Methods and file pointers

I am pretty confident that I wrote my requestFileName correctly, but my program crashes every time I run it, so I am assuming I wrote out fileScan incorrectly.

Code:

---


void requestFileName(FILE **fp)
{ 
        char inputFilename[30];                                // Character Array to hold the users specified input file name
        printf("Enter the name of the file to be scanned: ");       
        scanf("%s", inputFilename);                        // Scans the input file specified by the user       
        printf("\n");                                                // adds a space in between file names and file statistics       
        *fp = fopen(inputFilename, "r");        // open the file as read-only
}
/*        Stores values from the input file into the variables cityName, population, squareMileafe, pollution,
        crime, expense, and highways. */
void fileScan(FILE **fp, char cityName, int population, int squareMileage, int pollution, int crime, int expense, int highways)
{
        fscanf(fp, "%s %d %d %d %d %d %d", cityName, population, squareMileage, pollution, crime, expense, highways);
}

---

In my main method I call fileScan like:

Code:

---

while(fileScan(&fp, cityName, population, squareMileage, pollution, crime, expense, highways) != EOF)        // get next char from input file until we reach EOF
        {
//...
        }

---

What am i doing incorrectly?

Code:

---

void requestFileName(FILE *fp)  /* remove one  * */
{ 
        char inputFilename[30];                                // Character Array to hold the users specified input file name
        printf("Enter the name of the file to be scanned: ");       
        scanf("%s", inputFilename);
        printf("\n");                                                // adds a space in between file names and file statistics       
        fp = fopen(inputFilename, "r");        /* remove the * in *fp */
}

/*
 * remove the extra * in fp and add to char *cityName
 */
void fileScan(FILE *fp, char *cityName, int population, int squareMileage, int pollution, int crime, int expense, int highways)
{
        fscanf(fp, "%s %d %d %d %d %d %d", cityName, population, squareMileage, pollution, crime, expense, highways);
}

---

In my main method I call fileScan like:

Code:

---

/*
 * remove the extra & at fp
 *
 * fileScan does return any value therefore while can't work checking if it is the EOF
 * population, squareMilege, pollution, crime, expense, highways are not the same that in the function;
 * those are a copy
 */
while(fileScan(fp, cityName, population, squareMileage, pollution, crime, expense, highways) != EOF)        // get next char from input file until we reach EOF
        {
//...
        }

---

Quote:

---

Originally Posted by Aia

Code:

---

void requestFileName(FILE *fp)  /* remove one  * */
{ 
        char inputFilename[30];                                // Character Array to hold the users specified input file name
        printf("Enter the name of the file to be scanned: ");       
        scanf("%s", inputFilename);
        printf("\n");                                                // adds a space in between file names and file statistics       
        fp = fopen(inputFilename, "r");        /* remove the * in *fp */
}

---

---

My professor told me i needed to use FILE **fp. :\ but maybe I misunderstood.

If you're supposed to use FILE **fp, then make sure your fscanf has *fp as the first argument.

Edit: although I can't think of a good reason (or, for that matter, any reason at all, really) for you to need **fp here. (The whole point of everything in C using FILE * was that you could pass it around functions and everything would work the way you expect.)

I also get this as a warning:

"Warning 3 warning C4013: 'fileScan' undefined; assuming extern returning int"

Is it not working correctly because fileScan is not returning the correct declaration?

Code:

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fscanf(fp, "%d", &population);

---

for most formats (except %s) you need to add & before var - because scanf need a pointer to var where it will store the parsed value

Quote:

---

Originally Posted by drater

I also get this as a warning:

"Warning 3 warning C4013: 'fileScan' undefined; assuming extern returning int"

Is it not working correctly because fileScan is not returning the correct declaration?

---

It means just what it says: you haven't defined a function called fileScan.

Now you may have done so later in the file, but by then the damage is done. You did remember to put a function prototype of fileScan at the top of the file, didn't you?

