Random Access

[Sushma21]

is random access possible on struct records in C language?

[kvprajapati]

I guess, you are looking for Random Access IO. Take a look at http://c-faq.com/~scs/cclass/int/sx2i.html.

[dkalita]

what do u mean by that ?
If u want to randomly access some struct records u can make an array of that struct and proceed........

[Sushma21]

what do u mean by that ?
If u want to randomly access some struct records u can make an array of that struct and proceed........

ya...i tried doing that....i accepted array of records in 1 program and tried to access it randomly in other program by opening the file in read mode and using fseek and fread functions....but it is showing some garbage values....so i have a doubt if we can acess struct records randomly like tat??
thanks in advance...

[dkalita]

ya...i tried doing that....i accepted array of records in 1 program and tried to access it randomly in other program by opening the file in read mode and using fseek and fread functions....but it is showing some garbage values....so i have a doubt if we can acess struct records randomly like tat??
thanks in advance...

u are going in the exact direction.
U are getting garbage value is may be because u are not reading in the way u wrote to that file.
U have to use fwrite() for writting then only u will get correct values using fread().

typedef struct
{
 /*your data*/
} myStruct;

int index = 3; // e.g.
myStruct *buf;
int sizeOfStruct = sizeof(myStruct);
fseek(fp, sizeOfStruct*index, SEEK_SET);
if(feof(fp))
{
    cout<<"index out of bound";
    exit(1);
}
else
{
     if(fread(buf, sizeOfStruct, 1, fp)==sizeOfStruct)
     {
            /*your struct is in "buf" 
             *access its member using -> operator*/
     }
      else
      {
             /*data not present*/
             exit(1);
       }
}

and for writting u have to write as

myStruct m;
fwrite(&m, sizeOfStruct, 1, fp);

[Sushma21]

u are going in the exact direction.
U are getting garbage value is may be because u are not reading in the way u wrote to that file.
U have to use fwrite() for writting then only u will get correct values using fread().

typedef struct
{
 /*your data*/
} myStruct;

int index = 3; // e.g.
myStruct *buf;
int sizeOfStruct = sizeof(myStruct);
fseek(fp, sizeOfStruct*index, SEEK_SET);
if(feof(fp))
{
    cout<<"index out of bound";
    exit(1);
}
else
{
     if(fread(buf, sizeOfStruct, 1, fp)==sizeOfStruct)
     {
            /*your struct is in "buf" 
             *access its member using -> operator*/
     }
      else
      {
             /*data not present*/
             exit(1);
       }
}

and for writting u have to write as

myStruct m;
fwrite(&m, sizeOfStruct, 1, fp);

end quote.

this is the program where i input struct records...

#include<stdio.h>
#include<conio.h>
struct Product
{

[dkalita]

this is the program where i input struct records...

#include<stdio.h>
#include<conio.h>
struct Product
{

end quote.

post your program properly.

[Sushma21]

post your program properly.

this is the program where i input struct records...

#include<stdio.h>
#include<conio.h>
struct product
{
     char name[20];
      int no;
      float  price;
};
product read_rec()
{
        product p;
         printf("enter the name, number and price\n");
         scanf("%s%d%f",&p.name,&p.number,&p.price);
         return p;
}
void main()
{
       FILE *fp;
        product p[20];
       int size,i,k;
      clrscr();
       fopen=("records","w");
        if(fp==NULL)
       {
              printf("error in opening file\n");
               exit(0);
        }
        printf("enter the number of records\n");
        scanf("%d",&size);
        printf("enter the records\n");
        for(i=0;i<size;i++)
        {
                  p[i]=read_rec();
         }
          fwrite(p,(size*sizeof(p)),size,fp);
          fclose(fp);
          getch();
}

[Sushma21]

this the program where i m trying to access the records randomly....

#include<stdio.h>
#include<conio.h>
struct record
{
 char name[20];
int no;
float price;
};
void main()
{
FILE *fp;
int i;
product p[20],j;
clrscr();
fp=fopen("records","r");
printf("enter the element to accessed\n");
scanf("%d",&i);
fseek(fp,(i*sizeof(p[i])),SEEK_SET);
fread(&j,sizeof(p[i]),1,fp);
printf("name=%s\nno=%d\nprice=%f",j.name,j.no,j.price);
fclose(fp);
getch();
}

[dkalita]

1> u are doing

fwrite(p,(size*sizeof(p)),size,fp);

which tries to write the whole things together. Better try the following in the file for writting

for(i=0;i<size;i++)
        {
                p[i]=read_rec();
                fwrite(&p[i], sizeof(product), 1, fp);
        }

and hence u wont need the p[] array u can do

product p;
//other code
for(i=0;i<size;i++)
        {
                p=read_rec();
                fwrite(&p, sizeof(product), 1, fp);
        }

test it and inform me..........

2> use CODE tag to embed codes

3> try to define struct like

typedef struct
{
      //members
} product;

That is a good practice.

