Moving through text file c++ - c++

I'm trying to save numbers from first txt file to second one in reversed order.
To be clear, inside 1st txt I have typed numbers from 1 to 10 (decimal notation). When I try to count them, I get 5 or 7, depending on what's between them (space or enter).
Then, another error is that inside 2nd txt program saves as much "0s" as dl's variable value is equal to instead of loaded numbers in reversed order.
I paste the whole code, because I don't know file operation rules good enough to determine which exact part could be the source of problem. Thank You in advance.
#include <fstream>
#include <iostream>
using namespace std;
int main() {
fstream plik1;
plik1.open("L8_F3_Z2a.txt", ios::in | ios::binary);
fstream plik2;
plik2.open("L8_F3_Z2b.txt", ios::out);
if(!plik1.good() || !plik2.good()) {
cout << "file(s) invalid" << endl;
return 1;
}
plik1.seekg(0, ios::end);
int dl = plik1.tellg() / sizeof(int);
cout << "length = " << dl << endl;
int a;
for(int i = 0; i < dl; i++) {
plik1.seekg((i + 1) * sizeof(int), ios::end);
plik1 >> a;
plik2 << a;
cout << i + 1 << ". a = " << a << endl;
}
plik1.close();
plik2.close();
return 0;
}
edit the output is:
length = 7
1. a = 0
2. a = 0
3. a = 0
4. a = 0
5. a = 0
6. a = 0
7. a = 0
--------------------------------
Process exited after 0.03841 seconds with return value 0
Press any key to continue . . .

Problem
When a file is encoded as text the binary size of the data is irrelevant.
int dl = plik1.tellg() / sizeof(int);
will get you the side of the file in integers, but the file isn't storing integers. It is storing a stream of characters. Say for example the file holds one number:
12345
which is five characters long. Assuming the file is using good ol ASCII, that's 5 bytes. When 12345 is converted to an int it will probably be 4 or 8 bytes and almost certainly not 5 bytes. Assuming the common 32 bit (4 byte) int
int dl = plik1.tellg() / sizeof(int);
int dl = 5 / 4;
int dl = 1;
Yay! It worked! But only by the grace of whatever deity or cosmic entity you worship. Or don't worship. I'm not going to judge. To show why you can't count on this, lets look at
123
this is three characters and 3 bytes, so
int dl = plik1.tellg() / sizeof(int);
int dl = 3 / 4;
int dl = 0;
Whoops.
Similarly
1 2 3 4 5
is five numbers. The file length will probably be the sum of one byte per digit and one byte per space, 9 bytes.
Where this gets weird is some systems, looking at you Windows, use a two character end of line marker, carriage return and a line feed. This means
1
2
3
4
5
will sum up to 13 bytes.
This is why you see a different size depending on whether the numbers are separated with spaces or newlines.
Solution
The only way to find out how many numbers are in the file is to read the file, convert the contents to numbers, and count the numbers as you find them.
How to do that:
int num;
int count = 0;
while (plik1 >> num) // read numbers until we can't read any more
{
count++;
}
From this you can determine the size of the array you need. Then you rewind the file, seek back to the beginning, allocate the array and read the file AGAIN into the array. This is dumb. File IO is painfully slow. You don't want to do it twice. You want to read the file once and store as you go without caring how many numbers are in the file.
Fortunately there are a number of tools built into C++ that do exactly that. I like std::vector
std::vector<int> nums;
int num;
while (plik1 >> num)
{
nums.push_back(num);
}
vector even keeps count for you.
Next you could
std::reverse(nums.begin(), nums.end());
and write the result back out.
for (int num: nums)
{
plik2 << num << ' ';
}
Documentation for std::reverse
If your instructor has a no vector policy, and unfortunately many do, your best bet is to write your own simple version of vector. There are many examples of how to do this already on Stack Overflow.
Addendum
In binary 5 integers will likely be 20 or 40 bytes no matter how many digits are used and no separators are required.
It sounds like storing data as binary is the bees knees, right? Like it's going to be much easier.
But it's not. Different computers and different compilers use different sizes for integers. All you are guaranteed is an int is at least 2 bytes and no larger than a long. All of the integer types could be exactly the same size at 64 bits. Blah. Worse, not all computers store integers in the same order. Because it's easier to do some operations if the number is stored backwards, guess what? Often the number is stored backwards. You have to be very, very careful with binary data and establish a data protocol (search term for more on this topic: Serialization) that defines the how the data is to be interpreted by everyone.

