I have hundreds of .txt files ordered by number: 1.txt, 2.txt, 3.txt,...n.txt. In each file there are two columns with decimal numbers.
I wrote an algorithm that does some operations to one .txt file alone, and now I want to recursively do the same to all of them.
This helpful question gave me some idea of what I'm trying to do.
Now I'm trying to write an algorithm to read all of the files:
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main ()
{
int i, n;
char filename[6];
double column1[100], column2[100];
for (n=1;n=200;n++)
{
sprintf(filename, "%d.txt", n);
ifstream datafile;
datafile.open(filename);
for (i=0;i<100;i++)
{
datafile >> column1[i] >> column2[i];
cout << column1[i] << column2[i];
}
datafile.close();
}
return 0;
}
What I think the code is doing: it is creating string names from 1.txt till 200.txt, then it opens files with these names. For each file, the first 100 columns will be associated to the arrays column1 and column2, then the values will be shown on the screen.
I don't get any error when compiling it, but when I run it the output is huge and simply won't stop. If i set the output to a .txt file it reaches easily some Gb!
I also tried decreasing the loop number and reduce the numbers of columns (to 3 or so), but I till get an infinite output. I would be glad if someone could point the mistakes I'm doing in the code...
I am using gcc 5.2.1 with Linux.
Thanks!
6-element array is too short to store "200.txt". It must be at least 8 elements.
The condition n=200 is wrong and is always true. It should be n<=200.
If all your files are in the same directory, you could also use boost::filesystem, e.g.:
auto path = "path/to/folder";
std::for_each(boost::filesystem::directory_iterator{path},
boost::filesystem::directory_iterator{},
[](boost::filesystem::directory_entry file){
// test if file is of the correct type
// do sth with file
});
I think this is a cleaner solution.
Related
I have a set of data in a .txt file that has an arbitrary number of columns, specified by the user in the input. I want to read that file, pick one of the columns and save it in an array. What is the best way to do this?
I have read this, this and this, but they all establish in the code the specific number of columns. I want it to be some input, so that the code is "general" and saves in that array the specific column from the input. Thank you!
EDIT: This is an example of how the input looks like - the total number of Columns (particles) is specified by the user. The output will be some other .txt of data coming from this one.
TIME PART1 PART2 PART3 PART4
0 0.0147496 934.902 0.0949583 -1192.37 0.0141576 950.604 0.0905118 -1074.44
1.66667e-005 0.0147497 2804.7 0.0949583 -3577.12 0.0141576 2851.81 0.0905117 -3223.33
3.33333e-005 0.0147497 4674.5 0.0949582 -5961.86 0.0141577 4753.02 0.0905116 -5372.21
5e-005 0.0147498 6544.3 0.094958 -8346.6 0.0141578 6654.22 0.0905115 -7521.09
6.66667e-005 0.01475 8414.09 0.0949578 -10731.3 0.0141579 8555.41 0.0905114 -9669.96
I assume the user enters the coumn number over the console. So you can use the built-in cin function to read the input. You can use for loop and string streams to get the values. Code below; although you may have tweek it a little bit as per your needs
Edit: The code below has been edited a little bit. Now it should answer your question.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
int n;
cin >>n; //user needs to input the column number
fstream newfile;
//newfile.open("file.txt",ios::out); // open the file to perform write operation using file object; Activate this function if you want to overwrite
newfile.open("file.txt",ios::in); //open the file to perform read operation using file object
if (newfile.is_open())
{
string line;
getline(newfile, line); //skipping the first line
while(getline(newfile, line))//loop throuhg rest of the lines
{
int temp=n;
while(temp != 0)//loop until you get to the requied column
{
getline(newfile, line, '\t'); //get the vaue separted by tab='\t'. Be sure that the last column also ends in '\t'
temp--;
}
cout<<line<<endl; //now line holds the element on the loop-row of the selected column
}
newfile.close(); //close the file object.
}
}
I have a text file full of names:
smartgem
marshbraid
seamore
stagstriker
meadowbreath
hydrabrow
startrack
wheatrage
caskreaver
seaash
I want to code a random name generator that will copy a specific line from the.txt file and return it.
While reading in from a file you must start from the beginning and continue on. My best advice would be to read in all of the names, store them in a set, and randomly access them that way if you don't have stringent concerns over efficiency.
You cannot pick a random string from the end of the file without first reading up that name in the file.
