Reading File Issue

[dr0be]

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.

#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;
}

[Salem]

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

$ 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.

[dr0be]

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

[dwks]

Well, first, the warnings like these:

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

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

instead of like this

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

This warning

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

means that you have %d but need %f.

And this one

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.

[abachler]

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

p.s. you should change:

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

to:

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

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

[dwks]

p.s. you should change:

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

to:

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+".

[dr0be]

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.

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*/
	}

[dwks]

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:

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.

[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).

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

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"

[dwks]

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

[dr0be]

Well I was trying to have this...

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

Assign fName[0] to be 'John'

Then this...

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

[Adak]

Well I was trying to have this...

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

Assign fName[0] to be 'John'

Then this...

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.

[dr0be]

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.

[ulillillia]

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.

[dr0be]

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.

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.

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