Related

Time limit exceeded on test 10 code forces

hello i am a beginner in programming and am in the array lessons ,i just know very basics like if conditions and loops and data types , and when i try to solve this problem.
Problem Description
When Serezha was three years old, he was given a set of cards with letters for his birthday. They were arranged into words in the way which formed the boy's mother favorite number in binary notation. Serezha started playing with them immediately and shuffled them because he wasn't yet able to read. His father decided to rearrange them. Help him restore the original number, on condition that it was the maximum possible one.
Input Specification
The first line contains a single integer n (1⩽n⩽105) — the length of the string. The second line contains a string consisting of English lowercase letters: 'z', 'e', 'r', 'o' and 'n'.
It is guaranteed that it is possible to rearrange the letters in such a way that they form a sequence of words, each being either "zero" which corresponds to the digit 00 or "one" which corresponds to the digit 11.
Output Specification
Print the maximum possible number in binary notation. Print binary digits separated by a space. The leading zeroes are allowed.
Sample input:
4
ezor
Output:
0
Sample Input:
10
nznooeeoer
Output:
1 1 0
i got Time limit exceeded on test 10 code forces and that is my code
#include <iostream>
using namespace std;
int main()
{
int n;
char arr[10000];
cin >> n;
for (int i = 0; i < n; i++) {
cin >> arr[i];
}
for (int i = 0; i < n; i++) {
if (arr[i] == 'n') {
cout << "1"
<< " ";
}
}
for (int i = 0; i < n; i++) {
if (arr[i] == 'z') {
cout << "0"
<< " ";
}
}
}
Your problem is a buffer overrun. You put an awful 10K array on the stack, but the problem description says you can have up to 100K characters.
After your array fills up, you start overwriting the stack, including the variable n. This makes you try to read too many characters. When your program gets to the end of the input, it waits forever for more.
Instead of putting an even more awful 100K array on the stack, just count the number of z's and n's as you're reading the input, and don't bother storing the string at all.
According to the compromise (applicable to homework and challenge questions) described here
How do I ask and answer homework questions?
I will hint, without giving a code solution.
In order to fix TLEs you need to be more efficient.
In this case I'd start by getting rid of one of the three loops and of all of the array accesses.
You only need to count two things during input and one output loop.

Reading a file of number into an array while skipping first two values every 1026 entries

I am trying to read in a text file of numbers in which there are 2 values in the beginning that I do not care about, followed by 1024 values that I do care about. The file has approximately 100000 entries that I need to do a calculation on every 1024 of them. The format is something like
1
1025
3000
3572
3579
4023
3593
2930
.
.
.
1
1025
.
.
.
So basically the 1 and the 1025 are header values describing the data set which I need to ignore, then I need to read every value after those header values into an array so I can then run calculations on the values in the array. I was thinking of using while(!file.eof()) but I can not think of how to have the code skip those two numbers while it reads through the 100000 entries. I am pretty new to c++, I usually use GUI's to do my data analysis, but I am on a project that is requiring me to us C++, so I'm really out of my comfort zone here. I appreciate any help I can get.
There are a lot of ways you can do it. The most straight forward example I could think of was:
#include <iostream>
#include <string>
int main()
{
int i = 0;
std::string s;
while( std::cin >> s )
{
if( i++ < 2 ) continue;
std::cout << s;
if( i == 1024 ) i = 0;
}
}