You may also want to look at fseek() which will allow you to "jump" to a location within the input stream. You could randomly generate an offset and then provide that as an argument to fseek().
http://www.cplusplus.com/reference/cstdio/fseek/
You cannot do that unless you do one of two things:
Generate an index for that file, containing the address of each line, then you can go straight to that address and read it. This index can be stored in many different ways, the easiest one being on a separate file, this way the original file can still be considered a text file, or;
Structure the file so that each line starts at a fixed distance in bytes of each other, so you can just go to the line you want by multiplying (desired index * size). This does not mean the texts on each line need to have the same length, you can pad the end of the line with null-terminators (character '\0'). In this case it is not recommended to work this file as a text file anymore, but a binary file instead.
You can write a separate program that will generate this index or generate the structured file for your main program to use.
All this of course, considering you want the program to run and read the line without having to load the entire file in memory first. If your program will constantly read lines from the file, you should probably just load the entire file into a std::vector<std::string> and then read the lines at will from there.
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <cstdlib>
#include <ctime>
using namespace std;
int main()
{
string filePath = "test.txt";
vector<std::string> qNames;
ifstream openFile(filePath.data());
if (openFile.is_open())
{
string line;
while (getline(openFile, line))
{
qNames.push_back(line.c_str());
}
openFile.close();
}
if (!qNames.empty())
{
srand((unsigned int)time(NULL));
for (int i = 0; i < 10; i++)
{
int num = rand();
int linePos = num % qNames.size();
cout << qNames.at(linePos).c_str() << endl;
}
}
return 0;
}
I am currently working on a small program to join two text files (similar to a database join). One file might look like:
269ED3
86356D
818858
5C8ABB
531810
38066C
7485C5
948FD4
The second one is similar:
hsdf87347
7485C5
rhdff
23487
948FD4
Both files have over 1.000.000 lines and are not limited to a specific number of characters. What I would like to do is find all matching lines in both files.
I have tried a few things, Arrays, Vectors, Lists - but I am currently struggling with deciding what the best (fastest and memory easy) way.
My code currently looks like:
#include iostream>
#include fstream>
#include string>
#include ctime>
#include list>
#include algorithm>
#include iterator>
using namespace std;
int main()
{
string line;
clock_t startTime = clock();
list data;
//read first file
ifstream myfile ("test.txt");
if (myfile.is_open())
{
for(line; getline(myfile, line);/**/){
data.push_back(line);
}
myfile.close();
}
list data2;
//read second file
ifstream myfile2 ("test2.txt");
if (myfile2.is_open())
{
for(line; getline(myfile2, line);/**/){
data2.push_back(line);
}
myfile2.close();
}
else cout data2[k], k++
//if data[j] > a;
return 0;
}
My thinking is: With a vector, random access on elements is very difficult and jumping to the next element is not optimal (not in the code, but I hope you get the point). It also takes a long time to read the file into a vector by using push_back and adding the lines one by one. With arrays the random access is easier, but reading >1.000.000 records into an array will be very memory intense and takes a long time as well. Lists can read the files faster, random access is expensive again.
Eventually I will not only look for exact matches, but also for the first 4 characters of each line.
Can you please help me deciding, what the most efficient way is? I have tried arrays, vectors and lists, but am not satisfied with the speed so far. Is there any other way to find matches, that I have not considered? I am very happy to change the code completely, looking forward to any suggestion!
Thanks a lot!
EDIT: The output should list the matching values / lines. In this example the output is supposed to look like:
7485C5
948FD4
Reading a 2 millions lines won't be too much slow, what might be slowing down is your comparison logic :
Use : std::intersection
data1.sort(data1.begin(), data1.end()); // N1log(N1)
data2.sort(data2.begin(), data2.end()); // N2log(N2)
std::vector<int> v; //Gives the matching elements
std::set_intersection(data1.begin(), data1.end(),
data2.begin(), data2.end(),
std::back_inserter(v));
// Does 2(N1+N2-1) comparisons (worst case)
You can also try using std::set and insert lines into it from both files, the resultant set will have only unique elements.
If the values for this are unique in the first file, this becomes trivial when exploiting the O(nlogn) characteristics of a set. The following stores all lines in the first file passed as a command-line argument to a set, then performs a O(logn) search for each line in the second file.
EDIT: Added 4-char-only preamble searching. To do this, the set contains only the first four chars of each line, and the search from the second looks for only the first four chars of each search-line. The second-file line is printed in its entirety if there is a match. Printing the first file full-line in entirety would be a bit more challenging.
