c++ beginner and first time poster here.
I'm reading a file consisting of a series of large numbers separated by semicolons.
I am trying to create a loop where the file is read into two objects (first number up to semicolon in first object, second number into second object), then print the two objects containing each number. After printing the first two, it should repeat with the next two numbers until the end of the file is reached.
I have been playing around with it a lot and can't get it to work. Two problems keep occurring:
Infinite loop
failure to read the number into an object
I currently have the operator >> overloaded as follows:
std::istream& operator>>(std::istream& fin, big& obj){
char temp[size];
char stop = ';';
fin.get(temp, size, stop);
//constructor converts temp to big
obj = big(temp);
return in;
}
I have the file opening correctly, and when I just use it on one object( in>>big1) it works properly and reads the first number.
But if I try to read into two objects (in>>big1>>big2) then only the first gets a number and second gets nothing (big1==1234 big2==0).
If I try to do this in a loop which is the end goal, then I just get an infinite loop of zero. This is the basic code I have right now of what I'm trying to do:
//file opens correctly
big big1, big2;
while (!fin.eof()){
//read two numbers from file seperated by semicolon
fin >> big1 >> big2;
std::cout << big1 << "\n";
std::cout << big2 << "\n";
//repeat until end of file reached
}
fin.close();
return 0;
How can I write this so it will work? I've been trying many ways of writing it and nothing works, but it has to be possible.
Please help me if you can!
also note I can't use predefined classes like std::vector or std::string
Related
I am a young programmer who is trying to learn c++. i have a working csv.file. but i want to search for a specific number assigned to the name and then displays the name of what i'm looking for. i have the file here:
1,Bulbasaur,grass
2,Ivysaur, grass
3,Venusaur, grass
4,Charmander, fire
5,Charmeleon, fire
6,Charizard, fire
7,Squirtle, water
8,Wartortle, water
9,Blastoise, water
Code
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
ifstream ip("pokedex.csv");
string pokedexnum[9];
string pokemonName[9];
string pokemonType[9];
cout<<"please enter a pokemon number:"<<" ";
cin>>pokemonType[0];
while (ip.good()){
getline( ip, pokedexnum[0]);
getline( ip, pokemonName[0]);
getline( ip, pokemonType[0]);
}
cout<<"the pokemon that is:"<< " "<<pokedexnum[0]<< "is the pokemon called:"<< pokemonName[0];
ifstream close("pokedex.csv");
return 0;
}
when it runs
please enter a pokemon number: 1
the pokemon that is: is the pokemon called:8,Wartortle, water
could you please point out what i am doing wrong?
Among the issues in this code:
You're not using std::getline correctly for comma-separated data. The result is each pass is consuming three lines from your input file; not three values from each line.
You're also not using ip.good() correctly as a while-condition.
You're retaining your test value in the array, which will be overwritten on the first iteration pass, so it is lost.
You're ignoring potential IO failures with each std::getline invoke.
You're overwriting slot-0 in your arrays with each loop iteration.
Minor, ifstream close("pokedex.csv"); clearly isn't doing what you think it is. That just creates another fstream object called close on the given file name.
The later may be intentional for now, but clearly broken in the near future.
In reality, you don't need arrays for any of this. All you're doing is reading lines, and seem to want to test the input number against that of the CSV data first column, reporting the line that you find, then ending this.
So do that:
Read the input value to search for.
Open the file for scanning.
Enumerate the file one line at a time.
For each line from (3), use a string stream to break the line into the comma separated values.
Test the id value against the input from (1). If the same, report the result and break the loop; you're done.