4> u are writting

fseek(fp,(i*sizeof(p[i])),SEEK_SET);

u should write

fseek(fp, i*sizeof(product), SEEK_SET);

these are good programming practice

[Sushma21]

1> u are doing

fwrite(p,(size*sizeof(p)),size,fp);

which tries to write the whole things together. Better try the following in the file for writting

for(i=0;i<size;i++)
        {
                p[i]=read_rec();
                fwrite(&p[i], sizeof(product), 1, fp);
        }

and hence u wont need the p[] array u can do

product p;
//other code
for(i=0;i<size;i++)
        {
                p=read_rec();
                fwrite(&p, sizeof(product), 1, fp);
        }

test it and inform me..........

2> use CODE tag to embed codes

3> try to define struct like

typedef struct
{
      //members
} product;

That is a good practice.

4> u are writting

fseek(fp,(i*sizeof(p[i])),SEEK_SET);

u should write

fseek(fp, i*sizeof(product), SEEK_SET);

these are good programming practice

i tried doing it....but still its showing garbage values.,....what else can be done??

[dkalita]

i tried doing it....but still its showing garbage values.,....what else can be done??

check the attachments.........
It does what u r trying to do. I have tested them

[kvprajapati]

Open/Create a data file using binary mode. c file io

FILE *fp;
fp=fopen("c:\\test.bin", "wb");
char x[10]="ABCDEFGHIJ";
fwrite(x, sizeof(x[0]), sizeof(x)/sizeof(x[0]), fp);

Use,

int main(){
    ...
    return 0;
}

Should I use void main() or int main()?

SUMMARY:
...
main() must return int. Not void, not bool, not float. int. Just int, nothing but int, only int.
...

[Sushma21]

check the attachments.........
It does what u r trying to do. I have tested them

did read.c work??it isn't working here.....its not abt syntax errors.....but.....the records aren't getting saved in the disc....if i try to read the records from the dos shell its showing some junk values.....what could be the problem???

[dkalita]

did read.c work??it isn't working here.....its not abt syntax errors.....but.....the records aren't getting saved in the disc....if i try to read the records from the dos shell its showing some junk values.....what could be the problem???

I have tested the read.c file in my machine which was working properly.

You can't read the doc like that since I used fwrite() which writes the stuff in binary format. U can read them using the read.c file only. Run it and see.
If u want them to be readable like that then u have to use fprintf() for writting and fscanf() for reading and in that case u wont be able to do a random access because u dont know how many bytes is taken by each data.

Read more on file operations in C/C++. U need to know more about them.

[Sushma21]

I have tested the read.c file in my machine which was working properly.

You can't read the doc like that since I used fwrite() which writes the stuff in binary format. U can read them using the read.c file only. Run it and see.
If u want them to be readable like that then u have to use fprintf() for writting and fscanf() for reading and in that case u wont be able to do a random access because u dont know how many bytes is taken by each data.

Read more on file operations in C/C++. U need to know more about them.

i m sorry if i m being stupid......i just have a doubt.....how should i run a program from dos shell??

[dkalita]

i m sorry if i m being stupid......i just have a doubt.....how should i run a program from dos shell??

Do u have turboC/borlandC in your machine.
If so open your file in it. In the main menu there are options for compiling and running your program.

Otherwise u have to get a copy of either turboC or borland C and put it in your machine.

After compilation u can directly run from there using the menu. Or u can exit turboC and in the command promt type the exe created by the compiler and press enter.

[Sushma21]

Do u have turboC/borlandC in your machine.
If so open your file in it. In the main menu there are options for compiling and running your program.

Otherwise u have to get a copy of either turboC or borland C and put it in your machine.

After compilation u can directly run from there using the menu. Or u can exit turboC and in the command promt type the exe created by the compiler and press enter.

i have turboc++ compiler.......running and executing is not a problem.......but i am not able to access it randomly in the second program.............

[dkalita]

i have turboc++ compiler.......running and executing is not a problem.......but i am not able to access it randomly in the second program.............

can u send me a snapsot of the input/output for the read.c program.
Also send me a snapshot of the inputs given to the write.c program.

[Sushma21]

can u send me a snapsot of the input/output for the read.c program.
Also send me a snapshot of the inputs given to the write.c program.

output of read.c program is something like this:
enter the number of records
3
enter the name,no and price
pen
10
10
enter the name, no and price
pencil
10
10
enter the name, no and price
eraser
30
30
just a sample one........
the program is terminated there.....
output of a second program goes like this....
enter the number of record to be accessed
1
name=
number=37088
price=4372412820000000000.000000

[dkalita]

i am not sure exactly where is the problem because when I run that program i got correct results.
Do one thing, post the two programs that u are using. I will have look at it

[Sushma21]

i am not sure exactly where is the problem because when I run that program i got correct results.
Do one thing, post the two programs that u are using. I will have look at it

ya....i ll do that....i have turbo c++ compiler 3.0 version....is tat a problem??

[dkalita]

ya....i ll do that....i have turbo c++ compiler 3.0 version....is tat a problem??

that surely not an issue i guess