help withcreating sequential text file

overlord21 · 09-24-2008, 02:27 PM

i have one last problem this day which is with the fread or printf :

Code:

 #include <stdio.h>
#include  <conio.h>
#include  <string.h>
typedef struct account

{
     char *name;
     char *password;
     char *previleges;   
        
        
        
        }account;
void account_write(char *);        
void fill_account(account);
void account_read(char *);





int main(){
    account c;
     char *filename="account.txt";
     account_write(filename);
     account_read(filename);
    
    getch();
    return 0;
    
    }
    
void fill_account(account *c)
{
     printf("give the name of account");
     scanf("%s",&c->name);
     printf("give the password");
     scanf("%s",&c->password);
     printf("give previliges");
     scanf("%s",&c->previleges);
     
     

     }

void account_write(char *filename)
{
     
    FILE  *file=fopen(filename,"ab");
    if(file!=NULL)
      { 
        account temp;
        fill_account(&temp);
        fwrite(&temp,sizeof (temp),1,file);
        
      
                  
                  
          } 
          
       fclose(file) ; 
 
     
     
     
     
     }

void account_read(char *filename)
   {

     FILE *file=fopen(filename,"rb");
     if(file!=NULL)
     { printf("f");
       account c;          
       fread(&c,sizeof (c),1,file);   
                  
                printf("%s, %s, %s",c.name,c.password,c.previleges );  
                   
     
     
     
     }
     fclose(file);
     }

this progra is supposed to read what we add as an account but still it crashes hope anyone can help with this

tabstop · 09-24-2008, 02:44 PM

There is no room to write to name, password, or privileges -- they are just pointers and you never give them anywhere to point to.

Note also that fwriting/freading pointers is a Bad Idea, since when your program stops and re-starts and tries to read in data, all that the file contains is the memory address where it used to live, and no actual data.

master5001 · 09-24-2008, 03:31 PM

I have a memory manager that I wrote one time that saves memory blocks in a file. If you do something similar to that, you could safely write out pointers. Long story short, tabstop is pointing out simply that what you are doing is probably different than what you are desiring to do.

overlord21 · 09-24-2008, 04:25 PM

should i give up using structures as pointers and chose them, as strings?

master5001 · 09-24-2008, 04:33 PM

In this case, maybe. If they are a fixed size you have to be writing them in a fixed size in order to properly fread() them.

Otherwise you will have to parse the file. I guess it really depends on how you intend to read stuff back into your program. Given your level of experience programming (and I am making assumptions at this point)

Example:

Code:

/* You don't want magic numbers */
#define FIELD_SIZE  32;

/* This is just me getting lazy since I don't want to rewrite too much of your code right now. */
typedef char field[FIELD_SIZE];

typedef struct account
{
  /* These are all arrays, don't worry */
  field name, password, previleges;   
}account;

Now you can read and write these just using fread() and fwrite() respectively. Obviously this isn't the best way to secure your data. But I doubt that is your objective for the time being.

overlord21 · 09-25-2008, 02:29 PM

please can anyone look at the problem of this program

Code:

#include <stdio.h>
#include  <conio.h>
#include  <string.h>
typedef struct account

{
     char name[20];
     char password[20];
     char previleges[20];   
        
        
        
        }account;
void account_write(char *);        
void fill_account(account);
void account_search(char *);
void print_account(account [],int);
void view_account(char *,int n);
void print_file(account [],int);
void account_delete(char *);

int main(){
    account c;
    int n;
    char *filename="account.txt";
    
   // account_write(filename);
    
     //account_search(filename);
    //view_account(filename,n);
     account_delete(filename);  
    getch();
    return 0;
    
    }
    
void fill_account(account *c)
{
     printf("give the name of account");
     scanf("%s",&c->name);
     printf("give the password");
     scanf("%s",&c->password);
     printf("give previliges");
     scanf("%s",&c->previleges);
     
     