'fileScan' is not returning any return code - it is defined as void
if you want to return EOF on error - change you 'fileScan' function to return it if fcanf failed

I took out the void, and Now i am getting 2 warnings which I don't understand:
Warning 3 warning C4028: formal parameter 1 different from declaration
Warning 4 warning C4028: formal parameter 2 different from declaration

Code:

---


/*        Requests the user to input a valid file name to be scanned */
void requestFileName(FILE **fp)
{ 
        char inputFilename[30];                                // Character Array to hold the users specified input file name
        printf("Enter the name of the file to be scanned: ");       
        scanf("%s", inputFilename);                        // Scans the input file specified by the user       
        printf("\n");                                                // adds a space in between file names and file statistics       
        *fp = fopen(inputFilename, "r");        // open the file as read-only
}

/*        Stores values from the input file into the variables cityName, population, squareMileafe, pollution,
        crime, expense, and highways. */
fileScan(FILE *fp, char cityName, int population, int squareMileage, int pollution, int crime, int expense, int highways)
{ /*    BOTH ERRORS APPEAR HERE    */

        fscanf(fp, "%s %d %d %d %d %d %d", cityName, population, squareMileage, pollution, crime, expense, highways);
}

---

Reading strings with scanf calls for extra caution. I suggest you read this:
http://cboard.cprogramming.com/showp...37&postcount=9

Quote:

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Originally Posted by drater

I took out the void, and Now i am getting 2 warnings which I don't understand:
Warning 3 warning C4028: formal parameter 1 different from declaration
Warning 4 warning C4028: formal parameter 2 different from declaration

---

It means your definition and declaration doesn't match.
And remember that all functions should return something. Not nothing. If it doesn't need to return anything, it should return void. In your case, it should return int.
And as mentioned, update your prototype to match the new definition.

do not just remove void - replace it by the proper type for example int

show the following:
function prototype
function definition
function call
mark line where the error occured

Quote:

---

Originally Posted by drater

I took out the void, and Now i am getting 2 warnings which I don't understand:
Warning 3 warning C4028: formal parameter 1 different from declaration
Warning 4 warning C4028: formal parameter 2 different from declaration

Code:

---


/*        Requests the user to input a valid file name to be scanned */
void requestFileName(FILE **fp)
{ 
        char inputFilename[30];                                // Character Array to hold the users specified input file name
        printf("Enter the name of the file to be scanned: ");       
        scanf("%s", inputFilename);                        // Scans the input file specified by the user       
        printf("\n");                                                // adds a space in between file names and file statistics       
        *fp = fopen(inputFilename, "r");        // open the file as read-only
}

/*        Stores values from the input file into the variables cityName, population, squareMileafe, pollution,
        crime, expense, and highways. */
fileScan(FILE *fp, char cityName, int population, int squareMileage, int pollution, int crime, int expense, int highways)
{ /*    BOTH ERRORS APPEAR HERE    */

        fscanf(fp, "%s %d %d %d %d %d %d", cityName, population, squareMileage, pollution, crime, expense, highways);
}

---

---

Try again, and this time pay attention: you do not have a function prototype for fileScan. Therefore your code will not work. Put a function prototype for fileScan at the top of the file, or put it in an included header file.

Code:

---

/* prototype call */

fileScan(FILE **fp, char *cityName, int population, int squareMileage,
                          int pollution, int crime, int expense, int highways);

---

Code:

---

/*  Main Call */
while(fileScan(fp, cityName, population, squareMileage, pollution, crime, expense, highways) != EOF)        // get next char from input file until we reach EOF
        {
            //...
        }

---

Code:

---

/* method */
fileScan(FILE *fp, char cityName, int population, int squareMileage, int pollution, int crime, int expense, int highways)
{ /*ERRORS: Warning 3 warning C4028: formal parameter 1 different from declaration
Warning 4 warning C4028: formal parameter 2 different from declaration */
        fscanf(fp, "%s %d %d %d %d %d %d", cityName, population, squareMileage, pollution, crime, expense, highways);
}

---

do not you see a difference?

fileScan(FILE **fp
fileScan(FILE *fp

as I said - make it return int

and actually do not forget to add return statement to the function

I put int in both my prototype call and function call and added a return statement, I no longer receive:
Warning: formal parameter 1 different from declaration,
But i do receive Warning: formal parameter 2 different from declaration.

Also I would like to thank everyone who has responded and put up with my stupidity.

Quote:

---

Originally Posted by drater

But i do receive Warning: formal parameter 2 different from declaration.

---

I was hoping you will check ALL the parameters types not only the first

Take a closer look at the definition and the prototype:

Code:

---

int fileScan(FILE** fp, char* cityName, int population, int squareMileage,
                          int pollution, int crime, int expense, int highways);

---

Code:

---

int fileScan(FILE** fp, char cityName, int population, int squareMileage,
                          int pollution, int crime, int expense, int highways);

---

See that second argument there? Something is amiss there.
Or you could just copy your entire function definition and replace the declaration with it. That will make sure they match 100%.

Alright, all my prototypes now match correctly and I no longer get any different from declaration errors. But for some reason when I compile, my program crashes after it outputs the table header (which is before my fileScan is implemented in my main)

I think we're going to need a little more code that what you've shown.
And I hope you fixed the scanf call too?

have you fixed the fscanf code to receive pointers instead of integers?

