Misunderstood the usage of cin.unget() while handling I/O files C++ - c++

For example, I have a file named Bjarne.txt and in it there's the integers:
16 2 3 4
I have made a program to read the integers available inside the file and output them to me in the console window , however , I'm trying to use cin.unget() and by that get understanding of what it does actually , here's the source code:
#include <iostream>
#include <fstream>
using namespace std;
int main () {
ifstream ifs("Bjarne.txt");
int a;
for(int i = 0;i<4;++i){
ifs>>a;
cout<<endl<<a;
if(i==0){
ifs.unget();
}
}
And the output is:
16 6 2 3
Why is the output like that? ( it should be 16 2 3 4 ) , it only occurs when I put ifs.unget() in the program , so my questions are , what is the purpose of cin.unget() while using I/O files and why is the number 6 ( as part of 16 ) getting outputted?
Thanks in advance for any help.

Something wrong with the documentation?
Makes the most recently extracted character available again.
At the end of your first loop iteration, 6 was the last extracted character (as the final digit of the extracted formatted int with value 16).
Unget does exactly that: it un-gets it.
The next operation has the 6 to work with. So, surprise, you get 6 next time.

Related

Reading text fies with inconsistent format

I am trying to perform some operations on a text file containing a repetition of a C based string and some numbers. My code successfully carried out the operation on the first set but it would not get to the remaining sets.
Please see the content of the text file below:
Max Scherzer 2017
6.2 4 2 2 2 7
6.0 4 3 1 2 10
mod Cameron 2018
6.4 4 1 2 1 3
6.0 4 3 5 2 8
John Brandonso 2019
6.1 1 3 5 2 7
6.5 4 7 3 4 10
I have used .eof() and it completely messed up what i am doing.
#include <iostream>
#include <fstream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
char playername [25];
int season;
ifstream gamefilein;
gamefilein.open("C:\\Users\\troy\\Desktop\\GAME_SCORE\\gameinfo.txt");
if(!gamefilein)
{
cout<<"unable to open file";
}
double IP;
int H,R,ER,BB,K;
int counter=0;
double totalscore=0;
while(!gamefilein.fail())
{
gamefilein.get(playername,25);
gamefilein>>season;
cout<<playername<<season<<endl;
cout<<"Game Scores:"<<endl;
while(gamefilein>>IP>>H>>R>>ER>>BB>>K)
{
int IPa=IP;
int IPb=(IP-IPa)*10;
int IPc=0;
if(IPa>4)
{
IPc=IPa-4;
}
int score=50+(IPa*3)+(IPb*1)+(IPc*2)+(K*1)-(H*2)-(ER*4)-((R-ER)*2)-(BB*1);
cout<<score<<endl;
counter++;
totalscore+=score;
}
cout<<"Number of Games Started: "<<counter<<endl;
cout<<fixed<<setprecision(2)<<"Average Game Score:
<<(totalscore/counter)<<endl<<endl;
}
gamefilein.close();
return 0;
}
I get the below result, but I want the same result for the rest of the information in the text file, for example, I am expecting two more results like the one I have below.
Max Scherzer 2017
Game Scores:
63
64
Number of Games Started: 2
Average Game Score: 63.50
Aren't you reading the file as a char array?
If I read this correctly you try to shift an int and double over a char array with numbers in a STRING right?
e.g. "6.2" string is different than a 6.2 double number in your memory, hence why it cant work.
You also seem to have a lot of spaces which should not forget as well.
Where do you get that string to begin with? I would recommend you change the creation of that file to a more convenient format e.g. cv or json
I just solved my problem myself. The problem occurred when the loop operating on the integers and double completes its run and sees the character-based string that is in the next dataset. So i inserted a clear member function just at the point where i check for end of file
(gamefilein.clear())
and that solved my problem.
Thanks for attempting to help