     }

void account_write(char *filename)
{
     
    FILE  *file=fopen(filename,"ab");
    fflush(file);
    if(file!=NULL)
      { 
        account temp;
        fill_account(&temp);
        fwrite(&temp,sizeof (temp),1,file);
        
      
                  
                  
          } 
          
       fclose(file) ; 
 
     
     
     
     
     }
void account_search(char *filename)
   {int count=0,i=0; 
     char NAME[20];
     account t[20];
     FILE *file=fopen(filename,"rb");
     if(file!=NULL)
     {
                     
                                    
                          while(fread(&t[i],sizeof (account),1,file)==1)   
                            {   
                                i++;                           
                                count++; 
                            }                
     
                     
     
     }
     printf("give the name of account");
     scanf("%s",&NAME);
     for(int j=0;j<count;j++)
      {
         if(strcmp(t[j].name,NAME)==0)
           printf("%s \t %s\t %s \t",t[j].name,t[j].password,t[j].previleges);          
              
              }
          fclose(file);
    
     }

     
void account_delete(char *filename)
{
     
     
     
     int count=0,i=0; 
     char NAME[20];
     account t[20];
     FILE *file=fopen(filename,"wb");
     if(file!=NULL)
     {
                     
                                    
                          while(fread(&t[i],sizeof (account),1,file)==1)   
                            {   
                                i++;                           
                                count++; 
                            }                
     
                     
     
     }
     printf("give the name of account");
     scanf("%s",&NAME);
     for(int g=0;g<count;g++)
       {if(strcmp(t[g].name,NAME)==0)
           {  for(int h=g;h<count;h++)
                {
                     t[h]=t[h+1];
                    }
            }    
        }  
        count--;  
          print_file(t,count);
         
          fclose(file);                                          
     
     
     
     }
void print_file(account t[30],int n)
{
     for(int i=0;i<n;i++)
    { printf("%s",t[i].name); }    
     }

overlord21 · 09-25-2008, 02:31 PM

Code:

void account_delete(char *filename)
{
     
     
     
     int count=0,i=0; 
     char NAME[20];
     account t[20];
     FILE *file=fopen(filename,"wb");
     if(file!=NULL)
     {
                     
                                    
                          while(fread(&t[i],sizeof (account),1,file)==1)   
                            {   
                                i++;                           
                                count++; 
                            }                
     
                     
     
     }
     printf("give the name of account");
     scanf("%s",&NAME);
     for(int g=0;g<count;g++)
       {if(strcmp(t[g].name,NAME)==0)
           {  for(int h=g;h<count;h++)
                {
                     t[h]=t[h+1];
                    }
            }    
        }  
        count--;  
          print_file(t,count);
         
          fclose(file);

this ffunction has a role of deleting the found account but it has two problems: to delete from the string t[] and to overwrite/write in the file

overlord21 · 09-25-2008, 02:31 PM

please help

tabstop · 09-25-2008, 03:27 PM

And the symptoms of this problem are what, exactly?

overlord21 · 09-25-2008, 03:44 PM

the delete doesn't work i wrote the problems: can't write to file and can't delete from t[]

C_ntua · 09-25-2008, 04:10 PM

One bug is this:

Code:

scanf("%s",&NAME);

Common mistake for some reason. Remove the &. NAME is already a pointer. And rename NAME to name. Don't use capitals for variable names. Nothing wrong but it is bad style

I see you do this also in the rest of the code. Check your scanf(). The parameter has to have a type of char*. If you have an array like "char array[10]" then array is char*

overlord21 · 09-25-2008, 04:17 PM

Quote:

Originally Posted by overlord21

Code:

void account_delete(char *filename)
{
     
     
     
     int count=0,i=0; 
     char NAME[20];
     account t[20];
     FILE *file=fopen(filename,"wb");
     if(file!=NULL)
     {
                     
                                    
                          while(fread(&t[i],sizeof (account),1,file)==1)   
                            {   
                                i++;                           
                                count++; 
                            }                
     
                     
     
