I am having difficulty populating an array from a .txt file. I can do it without the while loop if I already know the size of the file. However, once I incorporate a while loop to extract the file size the input odes not configure correctly. Pleas take a look over my code an let me know if you see where I am going wrong.
#include "stdafx.h"
#include <iostream>
#include <cmath>
#include <string>
#include <fstream>
int main()
{
using namespace std;
const char *inName_1 = "Instance_1.txt";
const char *inName_2 = "Instance_2.txt";
int arraySize_1 = 0, arraySize_2 = 0;
int array_1[20];
int array_2[20];
int number;
ifstream A2_file_1(inName_1);
if (A2_file_1.fail())
{
cout << "File 1 not open!" << '\n';
}
while (!A2_file_1.eof())
{
arraySize_1++;
A2_file_1 >> number;
}
if (A2_file_1.is_open())
{
for (int i = 0; i < arraySize_1; i++)
{
A2_file_1 >> array_1[i];
}
A2_file_1.close();
}
cout << "The size of the array 1 is: " << arraySize_1 << endl;
for (int i = 0; i < arraySize_1; i++)
{
cout << array_1[i] << endl;
}
return 0;
}
To read an arbitrary amount of numeric values from a text-file, all you need is an std::vector and a couple of std::istreambuf_iterator objects.
Then is as simple as
std::ifstream input("Instance_1.txt");
std::vector<int> values(std::istreambuf_iterator<int>(input),
std::istreambuf_iterator<int>());
That's it. Those four lines of code (counting the empty line) will read all int values from the text file Instance_1.txt and place them into the vector values.
Related
Making a program that reads integers from a file and creates an array, I have that part completed however I am trying to figure out how to change the SIZE value depending on how many ints are in the file. This file has 15 integers but another file may have more and this array will not take in all the ints.
using namespace std;
const int SIZE = 15;
int intArray[SIZE];
void readData(istream& inFile) {
for (int i = 0; i < SIZE; i++){
inFile >> intArray[i];
cout << intArray[i] << " ";
}
}
int main() {
ifstream inFile;
string inFileName = "intValues.txt";
inFile.open(inFileName.c_str());
int value, count = 0;
while(inFile >> value){
count += 1;
}
cout << count;
readData(inFile);
return 0;
}
As you can see I have a while loop counting the number of ints in the file however when I assign that to the size value I was running into many different issues.
A fixed-sized array simply cannot be resized, period. If you need an array whose size can change at runtime, use std::vector instead.
More importantly, you are reading through the entire file just to count the number of integers, and then you are trying to read the values from where the previous loop left off. You are not seeking the ifstream back to the beginning of the file so you can re-read what you have already read.
Try something more like this instead:
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
using namespace std;
int main() {
string inFileName = "intValues.txt";
ifstream inFile(inFileName.c_str());
int value, count = 0;
while (inFile >> value){
++count;
}
cout << count;
std::vector<int> intArray;
intArray.reserve(count);
inFile.seekg(0);
while (inFile >> value){
intArray.push_back(value);
cout << value << " ";
}
// use intArray as needed...
return 0;
}
Alternatively, don't even bother counting the integers, just let the std::vector grow as needed, eg:
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
using namespace std;
int main() {
string inFileName = "intValues.txt";
ifstream inFile(inFileName.c_str());
vector<int> intArray;
int value;
while (inFile >> value){
intArray.push_back(value);
cout << value << " ";
}
// use intArray as needed...
// you an get the count from intArray.size()
return 0;
}
in my program I am attempting to input characters from a .txt file and assign them to a 2D Char array to form a Maze. The expected outcome of this code is:
xxxxxxx
xA...Bx
xxxxxxx
However I am instead warned that Column is greater than size (defined as 30) when I believe it should be 0 at the start of every loop. No matter what Column is equal to Size and im not sure why. I've included the code below. I am beginner programmer so if you have any advice could you please make it as simple as possible.
Many thanks,
Ben
#include<fstream>
#include<iostream>
#include<string>
#include <vector>
//Maze Size
#define SIZE 30
using namespace std;
void readMaze(string fileName);
void inputMaze();
int main()
{
inputMaze();
}
void readMaze(string fileName)
{
int rows;
int columns = 0;
//vector<vector<char>> maze;
char maze[SIZE][SIZE];
ifstream input(fileName);
char data;
while (input.get(data)) //While loop used to store each individual data to the string.
