_msg->next)
         {
            if(current_msg->msg_id > save_msg->msg_id)
            {
               tmp_id = save_msg->msg_id;
               tmp_head = save_msg->pkthead;
               tmp_len = save_msg->prefix_len;

               save_msg->msg_id = current_msg->msg_id;
               save_msg->pkthead = current_msg->pkthead;
               save_msg->prefix_len = current_msg->prefix_len;

               current_msg->msg_id = tmp_id;
               current_msg->pkthead = tmp_head;
               current_msg->prefix_len = tmp_len;
            }
         }
      }
   }
}

Tommo · 10-30-2007, 03:58 AM

Define the variables in main(), then pass them to the functions.

Taka · 10-30-2007, 04:04 AM

So...

Code:

int main(int argc,  char **argv)
{

   FILE *fp;
   char *packet;
   struct messagenode *head_msg, *save_msg, *current_msg;
   struct pktnode  *head_pkt, *save_pkt, *current_pkt;
   #define DELIM ":"

    if(argc != 2)
   {
      printf("Please provide one message data file\n");
      return -1;
   }

   initiate(argv[1]);

   while(1)
   {
       fgets(packet, 2001, fp);

      if(packet == NULL || !strcmp(packet, "END\n")|| !strcmp(packet, "END"))
         break;
      populateInList(packet);
   }
   sortMsg();

   display();
   
   cleanUpAll();
   return 0;
}

would be ok?

Taka · 10-30-2007, 04:06 AM

Or not because now the compiler hates me!

Elysia · 10-30-2007, 04:09 AM

Post the compile errors!

Tommo · 10-30-2007, 04:11 AM

Well, what do you think?

Lets look at a very simple example:

Code:

int a;
int b;
int add() {
  return a+b;
}
int main(void) {
  a = 1;
  b = 2;
  printf("a+b=%d\n",add());
  return 0;
}

Now, I have initialised two global variables here which both functions (main and add) can use. But what if I took them away and initialised them in main() ?

Code:

int add(int a, int b) {
  return a+b;
}
int main(void) {
  int a, b;
  a = 1;
  b = 2;
  printf("a+b=%d\n",add(a,b));
  return 0;
}

Here I initialise the variables in main() and pass them to the add function - add(int a, int b). I didn't need to do this before as they were declared globally. Do you understand?

Taka · 10-30-2007, 04:22 AM

Ok I get that, but won't I get argument errors when I compile?

matsp · 10-30-2007, 04:24 AM

Quote:

Originally Posted by Taka

Ok I get that, but won't I get argument errors when I compile?

Only if you do it wrong.

--
Mats

Elysia · 10-30-2007, 04:24 AM

Why would you?

matsp · 10-30-2007, 04:34 AM

Also, several of your global variables should really be local variables. Do you understand the difference between a global variable and a local variable? Do you understand how to use local variables?

I can also see some other problems in your code:

Code:

.... 
   packet = (char *)malloc(2000 * sizeof(char));
...
      fgets(packet, 2001, fp);
...

The purpose of using fgets() is to avoid buffer overflows - but it will rely on the fact that you use the same size buffer as the size given in fgets(). In your case, if the line is 2000 chracters long, the next byte after the buffer will be set to zero, resulting in "undefined behaviour".

--
Mats

Taka · 10-30-2007, 04:37 AM

Ok I've done something wrong. I tried to move just the

Code:

char *packet;

into the main and:

Code:

void initiate(char *filename, char *packet);
void cleanUpAll(char *packet);

void initiate(char *filename, char *packet)
{
   head_msg = NULL;
   head_pkt = NULL;

   fp = fopen(filename, "r");
   if(fp == NULL)
   {
      printf("Unable to open %s\n", filename);
      exit(0);
   }
   packet = (char *)malloc(2000 * sizeof(char));
}

void cleanUpAll(char *packet)
{
   fclose(fp);
   free(packet);
   while(head_msg != NULL)
   {
      head_pkt = head_msg->pkthead;
      while(head_pkt != NULL)
      {
         free(head_pkt->message);
         current_pkt = head_pkt->next;
         free(head_pkt);
         head_pkt = current_pkt;
      }
      current_msg = head_msg->next;
      free(head_msg);
      head_msg = current_msg;
   }
}

"assign2revise.c", line 50: prototype mismatch: 1 arg passed, 2 expected
"assign2revise.c", line 64: prototype mismatch: 0 args passed, 1 expected
"assign2revise.c", line 215: prototype mismatch: 0 args passed, 1 expected
"assign2revise.c", line 234: prototype mismatch: 0 args passed, 1 expected

Taka · 10-30-2007, 04:41 AM

Quote:

Originally Posted by matsp

Also, several of your global variables should really be local variables. Do you understand the difference between a global variable and a local variable? Do you understand how to use local variables?