#include <iostream>
#include <fstream>
#include <string>
#include <set>
int main(int argc, char *argv[])
{
if (argc < 3)
return EXIT_FAILURE;
// load set with first file
std::ifstream inf(argv[1]);
std::set<std::string> lines;
std::string line;
for (unsigned int i=1; std::getline(inf,line); ++i)
lines.insert(line.substr(0,4));
// load second file, identifying all entries.
std::ifstream inf2(argv[2]);
while (std::getline(inf2, line))
{
if (lines.find(line.substr(0,4)) != lines.end())
std::cout << line << std::endl;
}
return 0;
}
One solution is to read the entire file at once.
Use istream::seekg and istream::tellg to figure the size of the two files. Allocate a character array large enough to store them both. Read both files into the array, at appropriate location, using istream::read.
Here is an example of the above functions.
I have 4 days of training in C++, so bear with me.
Two data files are required to evaluate a multiple-choice examination. The first file
(booklet.dat) contains the correct answers. The total number of questions is 50. A sample
file is given below:
ACBAADDBCBDDAACDBACCABDCABCCBDDABCACABABABCBDBAABD
The second file (answer.dat) contains the students’ answers. Each line has one student
record that contains the following information:
The student’s answers (a total of 50 answers) in the same format as above (* indicates no answer)., followed by Student ID and Student Name. Example:
AACCBDBC*DBCBDAAABDBCBDBAA*BCBDD*BABDBCDAABDCBDBDA 6555 MAHMUT
CBBDBC*BDBDBDBABABABBBBBABBABBBBD*BBBCBBDBABBBDC** 6448 SINAN
ACB*ADDBCBDDAACDBACCABDCABCCBDDABCACABABABCBDBAABD 6559 CAGIL
I have a homework assignment to write a C++ program that counts the total number of correct answers by each student and outputs this information to another file called report.dat. In this file, the student’s IDs, names and scores must be given. Each correct answer is worth 1 point. For the sample files given above, the output should be as follows:
6555 MAHMUT 10
6448 SINAN 12
6550 CAGIL 49
Here's what I have so far:
include <iostream>
include <fstream>
using namespace std;
int main()
{
char booklet[50] answers[50]
int counter
// Link answers with booklet.dat
booklet = ifstream
input_file("booklet.dat");
return 0;
// Link answers with answers.dat
answers = ifstream
input_file("answer.dat");
return 0;
while (booklet==answers)
{
counter++
cout << "The student had">>counter>> "answers right";
}
}
I'm not even sure I am in the correct direction. I know I need to create an array from the file booklet.dat and another one from the file answer.dat. Then the comparison has to be made and the matches between the two have to be counted.
I don't expect anyone to do the assignment for me, i just need a nudge in the right direction.
1.) On your Syntax:
a) Each line in C++ has to end with an ";". There are some lines in your excample which don't. (Normally your compile should point at this or the following line with an error)
b) Multiple variable definitions need a "," in between two different variables.
2.) I would recommend you to use something like that:
(have a look at C++ Reference fstream)
EDIT: just a little outline, which is not complete in this form, just to give you and idea ;-)
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
int main()
{
int nr_of_students = 1000; /* Or any number you'd like to analyze */
int stud_nr[nr_of_students];
string stud_name[nr_of_students];
int stud_count[nr_of_students];
fstream in_out;
in_out.open("filename.dat",fstream::in); // fstream::in for reading from file
// fstream::out for writing to this file
if(in_out.is_open())
{
for(lines=0;(in_out>>answers && lines<nr_of_students);lines++)
{
in_out >> stud_nr[lines]; /* EDIT: sorry hat some index confusions here... */
in_out >> stud_name[lines];
stud_count[lines]=0;
for(int i=0;i<50;i++)
{
/* comparison between the booklet_array and the answers_array */
/* Count up the stud_count[lines] for each right comparison */
}
}
/* some simmilar code for the output-file */
}
else cout << "Error reading " << "filename.dat" << endl;
return 1;
}
3.) Your code would also get more performance with vectors.
A good Tutorial would be: Tutorial part I
and you find part 2 in the comments there
4.) you can achieve a more dynamic code with argc and argv**, just google for that
I hope these comments help you a little bit to carry on ;)
You are already on the right direction. Basically you want to load the answer key into an array for fast comparison and then you need to check the answers of each student and each time they get a correct answer you increment a counter and write the ID, name and score for each student. There are problems with your code such as missing semicolons.
Also please note that returning exits a function and that no statements after an unconditional return are executed, returning from main terminates your program.