{
for (int rows = 0; rows < 20; rows++)
{
columns = 0;
while (data != '\n')
{
if (rows > SIZE)
{
cout << "ROWS GREATER THAN SIZE";
break;
}
else if (columns > SIZE)
{
cout << "COLUMNS GREATER THAN SIZE";
break;
}
else
{
maze[rows][columns] = data;
columns++;
data = input.get();
}
}
data = input.get();
}
}
cout << "The Maze being solved is: " << endl;
cout << maze << endl;
input.close();
}
void inputMaze()
{
string userinput;
cout << "Plese input a .txt file name" << endl;
cin >> userinput; //User inputs the name of a .txt file --> goes to readMaze()
readMaze(userinput);
}
rows is used uninitialized in readMaze so the program has undefined behavior. Also, cout << maze << endl; makes the program have undefined behavior by reading out of bounds.
Consider making maze a std::vector<std::vector<char>> or even a std::vector<std::string> to make it simpler.
Example:
#include <algorithm>
#include <fstream>
#include <iostream>
#include <iterator>
#include <sstream>
#include <string>
#include <vector>
std::vector<std::string> readMaze(std::istream& input) {
std::vector<std::string> maze;
std::string line;
while(std::getline(input, line)) { // read a complete line at a time
maze.push_back(line); // and save it in the vector
}
return maze;
}
void inputMaze() {
std::string userinput;
std::cout << "Plese input a .txt file name\n";
if(std::cin >> userinput) {
std::ifstream is(userinput);
if(is) {
auto maze = readMaze(is);
std::cout << "The Maze being solved is:\n";
std::copy(maze.begin(), maze.end(),
std::ostream_iterator<std::string>(std::cout, "\n"));
}
// the file will be closed automatically when "is" goes out of scope
}
}
int main() {
inputMaze();
}
I have this specific code to read integers from a text file:
#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
using namespace std;
bool contains_number(const string &c);
int main()
{
int from[50], to[50];
int count = 0;
{
string line1[50];
ifstream myfile("test.txt");
int a = 0;
if (!myfile)
{
cout << "Error opening output file" << endl;
}
while (!myfile.eof())
{
getline(myfile, line1[a]);
if (contains_number(line1[a]))
{
count += 1;
myfile >> from[a];
myfile >> to[a];
//cout << "from:" << from[a] << "\n";
//cout << "to:" << to[a] << "\n";
}
}
}
return 0;
}
bool contains_number(const string &c)
{
return (c.find_first_of("1:50") != string::npos);
}
I need to stock these values of from[] and to[] in 2 arrays to use them n another function, I tried to create 2 arrays in a simple way and affect the values for example:
int x[], y[];
myfile >> from[a];
for(int i=0; i<50;i++)
{
x[i] = from[i];
}
but it doesn't work. It seems that this way is only to read and display and a value in from will be deleted once another value comes.
Any help?
Thanks.
You're not incrementing your array index a in your loop. This results in line[0], to[0] and from[0] to be overwritten for every line in the file where contains_number returns true.
There is no reason for you to save your lines into memory. You can just process your lines as you go through the file (i.e. create a string line variable in your while loop).
Make sure you properly close your file handle.
Aside from that you should check your index bounds in the loop (a < 50), else you might be writing out of bounds of your arrays if your file has more numbers than 50.
A better solution yet would be to use vectors instead of arrays, especially if your file may contain any number of numbers.
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <fstream>
using namespace std;
void make_array(ifstream& num, int (&array)[50]);
int main()
{
ifstream file; // variable controlling the file
char filename[100]; /// to handle calling the file name;
int array[50];
cout << "Please enter the name of the file you wish to process:";
cin >> filename;
cout << "\n";
file.open(filename);
if (file.fail()) {
cout << "The file failed to open.\n";
exit(1);
} else {
cout << "File Opened Successfully.\n";
}
make_array(file, array);
file.close();
return (0);
}
void make_array(ifstream& num, int (&array)[50])
{
int i = 0; // counter variable
while (!num.eof() && i < 50) {
num >> array[i];
i = i + 1;
}
for (i; i >= 0; i--) {
cout << array[i] << "\n";
}
}
I am trying to read values from a file to an array using fstream. When I try to display the contents of the array, I get 2 really big negative numbers, and then the contents of the file.
Any ideas what I did wrong?
Your use of num.get(array[i]) doesn't match any of its signatures. See get method description. What you want is this:
array[i] = num.get();
As discussed in the comments, you try to read an integer which is encoded as text. For this, you need to use operator>> (which reads any type encoded as string) instead of get (which reads a single byte):
num >> array[i];
I'm a physics PhD student with some experience coding in java, but I'm trying to learn C++.
The problem I'm trying to solve is to read in data from a .txt file and then output all the numbers > 1000 in one file and all those <1000 in another.