I can also see some other problems in your code:

Code:

.... 
   packet = (char *)malloc(2000 * sizeof(char));
...
      fgets(packet, 2001, fp);
...

The purpose of using fgets() is to avoid buffer overflows - but it will rely on the fact that you use the same size buffer as the size given in fgets(). In your case, if the line is 2000 chracters long, the next byte after the buffer will be set to zero, resulting in "undefined behaviour".

--
Mats

So

Code:

  fgets(packet, 2001, fp);

should be

Code:

  fgets(packet, 2000, fp);

?

Elysia · 10-30-2007, 04:41 AM

Yes, that's correct.
Are you calling your functions correctly?

Code:

initiate(my_file_name, packet); // Works
initiate(my_file_name); // Does not work

matsp · 10-30-2007, 04:46 AM

Quote:

Originally Posted by Taka

"assign2revise.c", line 50: prototype mismatch: 1 arg passed, 2 expected
"assign2revise.c", line 64: prototype mismatch: 0 args passed, 1 expected
"assign2revise.c", line 215: prototype mismatch: 0 args passed, 1 expected
"assign2revise.c", line 234: prototype mismatch: 0 args passed, 1 expected

So, are you passing an extra parameter to initiate? [And the code won't work quite as you expect, since you need a pointer to pointer to modify your packet pointer value].

Not sure what those other lines are, don't make any sense in your posted code.

--
Mats

Taka · 10-30-2007, 04:47 AM

This is the fully revised code with the char global variable moved into main()

Code:

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

struct pktnode
{
   int pkt_id;
   char *message;
   struct pktnode *next;
};

struct messagenode
{
   int msg_id;
   int prefix_len;
   char id_prefix[3];
   struct pktnode *pkthead;
   struct messagenode *next;
};

FILE *fp;
struct messagenode *head_msg, *save_msg, *current_msg;
struct pktnode  *head_pkt, *save_pkt, *current_pkt;

#define DELIM ":"

void initiate(char *filename, char *packet);
void populateInList(char *packet);
struct messagenode *getMsgNode();
struct pktnode *getPktNode();
struct messagenode *search_msg(int msg_id);
struct pktnode *search_pkt(int pkt_id);
void getPacketInfo(char *packet,  int *msg_id, int *pkt_id, 
   char *message, int *prefix_len_msg);
void display();
void cleanUpAll(char *packet);
void sortMsg();
int getlen(char *arg);

int main(int argc,  char **argv)
{
   char *packet;

   if(argc != 2)
   {
      printf("Please provide one message data file\n");
      return -1;
   }
   initiate(argv[1]);

   while(1)
   {
      fgets(packet, 2000, fp);

      if(packet == NULL || !strcmp(packet, "END\n")|| !strcmp(packet, "END"))
         break;
      populateInList(packet);
   }
   sortMsg();

   display();
   
   cleanUpAll();
   return 0;
}

void initiate(char *filename, char *packet)
{
   head_msg = NULL;
   head_pkt = NULL;

   fp = fopen(filename, "r");
   if(fp == NULL)
   {
      printf("Unable to open %s\n", filename);
      exit(0);
   }
   packet = (char *)malloc(2000 * sizeof(char));
}

void populateInList(char *packet)
{
   int msg_id, pkt_id, prefix_len_msg;
   char *message;
   struct messagenode *tmp_message,  *loc;
   struct pktnode *tmp_packet,  *loc_pkt;

   message = (char *)malloc(1500*sizeof(char));
   
   getPacketInfo(packet, &msg_id, &pkt_id, message, &prefix_len_msg);
   
   if((loc = search_msg(msg_id)) != NULL)
   {
      tmp_packet = getPktNode();
      tmp_packet->pkt_id = pkt_id;
      tmp_packet->message = message;

      head_pkt = loc->pkthead;

      if(head_pkt == NULL)
         head_pkt = tmp_packet;
      else 
      {
         loc_pkt = search_pkt(pkt_id);

