Dealing with files thru FILE *

After doing some reading on FILE data type I decided to practice, I came up with this little program that reads any part of any file:

Code:

#include <iostream>
#include <string>
#include <stdio.h>

using namespace std;

int main()
{
    FILE * file;
    char * file_name = new char[255];
    int read_from, lenght, file_size;
    char * output;

    cout << "What file do you want to be read? ";
    cin >> file_name;

    if(!(file = fopen(file_name, "r+")))
    {
        cout << "Could not open file.";
        return 0;
    }

    fseek(file, 0, SEEK_END);
    file_size = ftell(file);
    rewind(file);

    cout << "File " << file_name << "(" << file_size << "bytes) sucessfully opened.\n\n";

    cout << "Read from offset: ";
    cin >> read_from;

    fseek(file, read_from, SEEK_SET);

    if(read_from > file_size)
    {
        cout << "Given file does not reach that far!\n";
        return 0;
    }

    cout << "How many bytes to be read? ";
    cin >> lenght;

    if((read_from + lenght) > file_size)
    {
        cout << "Given file does not reach that far!\n";
        return 0;
    }

    output = new char[lenght];

    for(int x = 0; x < lenght; x++)
    {
        output[x] = getc(file);
    }

    cout << "Output: " << output;
    return 0;
}

I'd like some suggestions, critics, tips on how to make my code better.

First, decide whether you want to program in C or C++.

> output = new char[lenght];
You also need to
- allocate space for a \0
- actually append a \0 to make it a proper string

And for both new calls, a corresponding delete call.

Not to mention closing the file when you're done.
This includes all your error paths as well (close file, memory cleanup)

First, decide whether you want to program in C or C++.

You mean, using FILE data type instead of fstream class?

> output = new char[lenght];
You also need to
- allocate space for a \0
- actually append a \0 to make it a proper string

So instead of "new char[lenght]", I would have to use something like "new char[lenght + 1]", since '\0' takes 1 byte, correct?

And for both new calls, a corresponding delete call.

Doesn't the program free memory after it's done?

Originally Posted by dhuan

Doesn't the program free memory after it's done?

No. A modern operating system would likely release all the memory allocated to the process, but relying on this leads to sloppy programming technique.

One improvement would be to spell "length" properly.

You are also prone to buffer overruns because of your C-style strings (never use cin >> with C-style strings). Suggest you switch to std::string and std::getline instead of std::cin >>.