Reading File Issue

I'm pretty lost when it comes to reading/writing, I've paid attention in my class, read multiple online tutorials, and the book and I can't figure it out. I tried to do this assignment, but it just crashes when I execute it.

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#define MAXNUM 6


int main()
{
        FILE *fp;
        char *mode = "r";
        int i=0;
        char fName[MAXNUM] = {0}, lName[MAXNUM] = {0};
        int carNum[MAXNUM] = {0}, milesDriven[MAXNUM] = {0}, usedGallons[MAXNUM] = {0};
        double milesPerGallon[MAXNUM] = {0};
        int totalMiles = 0, totalGallons = 0;
        double totalMPG = 0, averageMPG = 0;

        fp = fopen("cars.dat", "r");

        if (fp == NULL)
        {
                printf("Can't open input file cars.dat!\n");
                exit(1);
        }

        for (i=0; i<MAXNUM; i++)
        {
                fscanf(fp, "&#37;c %c %d %d %d", fName[i], lName[i], carNum[i], milesDriven[i], usedGallons[i]);  //Assigns variables from file
                totalMiles += milesDriven[i];  //Sums total miles
                totalGallons += usedGallons[i];  //Sums total gallons
                milesPerGallon[i] = (milesDriven[i] / usedGallons[i]);  //Calculates MPG
        }

        for (i=0; i<MAXNUM; i++)
                totalMPG += milesPerGallon[i];  //Sums total MPG
        averageMPG = (totalMPG / MAXNUM);  //Calculates Avg MPG

       
        printf("Last_Name First_Name Car_No. Miles_Driven Gallons_Used MPG");  //print header
        for (i=0; i<MAXNUM; i++)  //prints charts
                printf("%c %c %d %d %d %d\n", fName[i], lName[i], carNum[i], milesDriven[i], usedGallons[i], milesPerGallon[i]);


        fclose(fp);
        getch();

        return 0;
}

---

After removing all the // comments, which are not legal C

Code:

---

$ gcc -W -Wall -ansi -pedantic -O2 foo.c
foo.c: In function `main':
foo.c:28: warning: format argument is not a pointer (arg 3)
foo.c:28: warning: format argument is not a pointer (arg 4)
foo.c:28: warning: format argument is not a pointer (arg 5)
foo.c:28: warning: format argument is not a pointer (arg 6)
foo.c:28: warning: format argument is not a pointer (arg 7)
foo.c:41: warning: int format, double arg (arg 7)
foo.c:10: warning: unused variable `mode'

---

Pay very close attention to the way you're calling printf and scanf functions.

I have no clue what any of that foo.c: things are, what did I do wrong when calling fscanf function?

Well, first, the warnings like these:

Code:

---

foo.c:28: warning: format argument is not a pointer (arg 3)

---

They mean that you're not passing fscanf() a pointer. That is, you have code like this

Code:

---

int i;
scanf("%d", i);

---

instead of like this

Code:

---

int i;
scanf("%d", &i);

---

This warning

Code:

---

foo.c:41: warning: int format, double arg (arg 7)

---

means that you have %d but need %f.

And this one

Code:

---

foo.c:10: warning: unused variable `mode'

---

means that you declare a variable called mode but you never use it. So you can get rid of the variable.

I think he means you are passing by value instead of by pointer

p.s. you should change:

Code:

---

fp = fopen("cars.dat", "r");

---

to:

Code:

---

fp = fopen("cars.dat", "r+b");

---

you shoudl also post the contents of cars.dat so we can check your input source

Quote:

---

Originally Posted by abachler

p.s. you should change:

Code:

---

fp = fopen("cars.dat", "r");

---

to:

Code:

---

fp = fopen("cars.dat", "r+b");

---

---

Why? The OP reads from the file with fscanf(), so it should be opened in text mode ('t'), not binary mode ('b'); and the program never attempts to write to the file, so there's no need to use "r+".

Alright, well I changed all my fscanf's with &'s, since I forgot them, but the program is still crashing.


*EDIT* All the program needs to do is read a .dat file, assign variables to the data, then display output stuff in a normal printf box, Im just confused on how exactly to assign file data to a variable, which is I believe why the program is crashing.

Code:

---

for (i=0; i<MAXNUM; i++)
        {
                fscanf(fp, "&#37;c", &fName[i]);          /**/
                fscanf(fp, "%c", &lName[i]);          /**/
                fscanf(fp, "%d", &carNum[i]);          /*Assigns variables from file*/
                fscanf(fp, "%d", &milesDriven[i]);    /**/
                fscanf(fp, "%d", &usedGallons[i]);    /**/
                totalMiles += milesDriven[i];  /*Sums total miles*/
                totalGallons += usedGallons[i];  /*Sums total gallons*/
                milesPerGallon[i] = (milesDriven[i] / usedGallons[i]);  /*Calculates MPG*/
        }

---

Code:

---

milesPerGallon[i] = (milesDriven[i] / usedGallons[i]);  /*Calculates MPG*/

---

Since both milesDriven[] and usedGallons[] are ints, you're performing integer division. The answer will be truncuated. I assume this is not what you want, because you're storing the result in a floating point variable, a double. Cast one of the numbers to a double:

Code:

---

milesPerGallon[i] = ((double)milesDriven[i] / usedGallons[i]);  /*Calculates MPG*/

---

How is it crashing?