         if(loc_pkt == head_pkt && pkt_id < loc_pkt->pkt_id)
         {
            tmp_packet->next = head_pkt;
            head_pkt = tmp_packet;
            loc->pkthead = head_pkt;
         }  
         else 
         {
            tmp_packet->next = loc_pkt->next;
            loc_pkt->next = tmp_packet;
         }
      }
   }
   else
   {
      /* Second condition: loc==NULL i.e. Message entry not found */
      tmp_message = getMsgNode();
      tmp_message->msg_id = msg_id;
      tmp_message->prefix_len = prefix_len_msg;
      tmp_message->next = NULL;
      tmp_message->pkthead = getPktNode();
      tmp_message->pkthead->pkt_id = pkt_id;
      tmp_message->pkthead->message = message;
      
      if(head_msg == NULL)
         head_msg = tmp_message;
      else 
      {
         current_msg = head_msg;
         while(current_msg != NULL)
         {
            save_msg = current_msg;
            current_msg = current_msg->next;
         }
         save_msg->next = tmp_message;
      }
   }
}

struct messagenode * getMsgNode()
{
   struct messagenode *tmp;

   tmp = (struct messagenode *)malloc(sizeof(struct messagenode));
   tmp->pkthead = NULL;
   return tmp;
}

struct pktnode * getPktNode()
{
   struct pktnode *tmp;

   tmp = (struct pktnode *)malloc(sizeof(struct pktnode));
   tmp->next = NULL;
   return tmp;
}

/* Function to search a message node in message linked list */

struct messagenode *search_msg(int msg_id)
{
   current_msg = head_msg;
   if(head_msg == NULL)
      return NULL;
   else 
   {
      while((current_msg != NULL) && (current_msg->msg_id != msg_id))
         current_msg = current_msg->next;
      if(current_msg == NULL)
         return NULL;
      if(current_msg->msg_id == msg_id)
         return current_msg;
      else
         return NULL;
   }
}
 
/* Function to search a packet node in packet linked list */

struct pktnode *search_pkt(int pkt_id)
{
   current_pkt = head_pkt;
   save_pkt = current_pkt;

   while((current_pkt != NULL) && (pkt_id > current_pkt->pkt_id))
   {
      save_pkt = current_pkt;
      current_pkt = current_pkt->next;
   }
   return save_pkt;
}

/* Function to get packet info from packet string*/

void getPacketInfo(char *packet,  int *msg_id, int *pkt_id, 
   char *message, int *prefix_len_msg)
{
   char *tokenPtr = NULL;
   char array[10][1500];
   char bkp_packet[2000];
   int counter = 0, i=0;
   
   strcpy(bkp_packet, packet);

   tokenPtr = (char *)strtok(packet, DELIM);
   if(tokenPtr == NULL)
   {
      printf("Fatal Error1 !! Invalid Message Format\n");
      cleanUpAll();
      exit(0);
   }
   strcpy(array[0], tokenPtr);
   counter++;

   while(1)
   {
      tokenPtr = (char *)strtok(NULL, DELIM);
      if(tokenPtr == NULL)
         break;
      strcpy(array[counter], tokenPtr);
      if(counter>2)
         strcat(array[counter-1], ":");
      counter++;
   }
   if(counter < 3)
   {
      printf("Fatal Error3 !! Invalid Message Format\n");
      cleanUpAll();
      exit(0);
   }
   *prefix_len_msg = getlen(array[0]);
   *msg_id = atoi(array[0]);
   *pkt_id = atoi(array[1]);
   for(i=2; i<counter; i++)
   {
      strcat(message, array[i]);
   }
}

int getlen(char *arg)
{
   int n=0;
   char ch;

   while(1)
   {
      ch = arg[n];
      if(ch != '0')
         break;
      n++;
   }
   return n;
}

/* Move through formulated linked list and display the content.*/

void display()
{
   char display_string[2000];
   char prefix[3];
   int i;

   current_msg = head_msg;
   while(current_msg != NULL)
   {
      for(i=0; i<current_msg->prefix_len; i++)
         prefix[i]= '0';
      prefix[i]='\0';
      sprintf(display_string, "Message %s%d\n", prefix, 
         current_msg->msg_id);
      current_pkt = current_msg->pkthead;
      while(current_pkt != NULL)
      {
         strcat(display_string, current_pkt->message);
         current_pkt = current_pkt->next;
      }
      current_msg = current_msg->next;
      printf("%s\n", display_string);
   }
}