What I need help with is writing the part of the code which actually reads in the data and saves it to an array. The data itself is only separated by a space, not all on a new line, which is confusing me a bit as I don't know how to get c++ to recognise each new word as an int. I have canabalised some code I have got from various sources online-
#include <iostream>
#include <string>
#include <fstream>
#include <cstring>
#include<cmath>
using namespace std;
int hmlines(ifstream &a) {
int i=0;
string line;
while (getline(a,line)) {
cout << line << endl;
i++;
}
return i;
}
int hmwords(ifstream &a) {
int i=0;
char c;
a >> noskipws >> c;
while ((c=a.get()) && (c!=EOF)){
if (c==' ') {
i++;
}
}
return i;
}
int main()
{
int l=0;
int w=0;
string filename;
ifstream matos;
start:
cout << "Input filename- ";
cin >> filename;
matos.open(filename.c_str());
if (matos.fail()) {
goto start;
}
matos.seekg(0, ios::beg);
w = hmwords(matos);
cout << w;
/*c = hmchars(matos);*/
int RawData[w];
int n;
// Loop through the input file
while ( !matos.eof() )
{
matos>> n;
for(int i = 0; i <= w; i++)
{
RawData[n];
cout<< RawData[n];
}
}
//2nd Copied code ends here
int On = 0;
for(int j =0; j< w; j++) {
if(RawData[j] > 1000) {
On = On +1;
}
}
int OnArray [On];
int OffArray [w-On];
for(int j =0; j< w; j++) {
if(RawData[j]> 1000) {
OnArray[j] = RawData[j];
}
else {
OffArray[j] = RawData[j];
}
}
cout << "The # of lines are :" << l
<< ". The # of words are : " << w
<< "Number of T on elements is" << On;
matos.close();
}
But if it would be easier, i'm open to starting the whole thing again, as I don't understand exactly what all the copied code is doing. So to summarise, what I need is it to-
Ask for a filepath in the console
Open the file, and store each number (separated by a space) as an element in a 1D array
I can manage the actual operations myself I think, if I could just get it to read the file the way I need.
Thanks very much
Using C++11 and the Standard Library makes your task fairly simple. This uses Standard Library containers, algorithms, and one simple lambda function.
#include <algorithm>
#include <iostream>
#include <iterator>
#include <fstream>
#include <string>
#include <vector>
int main()
{
std::string filename;
std::cout << "Input filename- ";
std::cin >> filename;
std::ifstream infile(filename);
if (!infile)
{
std::cerr << "can't open " << filename << '\n';
return 1;
}
std::istream_iterator<int> input(infile), eof; // stream iterators
std::vector<int> onvec, offvec; // standard containers
std::partition_copy(
input, eof, // source (begin, end]
back_inserter(onvec), // first destination
back_inserter(offvec), // second destination
[](int n){ return n > 1000; } // true == dest1, false == dest2
);
// the data is now in the two containers
return 0;
}
Just switch the type of variable fed to your fistream, created from new std:ifstream("path to file") into a int and c++ will do the work for you
#include <fstream> //input/output filestream
#include <iostream>//input/output (for console)
void LoadFile(const char* file)
{
int less[100]; //stores integers less than 1000(max 100)
int more[100]; //stores integers more than 1000(max 100)
int numless = 0;//initialization not automatic in c++
int nummore = 0; //these store number of more/less numbers
std::ifstream File(file); //loads file
while(!file.eof()) //while not reached end of file
{
int number; //first we load the number
File >> number; //load the number
if( number > 1000 )
{
more[nummore] = number;
nummore++;//increase counter
}
else
{
less[numless] = number;
numless++;//increase counter
}
}
std::cout << "number of numbers less:" << numless << std::endl; //inform user about
std::cout << "number of numbers more:" << nummore << std::endl; //how much found...
}
This should give you an idea how should it look like(you shoudnt use static-sized arrays tough) If you got any probs, comment back
Also, please try to make nice readable code, and use tabs/ 4 spaces.
even though its pure C, this might give you some hints.
#include <stdio.h>
#include <stdlib.h>
#include "string.h"
#define MAX_LINE_CHARS 1024
void read_numbers_from_file(const char* file_path)
{
//holder for the characters in the line
char contents[MAX_LINE_CHARS];
int size_contents = 0;
FILE *fp = fopen(file_path, "r");
char c;
//reads the file
while(!feof(fp))
{
c = fgetc(fp);
contents[size_contents] = c;
size_contents++;
}
char *token;
token = strtok(contents, " ");
//cycles through every number
while(token != NULL)
{
int number_to_add = atoi(token);
//handle your number!
printf("%d \n", number_to_add);
token = strtok(NULL, " ");
}
fclose(fp);
}
int main()
{
read_numbers_from_file("path_to_file");
return 0;
}
reads a file with numbers separated by white space and prints them.
Hope it helps.
Cheers