All fixed. Thank you to everyone that contributed and helped me learn more about file pointers and header files.

when doing something like this in main:

Code:

---

        /*        Checks if the last scanned livibility rating is less than the current        */
                if (&livabilityTemp < livability)
                {

                        compareInputFileValues(&livabilityTemp, livability, &cityNameTemp, cityName);
                }

---

and this as my function:

Code:

---


void compareInputFileValues(double *livabilityTemp, double livability, char *cityNameTemp[], char cityName[])
{
/*        Holds the value of the current city livibility rating in livibilityTemp,
        if the current livibility rating(livibility) is larger than the highest
        previous recording(livibilityTemp)        */
        *livabilityTemp = livability;
                       
/*        Creates a string copy of cityName if the current city livibility rating(livibility)
        is larger than the        highest previous recording of livibility(livibilityTemp)        */
        strncpy( *cityNameTemp[], cityName[], 30 );
}

---

Would the file pointers go on the temp files only?

you have no file pointers in a sample. So what you are asking again?

strncpy( cityNameTemp, cityName, 30 );

check the strncpy prototype and compare it parameters to the variable types you provide to it

I editted my previous post and added the brackets to my char arrays and added file pointers. Did i do it correctly?

I don't know how you've defined all those variables,
livabilityTemp, livability, cityNameTemp, cityName,
though they're probably in a post further back, so I can't check that right now.

However, what is the point in passing in a temp argument when you're just taking a copy of the original value?
double *livabilityTemp, double livability
If the caller needs to have a copy, it can do it itself and if compareInputFileValues needs a copy, it too, can do it by itself. There's no need for that temp variable as I see.

strncpy( *cityNameTemp[], cityName[], 30 );

This is also wrong. Remove the []. [] should only be used if you need to access an index, a subscript. But since it's empty, it won't compile.
([] can be used in arguments, as you've seen, but never in the function body code.)

I am reading from a file, and I have a number based on the set of numbers in the file. I am comparing each line for the largest number.

Code:

---

        if (&livabilityTemp < livability)
                {

                        compareInputFileValues(&livabilityTemp, livability, &cityNameTemp, cityName);
                }

---

you copy array of pointers to char into array of pointers to double using fucntion designed for copying strings. What except the crash do you want to receive as an output?

passing pointer to &cityNameTemp you will definitely NOT receive and array of pointers.

So start with showing variable declaration
Then show function calls using this vars
Then function prototypes and definitions
Then explain what these functions suppose to do

And I still do not see any file pointer.
It should be declared as

FILE* fPointer;

input/output/computation methods in separate file

Code:

---

void requestFileName(FILE **fp)
{ 
        char inputFilename[30];                                // Character Array to hold the users specified input file name
        printf("Enter the name of the file to be scanned: ");       
        scanf("%s", inputFilename);                        // Scans the input file specified by the user       
        printf("\n");                                                // adds a space in between file names and file statistics       
        *fp = fopen(inputFilename, "r");        // open the file as read-only
}



/*        Stores values from the input file into the variables cityName, population, squareMileafe, pollution,
        crime, expense, and highways. */
int fileScan(FILE *fp, char *cityName, int *population, int *squareMileage, int *pollution, int *crime, int *expense, int *highways)
{
        int fileScan = fscanf(fp, "%s %d %d %d %d %d %d", cityName, population, squareMileage, pollution, crime, expense, highways);
        return fileScan;
}

void printCityTableHighestRating(int count, char cityNameTemp[], double livabilityTemp)
{
        printf("\n");        // adds a space in between the data table and table summary
        printf("Of the %d cities, the most liveable was %s with a score of %3.2f \n",  count, cityNameTemp, livabilityTemp);
        printf("\n");        // adds a space in between the files table summary and "Press any key to continue..."       
}


/*        Compares the current cities livibility rating(livibility) with the highest scanned
        city livibility rating(livibilityTempt) and then stores the highest rating as
        well as the name of that city to be used later in a summary report */
void compareInputFileValues(double livabilityTemp, double livability, char cityNameTemp[], char cityName[])
{
/*        Holds the value of the current city livibility rating in livibilityTemp,
        if the current livibility rating(livibility) is larger than the highest
        previous recording(livibilityTemp)        */
        livabilityTemp = livability;
                       
/*        Creates a string copy of cityName if the current city livibility rating(livibility)
        is larger than the        highest previous recording of livibility(livibilityTemp)        */
        strncpy( cityNameTemp, cityName, 30 );
}

