Thread: reading from bin file

Code:

original charge pc to reach within td
1
writting to file
do you want to 
1. enter a new set of values(max 5)
or
2.choose a saved set of values
2
which set of values do you want to use?
1
closing file
reopning file
answer 1
in while 1
1.000000

1.000000
userx@slackwhere:~/bin
$ 
userx@slackwhere:~/bin
$ ./read_write_binary_001
yep its here
Do you want to choose previously inputted values? (y/n)
y
which set of values do you want to use?
1
closing file
reopning file
answer 1
 
0.000000
userx@slackwhere:~/bin
$ cat file.bin
//empty file upon reopening on second run.

seeings how it is on a second run it maybe getting over written with nothing open close reopen might be clearing out your file.

well , even by switching fopen to a "wb+" and by removing the close(fp2) and adding a rewind just like before I keep getting a 0 output on the second run here's the code now:

Code:

int main()
{
    int i=0;
    int flag = FALSE;
    int flag2;
    int ans;
    INFO data2[5];
    FILE *fp2;
    double root , R;
    double check , check2;
    double f;
    char ans2;


     if (( fp2 = fopen(BINFILE, "wb+")) != NULL )
     {
         printf("Do you want to choose previously inputted values? (y/n)\n");
         fflush(stdin);
         scanf("%c",&ans2);


         if (ans2 == 'y')
            flag = TRUE;


            fp2 = fopen(BINFILE, "wb+");
    }


    while(i < 5 && flag==FALSE)
    {
      do
      {
          flag2 = TRUE;
        printf("Please enter the value for L:\n");
            scanf("%lf",&data2[i].l);
        printf("Please enter the value for C:\n");
            scanf("%lf",&data2[i].c);
        printf("Please enter the value for the battery voltage:\n");
            scanf("%lf",&data2[i].v);
        printf("Please enter the value for the dissipation time td:\n ");
            scanf("%lf",&data2[i].td);
        printf("Please enter the value for the percentage of the\n"
                "original charge pc to reach within td\n");
                scanf("%lf",&data2[i].pc);


        R = (-2* data2[i].l * log(data2[i].pc))/data2[i].td;
        check = 1/(data2[i].l*data2[i].c);
        check = check - pow((R/(2*data2[i].l)),2) ;
        check2 = sqrt(check);
        f = check2/(2*pi);
        f= 50/f;


        if(check < 0)
        {
           flag2 = FALSE;
           printf("Invalid input , Please enter a bigger value for td\n");
        }
        if(f < data2[i].td)
        {
            flag2 = FALSE;
            printf("Frequency too high; plot may be distorted\n");
        }




      }while(flag2 == FALSE);




        fwrite(&data2[i].l, sizeof(double), 1, fp2);
        fwrite(&data2[i].c, sizeof(double), 1, fp2);
        fwrite(&data2[i].v, sizeof(double), 1, fp2);
        fwrite(&data2[i].td, sizeof(double), 1, fp2);
        fwrite(&data2[i].pc, sizeof(double), 1, fp2);


        //fwrite(&data2, sizeof(data2), 1 ,fp2);
        i++;


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


        if (ans == 2)
            flag = TRUE;
    }


    printf("which set of values do you want to use?\n");
        scanf("%d",&ans);


    rewind(fp2);
    // compensate for zero element.
    if ( ans-1 > 6)
    {
        printf("out of bounds\n");
        return -1;
    }
    else
    {
        fread(&data2[ans-1].l, sizeof(double), 1, fp2);
        fread(&data2[ans-1].c, sizeof(double), 1, fp2);
        fread(&data2[ans-1].v, sizeof(double), 1, fp2);
        fread(&data2[ans-1].td, sizeof(double), 1, fp2);
        fread(&data2[ans-1].pc, sizeof(double), 1, fp2);
    }








printf("%lf\n",data2[ans-1].l);
findRoot(data2,ans,&root);


fclose(fp2);
return 0;


}

How can I prevent data loss after closing and reopening the file?

you might want to comment out a chunk of your code then work on getting information saving then reading your bin file printing it out again. then when you figure out how to fix that and get it fixed then move on to bigger things, and when wrong input is gotten how to re-ask for the proper input before moving on with getting more information.

that's what I am doing , is it possible that the program is not writing into the binary files ? thats why i get garbage values when i do the second run ? , I have been trying to figure this out all day , I tried all my ideas and all of the suggestions here and I am getting nowhere , Idk what to do anymore

change all of your fopens to

Code:

if ( (fp2 = fopen(BINFILE, "ab+"))

then run it and see if that helps ab+
becase I was not getting anything then I did that and got a return

Code:

userx@slackwhere:~/bin
$ ./read_write_binary_001
yep its here
Do you want to choose previously inputted values? (y/n)
y
in yes Tell = 40
which set of values do you want to use?
1
closing file
reopning file
answer 1
1.000000
1.000000
1.000000
1.000000
1.000000
in while 1
1.000000

yes it works now but what I would like to know why wouldn't it work with wb and rb ? because I didn't learn about ab+ in my programming class so I am not allowed to use it since it wasn't part of the course

i should have probably said something before, but don't do this:

Code:

     if (( fp2 = fopen(BINFILE, "wb")) != NULL )

     {
         printf("Do you want to choose previously inputted values? (y/n)\n");
         fflush(stdin);
         scanf("%c",&ans2);
 
 
         if (ans2 == 'y')
            flag = TRUE;
 
 

            fp2 = fopen(BINFILE, "wb");

    }

All that this does is open the file twice, and leak the first handle that you potentially got in the if(). Leaking file handles is potentially a problem, as the computer has a limited number available to begin with.

Better would be this:

Code:

fp2 = fopen(BINFILE, "wb");
if (fp2 != NULL) 
{
         printf("Do you want to choose previously inputted values? (y/n)\n");
         fflush(stdin);
         scanf("%c",&ans2);
 
         if (ans2 == 'y')
            flag = TRUE;
}

Also what if the file doesn't open? You should probably display an error and exit normally.

Originally Posted by Kamal Joub

yes it works now but what I would like to know why wouldn't it work with wb and rb ? because I didn't learn about ab+ in my programming class so I am not allowed to use it since it wasn't part of the course

"ab" mode may simply be what you wanted. "w" mode technically truncates a file (clears it) if it exists prior to opening for writing. This would erase information from previous runs of the program.

it's actually a university course towards my degree , a refund is kinda out of the question hahahahah, anyways I don't think it will a problem the professor is chill but I just wanted to know if alternatives were available just in case , anyways thanks for all the help guys

Originally Posted by Kamal Joub

it's actually a university course towards my degree , a refund is kinda out of the question hahahahah, anyways I don't think it will a problem the professor is chill but I just wanted to know if alternatives were available just in case , anyways thanks for all the help guys

did he actually say no you cannot excel in this class, you can only use covered material?

Originally Posted by Kamal Joub

it's actually a university course towards my degree , a refund is kinda out of the question hahahahah, anyways I don't think it will a problem the professor is chill but I just wanted to know if alternatives were available just in case , anyways thanks for all the help guys

Well, there are always alternatives, but they will be harder than simply using the right mode. One approach would be to open the file in "rb+" mode first. If it fails, then you know the file doesn't exist, and then you can safely try again with "wb" mode. If the file does open in "rb+" mode, you have a file, but will need to seek to the end before doing any writes.