binary file input and out

**Kamal Joub** · 11-20-2017

ok so i am trying to make a program in which the user can input 5 values then , these values are to be stored in a binary file.

Then I have to read the stored value from the binary file.

However , i keep getting a random number totally unrelated to the inputs.

here's my code please disregard the printf function it's just for testing the output.Also , note that i am only using data[].l and not the whole structure as a test .

Code:

#include <stdio.h>
#include <math.h>


#define N 100  // number of points
#define TRUE 1
#define FALSE 0
#define EPSILON 1e-10
#define BINFILE "file.bin"


typedef struct
{


   double l; // starting time
   double c; // ending time
   double v; // velocity
   double td; // time
   double pc; // altitude


} INFO;


int main()
{
  INFO data[5];
  int i=0;
  int flag = FALSE;
  int ans;
  FILE *fp;


  while(i < 5 && flag==FALSE)
{
    printf("Please enter the value for L:\n");
    scanf("%lf",&data[i].l);
    printf("Please enter the value for C:\n");
    scanf("%lf",&data[i].c);
    printf("Please enter the value for the battery voltage:\n");
    scanf("%lf",&data[i].v);
    printf("Please enter the value for the dissipation time td:\n ");
    scanf("%lf",&data[i].td);
    printf("Please enter the value for the percentage of the ");
    printf("\n original charge pc to reach within td\n");
    scanf("%lf",&data[i].pc);
    i = i+1;


    printf("do you want to 1. enter a new set of values(max 5) and save these values\n");
    printf("or 2.choose a saved set of values\n");
    scanf("%d",&ans);


    if(ans==1)
     {
        fp = fopen(BINFILE, "wb");
        fwrite(&data[i].l, sizeof(double), 1, fp);
        fclose(fp);
     }
    else
     {  flag = TRUE;
        fp=fopen(BINFILE, "rb");
        fread(&data[5].l,sizeof(double),1,fp);
        fclose(fp);
     }
}




printf("%lf",data[5].l);








}

**jimblumberg** · 11-20-2017

Look at this snippet:

Code:

 
    if(ans==1)
     {
        fp = fopen(BINFILE, "wb");
        fwrite(&data[i].l, sizeof(double), 1, fp);
        fclose(fp);
     }
    else
     {  flag = TRUE;
        fp=fopen(BINFILE, "rb");
        fread(&data[5].l,sizeof(double),1,fp);
        fclose(fp);
     }
}
 
 
 
 
printf("%lf",data[5].l);

What is the size of your array?

With that sized array what are the valid indexes available?

You're accessing your array out of bounds, so I would expect garbage output.

**~~userxbw~~** · 11-20-2017

....

**Kamal Joub** · 11-20-2017

jimblumberg but my array is data[5] , hence it's of size 5 , how am i accessing it out of bounds ?

and

userxbw , i dont understand what you mean , could you elaborate please ?

**jimblumberg** · 11-20-2017

but my array is data[5] , hence it's of size 5 , how am i accessing it out of bounds ?

Look at this snippet:

Code:

  
printf("%lf",data[5].l);

Do you know that arrays in C start at zero and stop at size - 1? This means that the valid elements of your array would be 0, 1, 2, 3, and 4. Element 5 is outside the bounds of your array.

**~~userxbw~~** · 11-20-2017

while loop goes

Code:

while ( i < 5)
{
   something[i] = "do da"; // but i = what when you're trying to access it on which loop interval ?

  print(something[5]);
i++;
}

if that loop not go 5 times what do you think you're going to get if you try to get to 5 when only on 3?
plus more thinking array[5] = 0 - 4 to last element as well. as stated

**~~userxbw~~** · 11-20-2017

nevermind;;

**Kamal Joub** · 11-20-2017

well i increased the size of the array and it didn't change anything at all

**whiteflags** · 11-20-2017

I think it would be easier to fread() or fwrite() the whole structure.

**jimblumberg** · 11-20-2017

Why did you increase the size of the array? You really need learn to stay within the bounds of your array.

If you're still having problems post the smallest possible code that illustrates the problem. Which means remove everything that is not necessary to seeing the problem.

**Kamal Joub** · 11-20-2017

whiteflag , i'd like to do that but can it be done in a single fread and fwrite ?

jim , idk what the hell you're talking about first you say element 5 is outside the bounds of my array , so i increase the size of the array so it would be within the bounds.like for real man you're contradicting yourself

**~~userxbw~~** · 11-20-2017

Originally Posted by Kamal Joub

whiteflag , i'd like to do that but can it be done in a single fread and fwrite ?

if you can figure out how to put one in then just repeat the process for the others ones.

Originally Posted by Kamal Joub

jim , idk what the hell you're talking about first you say element 5 is outside the bounds of my array , so i increase the size of the array so it would be within the bounds.like for real man you're contradicting yourself

he means to just back off by one number to eliminate over running your array. They are zero based, or you can keep doing it that way, and do not access the zero element.

**~~userxbw~~** · 11-20-2017

running your program your logic seems to be off to begin with.

Code:

D:\>
D:\>TextFile1
Please enter the value for L:
23
Please enter the value for C:
44
Please enter the value for the battery voltage:
55
Please enter the value for the dissipation time td:
 66
Please enter the value for the percentage of the
 original charge pc to reach within td
77
do you want to 1. enter a new set of values(max 5) and save these values
or 2.choose a saved set of values
1
Please enter the value for L:
22
Please enter the value for C:
33
Please enter the value for the battery voltage:
44
Please enter the value for the dissipation time td:
 55
Please enter the value for the percentage of the
 original charge pc to reach within td
66
do you want to 1. enter a new set of values(max 5) and save these values
or 2.choose a saved set of values
2
0.000000

if you select 1 it is suppose to save whatever, then ask for more. if 2 it is just suppose to save. when you have it reading from the file. and even on first run if 2 is selected how to get input that has not been saved?

in file bin

Code:

`K¤K

let me tinker with this some more.

**Kamal Joub** · 11-20-2017

if the user just started the program he is supposed to choose 1 before 2 because there will be no data to choose from , and i'm using the extra element in data[] to store the data read from file bin but as you indicated file it is not writing the correct value in file bin to begin with , i am still working on it but I don't seem to figure it out

**whiteflags** · 11-20-2017

whiteflag , i'd like to do that but can it be done in a single fread and fwrite ?

Yes it can. This is what you have now.

Code:

    if(ans==1)
     {
        fp = fopen(BINFILE, "wb");
        fwrite(&data[i].l, sizeof(double), 1, fp);
        fclose(fp);
     }
    else
     {  flag = TRUE;
        fp=fopen(BINFILE, "rb");
        fread(&data[5].l,sizeof(double),1,fp);
        fclose(fp);
     }

This just reads and writes l. Writing the whole structure is a minor change to the relevant function arguments.

Code:

fwrite(&data[i], sizeof data[i], 1, fp);

fread(&data[i], sizeof data[i], 1, fp);

One structure has all five values in it, so I am starting to think that you won't need the array anymore either.

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