     }
     printf("give the name of account");
     scanf("%s",&NAME);
     for(int g=0;g<count;g++)
       {if(strcmp(t[g].name,NAME)==0)
           {  for(int h=g;h<count;h++)
                {
                     t[h]=t[h+1];
                    }
            }    
        }  
        count--;  
          print_file(t,count);
         
          fclose(file);

this ffunction has a role of deleting the found account but it has two problems: to delete from the string t[] and to overwrite/write in the file

the problem is that i want to delete an account using this code any help?

tabstop · 09-25-2008, 04:28 PM

Why do you think you can read from a file opened in mode "wb"?

overlord21 · 09-25-2008, 04:37 PM

i'm required to read and write in a binary file

tabstop · 09-25-2008, 04:43 PM

Quote:

Originally Posted by overlord21

i'm required to read and write in a binary file

Good for you. Have you bothered to look up fopen yet? Mode wb:

Quote:

truncate to zero length or create binary file for writing

If your file is now zero bytes long, how many records do you think you can read from it?

09-24-2008, 02:44 PM	#32
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,740	There is no room to write to name, password, or privileges -- they are just pointers and you never give them anywhere to point to. Note also that fwriting/freading pointers is a Bad Idea, since when your program stops and re-starts and tries to read in data, all that the file contains is the memory address where it used to live, and no actual data.
tabstop is offline

09-24-2008, 03:31 PM	#33
master5001 Banned Join Date: Aug 2001 Location: Visalia, CA, USA Posts: 3,699	I have a memory manager that I wrote one time that saves memory blocks in a file. If you do something similar to that, you could safely write out pointers. Long story short, tabstop is pointing out simply that what you are doing is probably different than what you are desiring to do.
master5001 is offline

09-24-2008, 04:25 PM	#34
overlord21 Registered User Join Date: May 2008 Posts: 70	should i give up using structures as pointers and chose them, as strings?
overlord21 is offline

09-24-2008, 04:33 PM	#35
master5001 Banned Join Date: Aug 2001 Location: Visalia, CA, USA Posts: 3,699	In this case, maybe. If they are a fixed size you have to be writing them in a fixed size in order to properly fread() them. Otherwise you will have to parse the file. I guess it really depends on how you intend to read stuff back into your program. Given your level of experience programming (and I am making assumptions at this point) Example: Code: /* You don't want magic numbers / #define FIELD_SIZE 32; / This is just me getting lazy since I don't want to rewrite too much of your code right now. / typedef char field[FIELD_SIZE]; typedef struct account { / These are all arrays, don't worry */ field name, password, previleges; }account; Now you can read and write these just using fread() and fwrite() respectively. Obviously this isn't the best way to secure your data. But I doubt that is your objective for the time being.
master5001 is offline

09-25-2008, 02:31 PM	#38
overlord21 Registered User Join Date: May 2008 Posts: 70	please help
overlord21 is offline

09-25-2008, 03:27 PM	#39
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,740	And the symptoms of this problem are what, exactly?
tabstop is offline

09-25-2008, 03:44 PM	#40
overlord21 Registered User Join Date: May 2008 Posts: 70	the delete doesn't work i wrote the problems: can't write to file and can't delete from t[]
overlord21 is offline

09-25-2008, 04:10 PM	#41
C_ntua Registered User Join Date: Jun 2008 Posts: 1,134	One bug is this: Code: scanf("%s",&NAME); Common mistake for some reason. Remove the &. NAME is already a pointer. And rename NAME to name. Don't use capitals for variable names. Nothing wrong but it is bad style I see you do this also in the rest of the code. Check your scanf(). The parameter has to have a type of char. If you have an array like "char array[10]" then array is char Last edited by C_ntua; 09-25-2008 at 04:17 PM.
C_ntua is offline

09-25-2008, 04:28 PM	#43
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,740	Why do you think you can read from a file opened in mode "wb"?
tabstop is offline

09-25-2008, 04:37 PM	#44
overlord21 Registered User Join Date: May 2008 Posts: 70	i'm required to read and write in a binary file
overlord21 is offline

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