Thread: print Random Files

hello ,
I have a simple problem a wanaa print form Random File
but the last printed twice???
this is the input
Enter the id :1

Enter the gpa :1.2

Enter the id :2

Enter the gpa :2.4

Enter the id :3

Enter the gpa :3.5

the size is : 3
the id is : 1 the gpa is: 1.20
the id is : 2 the gpa is: 2.40
the id is : 2 the gpa is: 2.40 /// why twice?
Press any key to continue
the code

Code:

#include<stdio.h>
/*********** Data ***********/
typedef struct {
	int id;
	float gpa;
}data;
/*********** The functions ***********/
void read(data*);
void print(FILE*);
/*********** Main ***********/
int main(){
	data R;
	FILE *f;
	int i;
	if((f=fopen("f.dat","w"))==NULL)
		printf("sorry i can not open the file\n");
	else{
		fseek(f,sizeof(data),SEEK_SET);
	for(i=1;i<=3;i++){
		read(&R);
		fseek(f,sizeof(data)*(i-1),SEEK_SET);
		fwrite(&R,sizeof(data),1,f);
	}
	}
	print(f);
	return 0;
}

/*********** Read ***********/
void read(data *R){
	printf("Enter the id :");
	scanf("%d",&R->id);
	printf("\n");
	printf("Enter the gpa :");
	scanf("%f",&R->gpa);
	printf("\n");
}

/*********** Print ***********/
void print(FILE *f){
	data R;
	int n=0,i;
		if((f=fopen("f.dat","r"))==NULL)
		printf("sorry i can not open the file\n");
	else{
	fseek(f,sizeof(data),SEEK_END);
	n=ftell(f)/sizeof(data);
	printf("the size is : %d\n",n);
	for(i=1;i<=n;i++){
		fseek(f,sizeof(data)*(i-1),SEEK_SET);
		fread(&R,sizeof(data),1,f);
		printf("the id is : %d the gpa is: %.2f \n",R.id,R.gpa);
	}
	fclose(f);
	}
}
/*********** End ***********/

1. You missed to close the file before opening the file for reading and after writing ...it is veru important of there are chances of you lossing last written data. This is very imp. in file handling.

2. The same data was not getting printed twice as u mentioned..try intializing the variable "R" after each read then u will come to know the reason.

3. After fseek if u do ftell the result will always be original size of file + the size you tried to fseek. Hence you need not do

i<=n in for loop.

The working code is as follows



N'joy....

Code:

int main(){
        data R;
        FILE *f;
        int i;
        if((f=fopen("f.dat","w"))==NULL)
                printf("sorry i can not open the file\n");
        else{
                fseek(f,sizeof(data),SEEK_SET);
        for(i=1;i<=3;i++){
                read(&R);
                fseek(f,sizeof(data)*(i-1),SEEK_SET);
                fwrite(&R,sizeof(data),1,f);
        }
        }
        fclose(f);
        print(f);
        return 0;
}

/*********** Read ***********/
void read(data *R){
        printf("Enter the id :");
        scanf("%d",&R->id);
        printf("\n");
        printf("Enter the gpa :");
        scanf("%f",&R->gpa);
        printf("\n");
}

/*********** Print ***********/
void print(FILE *f){
        data R;
        int n=0,i;
                if((f=fopen("f.dat","r"))==NULL)
                printf("sorry i can not open the file\n");
        else{
        fseek(f,sizeof(data),SEEK_END);
        n=ftell(f)/sizeof(data);
        printf("the size is : %d\n",n);
        for(i=1;i<n;i++){
                fseek(f,sizeof(data)*(i-1),SEEK_SET);
                fread(&R,sizeof(data),1,f);
                printf("the id is : %d the gpa is: %.2f \n",R.id,R.gpa);
                R.id = 0;
                R.gpa = 0;
        }
        fclose(f);
        }
}
/*********** End ***********/

thank u cisgreat
thank u WaltP
i know my problem now
thank u again

yup ur right waltp...actually ...i due to reformatting i missed the if else..part....anyways..thanks for that...!!