---

main:

Code:

---


while(fileScan(fp, cityName, &population, &squareMileage, &pollution, &crime, &expense, &highways) != EOF)        // get next char from input file until we reach EOF
        {


                        /*        Checks if the last scanned livibility rating is less than the current        */
                if (livabilityTemp < livability)
                {

                        compareInputFileValues(livabilityTemp, livability, cityNameTemp, cityName);
                }
        }
        printCityTableHighestRating(count, cityNameTemp, livabilityTemp);
        fclose(fp);        // close input file
}

---

I cut out some useless code in my main, for conserving space, but basically the program reads a text file filled with a city and then a bunch of numbers. It manipulates those numbers and stores them temporarily in a integer or double and then I print them out in a table like format. While I am doing this I want it to compare the last input for livability with the latest one to be scanned. If the newly scanned version is greater, it would store it as the new largest livability rating. This is so at the end of my program it can say, so-and-so-city had the best livability rating out of #of cities with a livability rating of #

if you want your compareInputFileValues to update the livabilityTemp variable it should be passed by the pointer

As I see it, you have a multitude of problems in the code. Let's start small.
I'll start with a suggestion here:

Code:

---

while(fileScan(fp, cityName, &population, &squareMileage, &pollution, &crime, &expense, &highways) != EOF)        // get next char from input file until we reach EOF
        {


                        /*        Checks if the last scanned livibility rating is less than the current        */
                if (livabilityTemp < livability)
                {

                        compareInputFileValues(livabilityTemp, livability, cityNameTemp, cityName);
                }
        }
        printCityTableHighestRating(count, cityNameTemp, livabilityTemp);
        fclose(fp);        // close input file
}

---

I don't know how you did it in the original code, but this one is just confusing. You would think the bracket in green ends the while loop, but that's not true. In this code it's redundant (read: not used), so what might be better is this:

Code:

---

        while(fileScan(fp, cityName, &population, &squareMileage, &pollution, &crime, &expense, &highways) != EOF)        // get next char from input file until we reach EOF
        {


                        /*        Checks if the last scanned livibility rating is less than the current        */
                if (livabilityTemp < livability)
                {

                        compareInputFileValues(livabilityTemp, livability, cityNameTemp, cityName);
                }
        }
        printCityTableHighestRating(count, cityNameTemp, livabilityTemp);
        fclose(fp);        // close input file

---

Less confusion.

Now, requestFileName wants to open the file the user inputs. I can understand you don't want to pass an array with the filename back, so rename the function and make sure it takes FILE** (or simply returns a FILE*) since it's going to have to pass that opened file stream back.

Now for this:

Code:

---

int fileScan = fscanf(fp, "%s %d %d %d %d %d %d", cityName, population, squareMileage, pollution, crime, expense, highways);

---

This doesn't work! You'll 99% likely to get a crash. Not to mention a warning or two.
Fscanf reads information and you must therefore pass a pointer to the variables you want it to read into. See if you can fix that.

Code:

---

void printCityTableHighestRating(int count, char cityNameTemp[], double livabilityTemp)

---

What's with the silly argument names? If it's going to print a city name, it should be named cityName and not cityNameTemp. The same goes for the last.

And as for the function

Code:

---

void compareInputFileValues(double livabilityTemp, double livability, char cityNameTemp[], char cityName[])

---

All I see is that it copies livability into livabilityTemp and cityName into cityNameTemp. In other words, the function is useless. Better to do that in the main code instead. Not to mention you aren't passing buffer sizes, so there's a good chance the function can do a buffer overrun. And that's very bad.

And as for the main code:

Code:

---

while(fileScan(fp, cityName, &population, &squareMileage, &pollution, &crime, &expense, &highways) != EOF)

---

Would you mind showing where you define all those variables?

Oh and a very important point here. I thought I already mentioned it before.

Code:

---

scanf("%s", inputFilename);

---

Never, ever read strings with scanf without specifying buffer size. Better yet, use fgets. Read my signature for more information.

Quote:

---

This doesn't work! You'll 99% likely to get a crash. Not to mention a warning or two.

---

yeah, I also thought so for a start (code is not very readable in a current state)
drater passes all needed vars as pointers so the fscanf call is OK

even it is seams to be opposite.

What can be done here - to change the names like

Code:

---

int fileScan(
                FILE*        fp,
                char*        cityName,
                int*        pPopulation,
                int*        pSquareMileage,
...
)
{
        int readItems = fscanf(fp, "%s %d %d %d %d %d %d",
                cityName, pPopulation, pSquareMileage, ...);
        return readItems;
}

---