The result is something like this:
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <cstdlib>
int main()
{
std::cout<<"please enter a pokemon number: ";
long num;
if (std::cin >> num && num > 0)
{
std::ifstream ip("pokedex.csv");
std::string line;
while (std::getline(ip, line))
{
std::istringstream iss(line);
std::string id, name, skill;
if (std::getline(iss, id, ',') &&
std::getline(iss, name, ',') &&
std::getline(iss, skill))
{
char *endp = nullptr;
long n = std::strtol(id.c_str(), &endp, 10);
if (id.c_str() != endp && n == num)
{
std::cout << "The pokemon that is: " << num << " is called: " << name << '\n';
break;
}
}
}
}
}
Admittedly untested, but it should work.
Whether you want to store the items in arrays at this point is entirely up to you, but it isn't needed to solve the somewhat abstract problem you seem to be attempting, namely finding the matching line and reporting the name from said-same. If you still want to store them in arrays, I suggest you craft a structure to do so, something like:
struct Pokemon
{
int id;
std::string name;
std::string skill;
};
and have a single array of those, rather than three arbitrary arrays that must be kept in sync.
Four issues jump out at me:
You store the user's input into pokemonType, but then also use pokemonType for reading data from your CSV file. The file input is going to overwrite the user input.
Your file input loop always references index 0. All of the lines from your data file are going into element 0. That's the main reason that even if the user inputs 1, the output is from the last line of the data file.
Your file reading loop is structured like you want to put one part of each data line into a different array, but what you've written actually reads three lines on every iteration, storing those lines into the three different arrays.
This isn't affecting your output, but the code ifstream close("pokedex.csv"); is written like you want to close the file stream you opened, but I do believe what this line actually does is create a new ifstream called close, and opens pokedex.csv attached to it. In other words, it's just like your other line ifstream ip("pokedex.csv"); but with close as the variable name instead of ip.
You are going to want to look into something called "string tokenization". Start with some web searches, apply what you read about to your code, and of course if you hit another snag, post a new question here to Stack Overflow, showing (as you did here) what you tried and in what way it isn't working.
Elaborating on #3, here's what how your data file is being read:
at the end of the 1st iteration of the file-reading loop, ...
pokedexnum[0] is "1,Bulbasaur,grass"
pokemonName[0] is "2,Ivysaur, grass"
pokemonType[0] is "3,Venusaur, grass"
at the end of the 2nd iteration of the file-reading loop, ...
pokedexnum[0] is "4,Charmander, fire"
pokemonName[0] is "5,Charmeleon, fire"
pokemonType[0] is "6,Charizard, fire"
at the end of the 3rd iteration of the file-reading loop, ...
pokedexnum[0] is "7,Squirtle, water"
pokemonName[0] is "8,Wartortle, water"
pokemonType[0] is "9,Blastoise, water"
And that's why
<< "is the pokemon called:"<< pokemonName[0];
outputs
is the pokemon called:8,Wartortle, water
CSCI-15 Assignment #2, String processing. (60 points) Due 9/23/13
You MAY NOT use C++ string objects for anything in this program.
Write a C++ program that reads lines of text from a file using the ifstream getline() method, tokenizes the lines into words ("tokens") using strtok(), and keeps statistics on the data in the file. Your input and output file names will be supplied to your program on the command line, which you will access using argc and argv[].
You need to count the total number of words, the number of unique words, the count of each individual word, and the number of lines. Also, remember and print the longest and shortest words in the file. If there is a tie for longest or shortest word, you may resolve the tie in any consistent manner (e.g., use either the first one or the last one found, but use the same method for both longest and shortest). You may assume the lines comprise words (contiguous lower-case letters [a-z]) separated by spaces, terminated with a period. You may ignore the possibility of other punctuation marks, including possessives or contractions, like in "Jim's house". Lines before the last one in the file will have a newline ('\n') after the period. In your data files, omit the '\n' on the last line. You may assume that the lines will be no longer than 100 characters, the individual words will be no longer than 15 letters and there will be no more than 100 unique words in the file.
