is random access possible on struct records in C language?
Sushma21 0 Newbie Poster
kvprajapati 1,826 Posting Genius Team Colleague
I guess, you are looking for Random Access IO. Take a look at http://c-faq.com/~scs/cclass/int/sx2i.html.
dkalita 110 Posting Pro in Training
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 0 Newbie Poster
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 110 Posting Pro in Training
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 0 Newbie Poster
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 110 Posting Pro in Training
this is the program where i input struct records...
#include<stdio.h>
#include<conio.h>
struct Product
{
end quote.
post your program properly.
Sushma21 0 Newbie Poster
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 0 Newbie Poster
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 110 Posting Pro in Training
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 0 Newbie Poster
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 110 Posting Pro in Training
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 1,826 Posting Genius Team Colleague
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 0 Newbie Poster
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 110 Posting Pro in Training
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 0 Newbie Poster
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 110 Posting Pro in Training
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 0 Newbie Poster
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 110 Posting Pro in Training
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 0 Newbie Poster
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 110 Posting Pro in Training
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 0 Newbie Poster
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 110 Posting Pro in Training
ya....i ll do that....i have turbo c++ compiler 3.0 version....is tat a problem??
that surely not an issue i guess
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