try-throw-catch

For some reason my throws are not handled. Would appreciate your help.

main()

Code:

int main()
{
	displayinfo();
	try
	{
		FileHandling operations;
		operations.ReadFile("data.txt"); //here I have the problem
		operations.CalculateValues();
		operations.printdata();
	}
	catch (int code)
	{
		cerr<<"error code number: "<<NoSuchFile<<endl;
		exit(1);
	}
	return 0;
}

The method

Code:

void FileHandling::ReadFile(const string& filename) throw(int)
{
	int numberOfRows;
	ifstream infile(filename.c_str());
	if(infile.fail()) 
		throw NoSuchFile; //this one is not handled
	infile>>numberOfRows;//get the number of records in the file
	if(!numberOfRows)
		throw numberOfRows;
	for (int i=0;i<numberOfRows;i++) //cycle through whole file
	{
		if(!infile.eof()) //check not eof()
		{
			infile.ignore(); //have to ignore \n before getline
			const int MaxLine = 80;
			char str[MaxLine];
			infile.getline(str, MaxLine);
			if(infile.fail())
				throw ErrGetLine;
			if (str[0]!='#') //if line is not comment
			{
				numRecords++;
				double number=atof(str);
				vec.push_back(number);
			}//end of if
		}
		else
			throw WrongNumberOfLinesInHeader;
	}//end of for
}//getdata

and the header file, just in case

Code:

#ifndef __FILE_HANDLING__
#define __FILE_HANDLING__

#include <vector>
#include <iostream>
using namespace std;

enum ERRORS
{
	NoSuchFile,
	numberOfRows,
	WrongNumberOfLinesInHeader,
	ErrGetLine
};

class FileHandling
{
private:
	double numRecords, sum, average, minimum, maximum;
	vector<double> vec;
public:
	FileHandling();
	void ReadFile(const string& filename) throw(int);
	void CalculateValues();
    void printdata() const;
};

#endif

Code:

enum ERRORS
{
	NoSuchFile,
	numberOfRows,
	WrongNumberOfLinesInHeader,
	ErrGetLine
};

Shouldn't "numberOfRows" be different from your local variable of that name?

All the other error codes start with upper-case, why not this one [and perhaps call it BadNumberOfRows, and check for negative numers too?]

Code:

	catch (int code)
	{
		cerr<<"error code number: "<<NoSuchFile<<endl;
		exit(1);
	}

This will print "NoSuchFile" every single time, not the code...

--
Mats

You are absolutely right. I fixed what you said. Even though, the catch still doesn't work...

The problem is probably that you are throwing something of enum type (ERRORS) but hoping to catch an int. They are not the same type.

However, it would probably be better to either throw some of the standard exceptions (which are caught by reference) or your own custom error class (derived from std::except) as you can put much more info in them.

Another thing:

Code:

#ifndef __FILE_HANDLING__
#define __FILE_HANDLING__

Identifiers beginning with underscores are reserved for compiler implementers. You shouldn't use leading underscores as you may create a conflict with a current or future compiler-specific macro. Better use something like FILENAME_H.

I should have said that I didn't actually think it would fix any real problem [at this point].

Have you tried stepping through your read function to see if it actually gets to the "throw" part?

--
Mats

Are you sure that the throw is actually being called? Perhaps put a cout statement in the if block. Did you try throwing a plain int instead of an enum?

Also, you don't initialize numberOfRows, so if the input fails, it will be some garbage number that is probably not 0, so the if (!numberOfRows) part will probably never be true.

Originally Posted by Daved

Are you sure that the throw is actually being called? Perhaps put a cout statement in the if block. Did you try throwing a plain int instead of an enum?

Also, you don't initialize numberOfRows, so if the input fails, it will be some garbage number that is probably not 0, so the if (!numberOfRows) part will probably never be true.

1) I ran it using the debugger and the throw NoSuchFile is called but not handled.
2) I did if(!numberOfRows) to examine whether there is something different rather than a number in the first line of the file such as a string or char. Won't it work?

1) So the next step would be to catch the enum type instead of an int.

2) That won't work because the numberOfRows variable will not be changed if the read fails. This is what you should do:

Code:

if (!(infile>>numberOfRows))

That will evaluate to false if the read fails to read in an integer, and so it will execute the if block and throw your exception. Note that I moved the read into the if control. Don't try to read into numberOfRows twice.

The point that Daved makes is that the integer value when attempting to read some garbage is not set at all - it is left to be whatever it happened to be.

And I think the solution to "it's thrown but not caught" is exactly what Anon says: You are throwing an enum, but you are catching an int. Whilst you and I may think that enum and int are the same thing, the compiler doesn't.

--
Mats

Originally Posted by anon

The problem is probably that you are throwing something of enum type (ERRORS) but hoping to catch an int. They are not the same type.

Solved.
You're the man! Thank you all!

Originally Posted by matsp

The point that Daved makes is that the integer value when attempting to read some garbage is not set at all - it is left to be whatever it happened to be.

So how do I verify if the user inserted an int when I ask him to instead of a char for instance?
I thought the way is

int num;
cout<<"insert a num";
cin>>num;
if(!num)
cout<<"you moron, this is not an int";

>> So how do I verify if the user inserted an int when I ask him to instead of a char for instance?

I posted while you were posting. Check out my answer in post #8 if you haven't already.

Code:

enum ERRORS
{
	NoSuchFile,
	numberOfRows,
	WrongNumberOfLinesInHeader,
	ErrGetLine
} myerrors ;

Code:

	if(infile.fail()) { 
                myerrors = NoSuchFile ;  
		throw myerrors ; 
                }

Todd

Originally Posted by Todd Burch

Code:

enum ERRORS
{
	NoSuchFile,
	numberOfRows,
	WrongNumberOfLinesInHeader,
	ErrGetLine
} myerrors ;

Code:

	if(infile.fail()) { 
                myerrors = NoSuchFile ;  
		throw myerrors ; 
                }

Todd

That will not help anything, except introduce a global variable, which I'm pretty sure isn't of any use here.

--
Mats

I don't think globals are necessary.

Code:

enum Error {SmallError, BigError };
...
throw BigError;
...
catch (Error err) {
    std::cout << "Error code: " << err << '\n';
}