You should enable warnings -- you get much better and more thorough diagnostics. For Dev-C++, in the Compiler Options dialog box, add "-W -Wall" (without quotes) to the "pass extra parameters to the compiler" option.

I am using Microsoft Visual C++ 6.0, so I'm not really sure where to turn on warning, id search for it, but something happened with the MSDN when I installed it and I do not have the CD (back at school).

I casted the one variable like you suggested and it didnt crash this time but I got a bunch of weird info, names were truncated and such it looks like

Code:

---

Last_Name  First_Name  Car_No.  Miles_Driven  Gallons_Used  MPG
J o 0 0 0 -1.#IND00
h n 0 0 0 -1.#IND00
J o 0 0 0 -1.#IND00
n e 0 0 0 -1.#IND00
s  55 250 20 12.500000

 M 0 0 0 -1.#IND00

---

The side spells "John Jones" which is suppose to be displayed on the same line, and "55", "250", "20", and "12.5" are right, but in the completely wrong place, suppose to all be on first line and look like "John Jones 55 250 20 12.5"

You want %c to read in "John"? Well, it's not going to. Try using a char[] array with %s.

Well I was trying to have this...

Code:

---

fscanf(fp, "%c", &fName[i]);

---

Assign fName[0] to be 'John'

Then this...

Code:

---

printf("%c", fName[0]);

---

Would print it, but it doesnt seem to be working.

*EDIT* I printed just the single fName[0] outside of a for statement and it just printed 1 char, so when its being assigned from the file its only assigning 1 char per array value.
fName[0] = J
fName[1] = o
fName[2] = h
fName[3] = n

Quote:

---

Originally Posted by dr0be

Well I was trying to have this...

Code:

---

fscanf(fp, "%c", &fName[i]);

---

Assign fName[0] to be 'John'

Then this...

Code:

---

printf("%c", fName[0]);

---

Would print it, but it doesnt seem to be working.

*EDIT* I printed just the single fName[0] outside of a for statement and it just printed 1 char, so when its being assigned from the file its only assigning 1 char per array value.
fName[0] = J
fName[1] = o
fName[2] = h
fName[3] = n

---

Right you are. %c tells fscanf to get just ONE char, not a whole string. Same with printf - %c tells it to output just one char, not a whole name.

Quote:

---

Originally Posted by Adak

Right you are. %c tells fscanf to get just ONE char, not a whole string. Same with printf - %c tells it to output just one char, not a whole name.

---

Alright, well I changed the scan and print to %s and the things just crashing again, this is so irritating.

Quote:

---

Originally Posted by dr0be

I am using Microsoft Visual C++ 6.0, so I'm not really sure where to turn on warning, id search for it, but something happened with the MSDN when I installed it and I do not have the CD (back at school).

---

Set the warning level by doing this (as with VC++ 2005 Express anyway):

1. Go to project > properties.
2. Expand the Configuration then C/C++ items then choose the "General" item.
3. You can see "warning level" on the right side.
4. Click on the area where the warning level is shown and a drop down menu appears. Choose "level 4" from the group.
5. Okay it and go to file > save all.
6. Rebuild (or just click the "test run" button) and you'll see any further warnings.

It may be a bit difference with VC6.

If the compiler switches/command lines aren't different, you could add a "/W?" without the quotes and replacing the ? with a number from 0 to 4. I'd suggest 4 for the highest warning level.

Alright, changed it to 4, and I still get no errors but program crashes when I execute. I got to be doing something wrong with the file or assigning the string values. Heres my current code at the moment.