Storing file data variables in a dimentional array

I have a .txt file which I'm trying to gather data from, that can then be used within variables within my code to be used in other functions.
Here's an example of my text file:
0 10 a namez 1 0
0 11 b namea 1 1
1 12 c nameb 1 1
2 13 d namec 0 1
3 14 e named 1 1
So my file will not always be the same number of lines, but always the same number of variables per line.
I currently have this, to firstly get the length of the file and then change the amount of rows within the array:
int FileLength()
{
int linecount = 0;
string line;
ifstream WorkingFile("file.txt");
while(getline(WorkingFile, line))
{
++linecount;
}
return linecount;
}
int main()
{
string FileTable [FileLength()][6];
}
Firstly I don't know if the above code is correct or how I can add the values from my file into my FileTable array.
Once I have my FileTable array with all the file data in it, I then want to be able to use this in other functions.
I've been able to do:
if(FileTable[2][0] = 1)
{
cout << "The third name is: " << FileTable[2][3] << endl;
}
I understand my code may not make sense here but I hope it demonstrates what I'm attempting to do.
I have to do this for a larger text file and all the 6 variables per line relate to be input to a function.
Hold each line in its own object, this is much clearer:
struct Entry
{
std::array<std::string, 6> items; // or a vector
};
In main:
std::vector<Entry> file_table( FileLength() );
Note that it is a waste of time to read the whole file first in order to find the number of entries. You could just start with an empty vector, and push in each entry as you read it.
Your access code:
if( file_table.size() > 2 && file_table[2].items[0] == "1" )
{
cout << "The third name is: " << FileTable[2].items[2] << endl;
}
I would actually recommend giving the members of Entry names, instead of just having an array of 6 of them. That would make your code more readable. (Unless you really need to iterate over them, in which case you can use an enum for the indices).
You could define an operator[] overload for Entry if you don't like the .items bit.
since the number of lines is dynamic I suggest to use vector instead of array. you can push back your data to the vector line by line until you read eof.
also try to study about OOP a little , it would make your code more understandable.
take look at these:
http://www.cplusplus.com/reference/vector/vector/
http://www.geeksforgeeks.org/eof-and-feof-in-c/

Using stringstream to indent/center output

I'm learning c++ and got the project to send a pascal's triangle to output (after n-rows of calculation)., getting output like this, stored in a stringstream "buffer"
1
1 1
1 2 1
1 3 3 1
But what I want is rather
1
1 1
1 2 1
1 3 3 1
My idea was: calculate the difference of the last line and current line length (I know that the last one is the longest). Then pad each row using spaces (half of the line-length-difference).
My Problem now is:
I didn't get how getLine works, neither how I might extract a specific (-> last) line
I don't know and could not find how to edit one specific line in a stringstream
Somehow I got the feeling that I'm not on the best way using stringstream.
So this is rather a common question: How'd you solve this problem and if possible with stringstreams - how?
To know the indentation of the first line, you would need to know the number of lines in the input. Therefore you must first read in all of the input. I chose to use a vector to store the values for the convenience of the .size() member function which will give the total number of lines after reading in all input.
#include<iostream>
#include<sstream>
#include<vector>
#include<iomanip> // For setw
using namespace std;
int main()
{
stringstream ss;
vector<string> lines;
string s;
//Read all of the lines into a vector
while(getline(cin,s))
lines.push_back(s);
// setw() - sets the width of the line being output
// right - specifies that the output should be right justified
for(int i=0,sz=lines.size();i<sz;++i)
ss << setw((sz - i) + lines[i].length()) << right << lines[i] << endl;
cout << ss.str();
return 0;
}
In this example, I am using setw to set the width of the line to be right justified. The padding on the left side of the string is given by (sz - i) where sz is the total number of lines and i is the current line. Therefore every subsequent line has 1 less space on the left hand side.
Next I need to add in the original size of the line (lines[i].length()), otherwise the line will not contain a large enough space for the resulting string to have the correct padding on the left hand side.
setw((sz - i) + lines[i].length())
Hope this helps!
If you have access to the code that writes the initial output, and if you know the number of lines N you are writing, you could simply do:
for(int i = 0; i < N; ++i) {
for(int j = 0; j < N - 1 - i; ++j)
sstr << " "; // write N - 1 - i spaces, no spaces for i == N.
// now write your numbers the way you currently do
}

Getting input from external files?

