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You are using "fread" with a variable called "output". That is a bit strange.

Did you open the file in read/write mode? Something like "w+b".

Did you call "rewind()" or "fseek()" before trying...

Hi guys,


I'm writing this to point out a problem in the partition method proposed in your tutorial about quicksort:

Quicksort - Cprogramming.com

I already wrote a message to axon, the...

Of course not. Remove that *

Please read carefully:

In your function Delete_Number() you iterate through the array with only one variable. You should use two variables; one for the reading position and another one for the writing position. They both...

johngoodman, in the line 9 of your solution, you seem to think that you are taking the number of the string and writing it in the variable num as if it was a decimal number. That is wrong. You are...

It's rather: phonebook_ptr[x].Surname

But you also have to fix the input function. It always writes in the first element of the array.

Don't write expresions at random. There is a logic reason...

It's great to see well formatted code for a change :-)

That global variable named 'counter' is a bad idea. Global variables are bad.

Your problem is that you are always passing the same pointer...

Oops, I posted this without seeing that there were more comments in another page. Sorry.

You are right Cat. I hadn't thought of that fact. The zeroes will appear together, and they can be wiped...

Oh, and if you really need to count using the numbers that start with 1, you can do it using an array. You would have one element per digit of the counter. You would increase the least significant...

The drawback of testing for zeroes (the solution proposed by others) is that sometimes it might take a lot of time to get to the next value without zeroes. For example, if you are at number...

This is what I described:



#include <stdio.h>
#include <stdlib.h>
#include <time.h>


#define DEFAULT_NUM_RECORDS 100

First, you should use the standard qsort(). Your code searches for a pair of elements to swap them, taking three assignments per swap. The most extended implementation of quicksort manages to reduce...

Then mmap() won't help, unless you want to use a raw binary file in your computer as a big cache of the database.

mmap() would be the way to go if the data were in a huge binary file instead of a...

Stable sort has some relation with this. If you use a stable sort, you can sort everything by the las column, then sort everything again by the first to last, and so on.

Though, I would recommend...

Sorry. That '1' confused me. So you are writing to descriptor 1 instead of the new file?

I don't understand the logic of your loop. You want to copy 512 bytes, but you only write if you actually...

In every iteration of the loop...

How many bytes do you read?
How many do you write?

And yes, you need to read the rules and follow them. Otherwise you will just get ignored. Most people out...

I'm reading Scott Meyers' "Effective C++, 3rd edition". I'm still with item 19, but I followed some cross references and ended up in item 46: "Define non-member functions inside templates when type...

You are right. I included inheritance in an attempt to address the most general case.

When using inheritance, you just need to write the operator<< once. I find this fact very interesting. That's...

Oh, and you might want B's print() to show the inherited part of the object by calling A's print():



class B : public A
{
public:

virtual void print (std::ostream & os) const
...

I think it's the other way around. If everything is passed by reference, my design requires no copy operations. If you put the text in a std::string and then pass it to the op<< for strings, you...

In these cases I prefer to implement the functionality in a public method (virtual, most of the times). The operator << receives a reference to the object and calls the virtual method.

Very interesting! Well, that narrows my list of real-life, good 'friend' examples (from my own experience) to... zero ;-)

Suppose that you have to write your own STL-like container. The iterators might need to access the internals of the data structure. When you implement the ++ operator, for instance, you have two...

You don't need it in any other function, and global variables are bad. Leave it local but make it static. It will live like a global variable (whole program execution lifespan, initialized only...

I think that your teacher doesn't want your program to insist in asking for a valid number.
We can't help you any further without knowing the details of your assignment. I bet that they are very...