The normal approach to open a file for reading is:
#include<fstream>
#include<string>
int main()
{
std::ifstream input_file("inputfilename");
// since the answer key is one line
// and each students answer , id and name are also one line
// getting that line using std::getline() would be sufficient
std::string line;
std::getline(input_file, line);
// line would now contain the entire first line except the newline character
std::getline(input_file, line);
//now line would now contain the second line in the file
return 0;
}
Writing to a file is similar we use ofstream to open a file for writing.
Like so:
#include<fstream>
int main()
{
std::ofstream output_file("outputfilename");
// lets say we have a string and an int that we want to write
std::string line_to_write("Hello File");
int number = 42;
output_file << line_to_write << number; // writes the string and then 42 on the same line
output_file << '\n'; // writes the newline character so that next writes would appear on another line
return 0;
}
For references to the standard library and C++ in general when you need to know the available functions to do something I recommend cppreference here are the specific pages on ifstream and ofstream.
good day everyone.
im having some trouble trying to figure out how to enhance my program.
here's the question:
Write a program to compute numeric grades for a course. The course records are in a file that will serve as the input file. The input file is in exactly the following format: Each line contains a student’s last name, then one space, then the student’s first name, then one space, then ten quiz scores all on one line. The quiz scores are whole numbers and are separated by one space. Your program will take its input from this file and send its output to a second file. The data in the output file will be the same as the data in the input file except that there will be one additional number (of type double) at the end of each line. This number will be the average of the student’s ten quiz scores. If this is being done as a class assignment, obtain the file names from your instructor. Use at least one function that has file streams as all or some of its arguments.
i managed to do the first part successfully. below is the code:
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <cstring>
using namespace std;
int main()
{
fstream infile("grades.txt",ios::in);
if(!infile){cerr<<"file could not be found!";exit(1);}
fstream outfile("average.txt",ios::out);
if(!outfile){cerr<<"file could not be created!";exit(1);}
char fname[20];
char lname[20];
int grades[10];
char c;
int x;
cout<<"how many students?";
cin>>x;
for(int k=0;k<x;k++)
{
infile>>fname;
infile>>lname;
for(int i=0;i<10;i++)
infile>>grades[i];
outfile<<fname<<" "<<lname<<" ";
double sum=0;
for(int j=0;j<10;j++)
{
outfile<<grades[j]<<" ";
sum+=grades[j];
}
double avg=0;
avg=sum/10;
outfile<<avg<<endl;
}
system("pause");
return 0;
}
im not able to do part (a) of the second part. i tried initializing the grades[10] array to zeros, but im not getting any correct output. any help? thank you.
Enhance the program you wrote for (Problem 10) in all the following
ways.
a-The list of quiz scores on each line will contain ten of fewer quiz
scores. (If there are fewer than ten quiz scores, that means
that the student missed one or more quizzes.) The average score is
still the sum of the quiz scores divided by 10. This amounts to
giving the student a 0 for any missed quiz.
b-The output file will contain a line (or lines) at the beginning of
the file explaining the output. Use formatting instructions to
make the layout neat and easy to read. c- After placing the desired
output in an output file, your program will close all files and then
copy the contents of the “output” file to the “input” file so
that the net effect is to change the contents of the input file.
Use at least two functions that have file streams as all or some of
their arguments. If this is being done as a class assignment,
obtain the file names from your instruction.
here's how my code looks now
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <cstring>
using namespace std;
int main()
{
fstream infile("grades.txt",ios::in);
if(!infile){cerr<<"file could not be found!";exit(1);}
fstream outfile("average.txt",ios::out);
if(!outfile){cerr<<"file could not be created!";exit(1);}
char fname[20];
char lname[20];
int grades;
int sum=0;
int linecount=0;
char c;
while(!infile.eof())
{
infile>>lname;
infile>>fname;
outfile<<lname<<" "<<fname<<" ";
for(int i=0;i<10;i++){if(infile>>grades)outfile<<grades<<" ";else {outfile<<"0 ";break;} sum+=grades;}
outfile<<double(sum/10.0);
}
system("pause");
return 0;
}
but im getting just a black space when i run the program. im not able to fix the loop to read from all the lines of the file.
As of the first part: Your code doesn't exactly solve the problem as given. The problem as given doesn't say you enter a number of students, but you should process all students in the file, no matter how many they are. Also, you neglected the part: "Use at least one function that has file streams as all or some of its arguments."
Anyways, I'd advise you to read the file line by line, and then process each line individually using ostringstream. That way, detecting that no more grades follow works the same way as detecting that no more students follow in part 1.
Hint: Look at the stream error status, especially fail, and use a while loop in part 1, and break in part 2.