Read the lines from the input file, and echo-print them to the output file. After reaching end-of-file on the input file (or reading a line of length zero, which you should treat as the end of the input data), print the words with their occurrence counts, one word/count pair per line, and the collected statistics to the output file. You will also need to create other test files of your own. Also, your program must work correctly with an EMPTY input file – which has NO statistics.
Test file looks like this (exactly 4 lines, with NO NEWLINE on the last line):
the quick brown fox jumps over the lazy dog.
now is the time for all good men to come to the aid of their party.
all i want for christmas is my two front teeth.
the quick brown fox jumps over a lazy dog.
Copy and paste this into a small file for one of your tests.
Hints:
Use a 2-dimensional array of char, 100 rows by 16 columns (why not 15?), to hold the unique words, and a 1-dimensional array of ints with 100 elements to hold the associated counts. For each word, scan through the occupied lines in the array for a match (use strcmp()), and if you find a match, increment the associated count, otherwise (you got past the last word), add the word to the table and set its count to 1.
The separate longest word and the shortest word need to be saved off in their own C-strings. (Why can't you just keep a pointer to them in the tokenized data?)
Remember – put NO NEWLINE at the end of the last line, or your test for end-of-file might not work correctly. (This may cause the program to read a zero-length line before seeing end-of-file.)
This is not a long program – no more than about 2 pages of code
Here is what I have so far:
#include<iostream>
#include<iomanip>
#include<fstream>
#include<string>
#include<cstring>
using namespace std;
void totalwordCount(ifstream &inputFile)
{
char words[100][16]; // Holds the unique words.
char *token;
int totalCount = 0; // Counts the total number of words.
// Read every word in the file.
while(inputFile >> words[99])
{
totalCount++; // Increment the total number of words.
// Tokenize each word and remove spaces, periods, and newlines.
token = strtok(words[99], " .\n");
while(token != NULL)
{
token = strtok(NULL, " .\n");
}
}
cout << "Total number of words in file: " << totalCount << endl;
}
void uniquewordCount(ifstream &inputFile)
{
char words[100][16]; // Holds the unique words
int counter[100];
char *tok = "0";
int uniqueCount = 0; // Counts the total number of unique words
while(!inputFile.eof())
{
uniqueCount++;
tok = strtok(words[99], " .\n");
while(tok != NULL)
{
tok = strtok(NULL, " .\n");
inputFile >> words[99];
if(strcmp(tok, words[99]) == 0)
{
counter[99]++;
}
else
{
words[99][15] += 1;
}
uniqueCount++;
}
}
cout << counter[99] << endl;
}
int main(int argc, char *argv[])
{
ifstream inputFile;
char inFile[12] = "string1.txt";
char outFile[16] = "word result.txt";
// Get the name of the file from the user.
cout << "Enter the name of the file: ";
cin >> inFile;
// Open the input file.
inputFile.open(inFile);
// If successfully opened, process the data.
if(inputFile)
{
while(!inputFile.eof())
{
totalwordCount(inputFile);
uniquewordCount(inputFile);
}
}
return 0;
}
I already took care of how to count the total number of words in the file in the totalwordCount() function, but in the uniquewordCount() function, I am having trouble counting the total number of unique words and counting the number of occurrences of each word. Is there anything that I need to change in the uniquewordCount() function?
This program contains several issues which are to be considered harmful! To prevent bad software being created based on entirely nonsensical assignments like the above, here are a number of hints:
Always test the stream for success after reading from it. Using in.eof() to determine if the stream is in a good state does not work! One of the problems is that you will get an infinite loop if the stream goes bad for a different reason than end of file, e.g., failure to correctly parse a value (this will set std::ios_base::failbit but not std::ios_base::eofbit.
Reading to a fixed size char array a using in >> a without having set up limits for the number of characters to be read is the C++ way to spell gets()! If you really think that using in >> a is the right way to (see next item), you absolutely need to set up the array's width, e.g., using in >> std::setw(sizeof(a)) >> a. You still need to check that this extraction was successful, of course.
