Thread: Methods and file pointers

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%.

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?

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 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.)

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;

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.