Reading math equations in from file

I'm making a program where the users get a menu like this
Multiplication 1
Division 2
Subtraction 3
Addition 4
Review 5
where they can choose an option and put in the number range they want to work with and how many problems they want to do and it generates math problems for them.
That part works and I have it so when they get one wrong it puts the problem into a file math.txt using fout and that works.
What I'm trying to do now is when they choose to review it reads in the file and gives them those problems.
The file is in the format of (for example)
1 + 1 =
2 * 2 =
I'm just not sure how to read in the numbers and identify what operation it is (multiplication, addition etc.)
I've tried just getting it to read in a number with
std::ifstream fin("math.txt");
int x;
fin>>x;
But that returns 0 everytime.
So to summarize, my question is-- How can I read in a file and pull the equation (ex. 4 + 4 = \n 3 / 3 = ) so that the user can solve it?
It sounds like the problem is that you haven't flushed the previous write operation. You can either do this explicitly with flush() or close() your fout instance. Example:
std::ofstream fou("math.txt");
fou << "1 + 1 =";
// Need this: fou.close();
std::ifstream fin("math.txt");
int x;
fin >> x;
std::cout << x;
I was able to reproduce your problem when fou.close() was missing.

How to get line of numbers from file and ignore first number?

So, lets say we have a text.txt file with these numbers:
4 5 15 10 20
5 5 15 10 20 25
In the above example, the first numbers in the row describe how many numbers are in that row. The rest of the numbers are the numbers I am interested in (I will be sorting them in a later part of the code, but that is not where my question focuses).
My issue is, how can I best go about taking each row of numbers (ignoring the first number), placing them into a array, and then moving onto the next line and doing the same thing (placing them into an array, that will be later sorted)?
All my google searching points to doing this with strings via getline, and nothing really points to handling it with ints. Hope someone on here can help point me in the right direction.
Below is the basic code I would use to open the file:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
int a;
ifstream inputfile;
//declare an input file
inputfile.open("text.txt");
while(//not sure best way to do this part)
{
//guessing I can use a for loop and place numbers in array
//based on first number in the row of numbers
}
return 0;
}
The most obvious way would probably be to read a line with std::getline, then put the string into a stringstream, and read numbers from there (ignoring the first, obviously).
I suggest the following approach:
std::string line;
// Keep reading lines of text from the file.
// Break out of the loop when there are no more lines in the file.
while (getline(inputfile, line)){
// Construct a istingstream from the line of text.
std::istringstream ss(line);
// Read the numbers from the istingstream.
// Process the numbers as you please.
}

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;
}
}

PoDoFo Extract text + coords from a pdf

I have been trying for a while to use the PoDoFo C++ library to extract text and lines (with their respective coordinates). But I have no way to do this.
This is what I have so far:
#include <iostream>
#include <stdio.h>
#include <vector>
#include <podofo/podofo.h>
using namespace PoDoFo;
using namespace std;
int main( int argc, char* argv[] )
{
const char* filename = "hello.pdf";
PdfVecObjects *x = new PdfVecObjects();
PdfParser parser(x, filename);
parser.ParseFile("hello.pdf");
for (TIVecObjects obj = x->begin(); obj != x->end(); obj++){
PdfObject * a = x->RemoveObject(obj);
// THIS IS MY PROBLEM VVVVVVVVVV
cout << a->Reference().ToString() << endl;
}
return 0;
}
However, this only gives me incredibly basic information (seems to be object number)
DEBUG: Size=12
DEBUG: Reading numbers: 0 12
DEBUG: Reading XRef Section: 0 with 12 Objects.
DEBUG: Size=12
DEBUG: Reading numbers: 0 12
DEBUG: Reading XRef Section: 0 with 12 Objects.
1 0 R
2 0 R
3 0 R
4 0 R
5 0 R
6 0 R
7 0 R
8 0 R
9 0 R
10 0 R
11 0 R
I want to print out the coordinates of an object, and if it's a line or text. If it's text, I would also like to be able to print out the text. Does anyone that knows this library better than I do know what I could do to fix this?
This answer will show you how to extract the text.
To get text positioning information, you will also have to process the following commands:
Tc, Tw, Tz, TL, T*, Tr and Tm.
You definitely need to download the PDF spec from Adobe to get all the details. There is a chapter devoted entirely to text processing. It is well worth your time to print out that chapter as you will be referring to it a lot. Everything you need to know is in there, but it's not always obvious.
You will also need to use a bit of Linear Algebra. Nothing too complicated, though.
Since there are many ways to achieve the same results, it is important to implement all the commands thoroughly, even if the documents you are going to process might not seem to need certain features. For example: I ran across a document which set all text sizes to one point, which threw off all my calculations until I realized it was using the text scaling factor to set the actual font sizes.
Use the PoDoFo tools "podofotxtextract" it gives you x,y coordinate (tool folder of PoDoFo package). Extract text from Pdf.