From the looks of it, your teacher wants you to actually use std::istream::getline() to read the array, e.g., using in.getline(a, sizeof(a)) (which, of course, needs to be checked for success).
Note that the formatted input, i.e., in >> a already tokenizes the stream being received by spaces! There is no need to faff about with strtok() after that.
Once you have consumed a stream, it is consumed. Assuming the characters don't come from a file but rather from something like standard input, you also can't rewind the stream to read it again. I'd think you want to tokenize the values once and use them for both purposes.
This is more of a sidenote: after you created a stream, its nature should be entirely immaterial for the processing of the stream's content (although, e.g., for string streams you might want to eventually collect the result using the str() member): implement your stream processing functions in terms of std::istream rather than std::ifstream!
Since you have a concrete question ("Is there anything that I need to change in the uniquewordCount() function?"): yes, everything! Throw away this function entirely and rethink what you need to do. Basically, the structure of the functionality should be along the lines of
char buffer[100];
while (in.getline(buffer, sizeof(buffer))) {
// tokenize buffer into words
// for each word check if it already exists
// if the word does not exist, append it to the array of known words and set count to 1
// if the word exists, increment the count
// determine if the word is shorter or longer than the shortest or longest word so far
// if it is the case, remember the word's index or a pointer to it
}
It always seems to be the things that should be no problem that cause problems for me. I don't get it. :/
So I'm trying to make sure that I understand how to manipulate text files. I've got two files, "infile.txt" and "outfile.txt". "infile.txt" has six numbers in it and nothing else. Here is the code I used to manipulate the files.
#include<fstream>
using std::ifstream;
using std::ofstream;
using std::fstream;
using std::endl;
using std::ios;
int main()
{
ifstream inStream;
ofstream outStream;//create streams
inStream.open("infile.txt", ios::in | ios::out);
outStream.open("outfile.txt");//attach files
int first, second, third;
inStream >> first >> second >> third;
outStream << "The sum of the first 3 nums is " << (first+second+third) << endl;
//make two operations on the 6 numbers
inStream >> first >> second >> third;
outStream << "The sum of the second 3 nums is " << (first+second+third) << endl;
inStream.seekg(0); //4 different ways to force the program to go back to the beginning of the file
//2. inStream.seekg(0, ios::beg);
//3. inStream.seekg(0, inStream.beg);
//4. inStream.close(); inStream.open("infile.txt");
//I have tried all four of these lines and only #4 works.
//There has got to be a more natural option than just
//closing and reopening the file. Right?
inStream >> first >> second >> third;
outStream << "And again, the sum of the first 3 nums is " << (first+second+third) << endl;
inStream.close();
outStream.close();
return 0;
}
Maybe I don't understand quite how the stream works, but I've seen a few sources that said that seekg(0) should move the index back to the start of the file. Instead, this is what I get out of it.
The sum of the first 3 nums is 8
The sum of the second 3 nums is 14
And again, the sum of the first 3 nums is 14
It went back, but not nearly in the way I would have hoped. Any idea why this happened? Why did my first three attempts fail?
As Bo Persson states, it may be because your input has
encountered end of file; it shouldn't, because in C++, a text
file is defined as being terminated by a '\n', but practically
speaking, if you're working under Windows, a lot of ways of
generating a file will omit this final '\n'—although it
is formally required, practical considerations will mean that
you'll make sure that it works even if the final '\n' is
missing. And I can't think of any other reason off hand why the
seekg's wouldn't work. inStream.seekg( 0 ) is, of course,
undefined behavior, but in practice, it will work pretty much
everywhere. inStream.seekg( 0, ios::beg ) is guaranteed to
work if inStream.good(), and is, IMHO, preferable to the
first form. (The single argument form of seekg is normally
only used with the results of a tellg as an argument.) And of
course, it only works if the actual input source supports
seeking: it won't work if you're reading from a keyboard or
a pipe (but presumably, "infile.txt" is neither).