/* Move through linked list and deallocate it. Close file pointer also */

void cleanUpAll(char *packet)
{
   fclose(fp);
   free(packet);
   while(head_msg != NULL)
   {
      head_pkt = head_msg->pkthead;
      while(head_pkt != NULL)
      {
         free(head_pkt->message);
         current_pkt = head_pkt->next;
         free(head_pkt);
         head_pkt = current_pkt;
      }
      current_msg = head_msg->next;
      free(head_msg);
      head_msg = current_msg;
   }
}

/* Sort the message linked list*/

void sortMsg()
{
   int tmp_id, tmp_len;
   struct pktnode *tmp_head;
   
   if(head_msg == NULL)
      return;
   else 
   {
      for(current_msg = head_msg; (current_msg != NULL); 
         current_msg = current_msg->next)
      {
         for(save_msg = current_msg->next; 
            (save_msg != NULL); save_msg = save_msg->next)
         {
            if(current_msg->msg_id > save_msg->msg_id)
            {
               tmp_id = save_msg->msg_id;
               tmp_head = save_msg->pkthead;
               tmp_len = save_msg->prefix_len;

               save_msg->msg_id = current_msg->msg_id;
               save_msg->pkthead = current_msg->pkthead;
               save_msg->prefix_len = current_msg->prefix_len;

               current_msg->msg_id = tmp_id;
               current_msg->pkthead = tmp_head;
               current_msg->prefix_len = tmp_len;
            }
         }
      }
   }
}

10-30-2007, 03:58 AM	#2
Tommo Registered User Join Date: Jun 2007 Location: Scotland Posts: 101	Define the variables in main(), then pass them to the functions.
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10-30-2007, 04:06 AM	#4
Taka Registered User Join Date: Aug 2006 Posts: 127	Or not because now the compiler hates me!
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10-30-2007, 04:09 AM	#5
Elysia Mysterious C++ User Join Date: Oct 2007 Posts: 14,099	Post the compile errors!
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10-30-2007, 04:11 AM	#6
Tommo Registered User Join Date: Jun 2007 Location: Scotland Posts: 101	Well, what do you think? Lets look at a very simple example: Code: int a; int b; int add() { return a+b; } int main(void) { a = 1; b = 2; printf("a+b=%d\n",add()); return 0; } Now, I have initialised two global variables here which both functions (main and add) can use. But what if I took them away and initialised them in main() ? Code: int add(int a, int b) { return a+b; } int main(void) { int a, b; a = 1; b = 2; printf("a+b=%d\n",add(a,b)); return 0; } Here I initialise the variables in main() and pass them to the add function - add(int a, int b). I didn't need to do this before as they were declared globally. Do you understand?
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10-30-2007, 04:22 AM	#7
Taka Registered User Join Date: Aug 2006 Posts: 127	Ok I get that, but won't I get argument errors when I compile?
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10-30-2007, 04:24 AM	#9
Elysia Mysterious C++ User Join Date: Oct 2007 Posts: 14,099	Why would you?
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10-30-2007, 04:34 AM	#10
matsp Kernel hacker Join Date: Jul 2007 Location: Farncombe, Surrey, England Posts: 15,686	Also, several of your global variables should really be local variables. Do you understand the difference between a global variable and a local variable? Do you understand how to use local variables? I can also see some other problems in your code: Code: .... packet = (char )malloc(2000 sizeof(char)); ... fgets(packet, 2001, fp); ... The purpose of using fgets() is to avoid buffer overflows - but it will rely on the fact that you use the same size buffer as the size given in fgets(). In your case, if the line is 2000 chracters long, the next byte after the buffer will be set to zero, resulting in "undefined behaviour". -- Mats __________________ Compilers can produce warnings - make the compiler programmers happy: Use them! Please don't PM me for help - and no, I don't do help over instant messengers.
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10-30-2007, 04:41 AM	#13
Elysia Mysterious C++ User Join Date: Oct 2007 Posts: 14,099	Yes, that's correct. Are you calling your functions correctly? Code: initiate(my_file_name, packet); // Works initiate(my_file_name); // Does not work Last edited by Elysia; 10-30-2007 at 04:44 AM.
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