Code:

---

int main()
{
        FILE *fp;
        char *mode = "r";
        int i=0;
        char *fName[MAXNUM], *lName[MAXNUM];
        int carNum[MAXNUM] = {0}, milesDriven[MAXNUM] = {0}, usedGallons[MAXNUM] = {0};
        double milesPerGallon[MAXNUM] = {0};
        int totalMiles = 0, totalGallons = 0;
        double totalMPG = 0, averageMPG = 0;

        fp = fopen("cars.dat", "r");

        if (fp == NULL)
        {
                printf("Can't open input file cars.dat!\n");
                exit(1);
        }

        for (i=0; i<MAXNUM; i++)
        {
                fscanf(fp, "&#37;s", &fName[i]);          /**/
                fscanf(fp, "%s", &lName[i]);          /**/
                fscanf(fp, "%d", &carNum[i]);        /*Assigns variables from file*/
                fscanf(fp, "%d", &milesDriven[i]);    /**/
                fscanf(fp, "%d", &usedGallons[i]);    /**/
                totalMiles += milesDriven[i];  /*Sums total miles*/
                totalGallons += usedGallons[i];  /*Sums total gallons*/
                milesPerGallon[i] = ((double)milesDriven[i] / usedGallons[i]);  /*Calculates MPG*/
        }

        for (i=0; i<MAXNUM; i++)
                totalMPG += milesPerGallon[i];  /*Sums total MPG*/
        averageMPG = (totalMPG / MAXNUM);  /*Calculates Avg MPG*/

       
        printf("Last_Name  First_Name  Car_No.  Miles_Driven  Gallons_Used  MPG\n");  /*print header*/
        for (i=0; i<MAXNUM; i++)
        {
                printf("%c", fName[i]);
                printf("%c", lName[i]);       
                printf("%d", carNum[i]);
                printf("%d", milesDriven[i]);
                printf("%d", usedGallons[i]);
                printf("%d", milesPerGallon[i]);
                printf("\n");
        }


        fclose(fp);
        getch();

        return 0;
}

---

The output it is giving me is weird, and the printf's seem right, so im assuming its how im assigning variables from the file. heres the output.

Code:

---

Last_Name  First_Name  Car_No.  Miles_Driven  Gallons_Used  MPG
JA9723815-1145324612
M 67350100
AS9910080
JJ8812386-1997659207
TM561000800
Ms0000

---

Do you, by chance, have array overflow? It's about all I can come up with. What this means is that, if you declare an array like this:

ExampleArray[10];

And you try to access ExampleArray[12], this will cause a crash. Check to make sure you don't have this, especially if you have some math in the brackets (like "ExampleArray[(Row*TotalColumns)+Column] = 0;".

The best way that I know of to finding where a crash occurs is to comment out all but one part of your code. If it works without crashing, remove some other area out of the commented out area and try again. If it crashes, you've found the culprit, but leave that area commented out and try the other areas as there could be more than one area. Once all bad areas are isolated, then find out what is going on. I did this quite regularly, and often filling functions with lots of debug-related things and using printf to display what the variable's values are to make sure they are working as expected.

Nah, its defiantly not that. Its assigning variables weird from the file. I know this because when I print the values they were assigned to Im getting weird values.

Heres my cars.dat file where its getting data from.

Code:

---

John Jones 55 250 20
Mary James 67 350 10
Amy Smith 99 100 8
Joe Johns 88 123 86
Trudy Mains 56 1000 80
Mary Ames 97 238 15

---

And heres how its assigning the variables...

Code:

---

for (i=0; i<MAXNUM; i++)
        {
                fscanf(fp, "%s", &fName[i]);          /**/
                fscanf(fp, "%s", &lName[i]);          /**/
                fscanf(fp, "%d", &carNum[i]);        /*Assigns variables from file*/
                fscanf(fp, "%d", &milesDriven[i]);    /**/
                fscanf(fp, "%d", &usedGallons[i]);    /**/
               
        }

---

So the actual file has spaces and numbers as characters in it? Using %d, %c, %s, and %f won't work in that case. I'm not sure how to do it in a reliable way (I can figure out how, but it's highly inefficient). You'd read the number and use either atoi or atof to convert a string into a number. Strings often require the null character in order to work. A space between numbers and words may not work but there's probably a method that allows for it to work. Someone else would have to assist you here.

I can make the data file look however I want, what are fields usually written with? quotes? what are they usually seperated by? commas?

Spaces, tabs, commas, and semicolons are common dividers, at least from what I've seen.

Quote:

---

Originally Posted by ulillillia

Spaces, tabs, commas, and semicolons are common dividers, at least from what I've seen.

---

Well any idea what im doing wrong when declaring variables from that file?

I wouldn't quite know other than than some sort of string parser. That is, it continues to read a string until set characters are encountered and when encountered, various functions are applied such as displaying the names first, then using atoi and atof to convert strings into numbers.

> char *fName[MAXNUM]
If you want an array of strings.

Code:

---

char fName[MAXNUM][MAXLEN];
...
fscanf(fp, "%s", fName[i]);
...
printf("%", fName[i]);

---

Quote:

---

Originally Posted by Salem

> char *fName[MAXNUM]
If you want an array of strings.

Code:

---

char fName[MAXNUM][MAXLEN];
...
fscanf(fp, "%s", fName[i]);
...
printf("%", fName[i]);

---

---

If I could hug you right now, I would. Thank you so much, was starting to feel hopeless.