In general, you should check the status of inStream after each
read, before using the results. But if the only problem is that
the file doesn't end with '\n', it's probable that the status
will be OK (!fail()) after the final read, even if you've
encountered end of file. In which case, you'll need clear()
anyway.
Note that the above comments are valid for C++-03 and precedent.
C++11 has changed the specification of the single argument form
of seekg, and requires it to reset eofbit before anything
else. (Why is this change only for the single argument form of
seekg, and not the two argument form? Oversight?)
The second input reaches end-of-file for the stream. That state sticks until you call inStream.clear() to clear its state (in addition to the seek).
With a C++11 compliant compiler, option 4 should also work as close and reopen will now clear the previous state. Older compilers might not do that.
Try:
inStream.seekg(0, ios_base::beg);
Ok, just to be up front, this IS homework, but it isn't due for another week, and I'm not entirely sure the final details of the assignment. Long story short, without knowing what concepts he'll introduce in class, I decided to take a crack at the assignment, but I've run into a problem. Part of what I need to do for the homework is read individual characters from an input file, and then, given the character's position within its containing word, repeat the character across the screen. The problem I'm having is, the words in the text file are single words, each on a different line in the file. Since I'm not sure we'll get to use <string> for this assignment, I was wondering if there is any way to identify the end of the line without using <string>.
Right now, I'm using a simple ifstream fin; to pull the chars out. I just can't figure out how to get it to recognize the end of one word and the beginning of another. For the sake of including code, the following is all that I've got so far. I was hoping it would display some sort of endl character, but it just prints all the words out run together style.
ifstream fin;
char charIn;
fin.open("Animals.dat");
fin >> charIn;
while(!fin.eof()){
cout << charIn;
fin >> charIn;
}
A few things I forgot to include originally:
I must process each character as it is input (my loop to print it out needs to run before I read in the next char and increase my counter). Also, the length of the words in 'Animals.dat' vary which keeps me from being able to just set a number of iterations. We also haven't covered fin.get() or .getline() so those are off limits as well.
Honestly, I can't imagine this is impossible, but given the restraints, if it is, I'm not too upset. I mostly thought it was a fun problem to sit on for a while.
Why not use an array of chars? You can try it as follow:
#define MAX_WORD_NUM 20
#define MAX_STR_LEN 40 //I think 40 is big enough to hold one word.
char words[MAX_WROD_NUM][MAX_STR_LEN];
Then you can input a word to the words.
cin >> words[i];
The >> operator ignores whitespace, so you'll never get the newline character. You can use c-strings (arrays of characters) even if the <string> class is not allowed:
ifstream fin;
char animal[64];
fin.open("Animals.dat");
while(fin >> animal) {
cout << animal << endl;
}
When reading characters from a c-string (which is what animal is above), the last character is always 0, sometimes represented '\0' or NULL. This is what you check for when iterating over characters in a word. For example:
c = animal[0];
for(int i = 1; c != 0 && i < 64; i++)
{
// do something with c
c = animal[i];
}
How do i find a string in a file? In my code, i want to find the name of a person in the file. and do the actions in the comments. Here is my code:
int main(){
size_t found;
ofstream myfile;
cout << "Enter the name you wish to delete." << endl;
getline(cin, name);
myfile.open("database.dat");
found=myfile.find(name);
if (found!=string::npos){
number = myfile.tellg();
/*Delete current line and next line*/
}
}
Do you want to modify the file, or simply skip those two lines while reading?
Actually, the solution is the same for both, because removing data from the middle of the file requires reading everything after that and rewriting it with an offset (just like removing an element from the middle of an array).
So, read the entire file into memory except for any lines you determine need to be deleted (just skip those). After that, write the surviving lines back to disk. It's probably a good idea to use a temporary file which gets moved to the original name as a final step, so that data isn't destroyed if your process is aborted.