I need to get very basic input from an external file in C++. I tried searching the internet a few times but nothing really applied to what I need. This would be a .txt file that the input it coming from, and it would be filled with lines like this:
131
241
371
481
I have code already to manually get this input, and it looks like this:
using namespace std;
//Gets the initial values from the user.
int control=0;
while (rowb!=0){
cout << "Row: ";
cin >> rowb;
cout << "Column: ";
cin >> columnb;
cout << "Number: ";
cin >> numb;
row[control]=rowb-1;
column[control]=columnb-1;
num[control]=numb;
control++;
}
This is part of a program that solves sudoko boards. The inputed numbers are the initial values that a sudoko board holds, and the user is inputing the row, column, and number that comes from a board.
What I need is to be able to create a .txt file with these numbers stored in rows so that I do not have to enter so many numbers. I have very little idea how to go about doing this. Mainly I'll only be using the txt file for testing my program as I move along with adding more code to it. It takes 150+ entered numbers within my program just to get a single board, and it takes a lot of time. Any accidentally wrong entered value is also a huge problem as I have to start again. So how would I get C++ to read a text file and use those numbers as input?
Aside from the other suggestions, you can simply redirect a file to standard input, like so (where $ is the command prompt):
$ myprogram < mytextfile.txt
That will run myprogram just as normal but take input from mytextfile.txt as if you had typed it in. No need to adjust your own program at all.
(This works on both Unix/Linux systems and on Windows.)
You can open a file for input with std::ifstream from the header <fstream>, then read from it as you would from std::cin.
int main()
{
std::ifstream input("somefile.txt");
int a;
input >> a; // reads a number from somefile.txt
}
Obviously, you can use >> in a loop to read multiple numbers.
Create an std::ifstream object, and read from it just like you would from std::cin. At least if I understand what you're trying to do, the 131 as the first input is really intended to be three separate numbers (1, 3, and 1). If so, it's probably easiest to change your input file a bit to put a space between each:
1 3 1
2 4 1
3 7 1
4 8 1
Personally, I would start with a different format of the file: enter a value for each cell. That is, each row in the input file would represent a row in the sudoko board. Empty fields would use a space character. The immediate advantage is that the input actually pretty much looks like the sudoko board. Also, you would enter at most 90 characters: 9 characters for the board and a newline for each line:
#include <iostream>
#include <fstream>
#include <algorithm>
#include <iterator>
int main(int ac, char* av[])
{
std::ifstream in(ac == 1? "sudoko.init": av[1]);
char board[9][9];
for (int i(0); i != 9; ++i)
{
in.read(board[i], 9).ignore();
}
if (!in)
{
std::cout << "failed to read the initial board\n";
}
else
{
typedef std::ostream_iterator<char> iterator;
std::fill_n(iterator(std::cout << "board:\n\n+", "+"), 9, '=');
for (int i(0); i != 9; ++i)
{
std::copy(board[i] + 0, board[i] + 9, iterator(std::cout << "\n|", "|"));
std::fill_n(iterator(std::cout << "\n+", "+"), 9, (i + 1) % 3? '-': '=');
}
std::cout << "\n";
}
}
This would take input like this:
4 5 3 8
71 3
16 7
6 4 7
6 8
1 9 5
6 42
5 94
4 7 9 3
Note that each of these lines uses 9 characters. You might want to use something more visible like ..