#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];
Related
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.
I am writing a code that reads an input file of numbers, sorts them in ascending order, and prints them to output. The only thing printed to output is some really freaky symbols.
Here is my code
#include <fstream>
#include <iostream>
using namespace std;
int main()
{
int i, y, temp, num[20];
char file_nameI[21], file_nameO[21];
ofstream outfile;
ifstream infile;
cout << "Please enter name of input file: ";
cin >> file_nameI;
infile.open(file_nameI);
if (!infile)
{
cout << "Could not open input file \n";
return 0;
}
cout << "Please enter name of output file: ";
cin >> file_nameO;
outfile.open(file_nameO);
if (!outfile)
{
cout << "Could not open output file \n";
return 0;
}
for (i = 0; i < 20; i++)
{
y = i + 1;
while (y < 5)
{
if (num[i] > num[y]) //Correction3
{
infile >> temp;
temp = num[i];
num[i] = num[y];
num[y] = temp;
//y++; //Correction4
}
y++;
}
}
for (i = 0; i < 5; i++)
outfile << "num[i]:" << num[i] << "\n";
return 0;
}
Here is my input
6 7 9 0 40
Here is the output
„Ô,üþ 54
H|À°ÀzY „Ô,üþ 0
Problems with your code are already mentioned in the comments but again:
First problem is uninitialized elements of num[20] - elements of num have indeterminate values so accessing any of them triggers undefined behavior. You should first read them from the file or at least initialize them to some default value.
The part of code that should most likely do the sorting is just completely wrong. If you'd like to implement your own function for sorting, you can pick up some well-known algorithm like e.g. quicksort - but C++ Standard Library already provides sorting function - std::sort.
Besides obvious mistakes:
You are using char[] - in C++ it's almost always better to use std::string.
Your static array can only store 20 values and you are reading those from a file. You can use std::vector which can grow when you add more elements than its current capacity. It also automatically fixes the problem with uninitialized elements of num[20].
As mentioned in the comments you can organize your code and improve readability by splitting it into functions.
Here you've got it quickly rewritten. This code uses std::string instead of char[], std::vector to store the numbers and std::sort. If there is something you don't understand here, read SO documentation:
#include <fstream>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
vector<int> read_file(ifstream& in_file)
{
vector<int> vec;
int value;
while (in_file >> value)
{
vec.push_back(value);
}
return vec;
}
void write_file(ofstream& out_file, const vector<int>& values)
{
for (size_t i = 0; i < values.size(); ++i)
out_file << "value #" << i << ": " << values[i] << '\n';
}
int main()
{
string input_filename, output_filename;
ofstream out_file;
ifstream in_file;
cout << "Please enter name of input file: ";
cin >> input_filename;
in_file.open(input_filename);
if (!in_file)
{
cout << "Could not open input file\n";
return 0;
}
cout << "Please enter name of output file: ";
cin >> output_filename;
out_file.open(output_filename);
if (!out_file)
{
cout << "Could not open output file\n";
return 0;
}
auto numbers = read_file(in_file);
sort(begin(numbers), end(numbers));
write_file(out_file, numbers);
return 0;
}
You might forgot to store values in num array. Just update your code as follows and it will work.
infile.open(file_nameI);
if (!infile){
cout << "Could not open input file \n";
return 0;
} else{
i = 0;
while (infile >> num[i]){
i++;
}
}
I have two files. main.cpp:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
ifstream file;
file.open("file.txt");
if (!file.good()) {
cout << "Error." << endl;
return 1;
}
int n;
while (!file.eof()) {
file.clear();
file >> n;
if (!file.good() && !file.bad()) {
continue;
} else {
cout << "Hardware error." << endl;
break;
}
cout << n << endl;
}
file.close();
return 0;
}
and file.txt:
a 1 2 321b9 ac.de ef##g 5 #3
I'd like to read only integers from this file and write them out to the console. When file contains only integers program works well but when it contains any invalid characters then I get infinite loop. How can I fix that?
The loop is because the stream doesn't extract the character that is not an integer. You need to extract it before attempting to read another integer.
A small tweak could be all that is needed;
// on a failed read...
file.clear();
char dummy;
file >> dummy;
continue;
A side note on the use of while (!file.eof()); it is generally not recommended to do this. There are several Q&A on SO on this issue.
The problem is that file won't be read...Apparently there's a problem with an array but I don't really know how fix this issue...I'm a beginner to C++ 'arrays' and 'strings'...
My file should read the code, then translate the file, then output the text into a new file..
#include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
#include <fstream>
#include <math.h>
#include <stdio.h>
#include <string>
#include <string.h>
using namespace std;
int main()
{
// Declarations
string reply;
string inputFileName;
ifstream inputFile;
ofstream outFile;
char character;
cout << "Input file name: ";
getline(cin, inputFileName);
// Open the input file.
inputFile.open(inputFileName.c_str());
// Check the file opened successfully.
if ( ! inputFile.is_open()) {
cout << "Unable to open input file." << endl;
cout << "Press enter to continue...";
getline(cin, reply);
return 1;
}
// This section reads and echo's the file one character (byte) at a time.
while (inputFile.peek() != EOF) {
inputFile.get(character);
//cout << character;
//Don't display the file...
char cipher[sizeof(character)];
//Caesar Cipher code...
int shift;
do {
cout << "enter a value between 1-26 to encrypt the text: ";
cin >> shift;
}
while ((shift <1) || (shift >26));
int size = strlen(character);
int i=0;
for(i=0; i<size; i++)
{
cipher[i] = character[i];
if (islower(cipher[i])) {
cipher[i] = (cipher[i]-'a'+shift)%26+'a';
}
else if (isupper(cipher[i])) {
cipher[i] = (cipher[i]-'A'+shift)%26+'A';
}
}
cipher[size] = '\0';
cout << cipher << endl;
}
cout << "\nEnd of file reached\n" << endl;
// Close the input file stream
inputFile.close();
cout << "Press enter to continue...";
getline(cin, reply);
return 0;
}
To make it short: You're on c++ so just don't use the whole C stuff.
Don't use character arrays, use std::string
Don't use islower(char) but use std::islower(char,locale)
Don't use C-style arrays but std::array (compile time constant size) or std::vector (dynamic size)
You'll want to have it more like this:
#include <string>
#include <fstream>
#include <iostream>
#include <stdexcept>
#include <locale>
int main (void)
{
std::string input_filename;
std::cout << "Input file name: ";
std::getline(std::cin, input_filename);
unsigned int shift;
do
{
std::cout << "Enter a value between 1-26 to encrypt the text: ";
std::cin >> shift;
}
while ((shift == 0) || (shift > 26));
try
{
std::string filestring;
std::ifstream input(input_filename, std::ios_base::in);
if (input)
{
input.seekg(0, std::ios::end);
filestring.reserve(input.tellg());
input.seekg(0, std::ios::beg);
filestring.assign
(std::istreambuf_iterator<char>(input),
std::istreambuf_iterator<char>());
}
else
{
std::string error_string("Reading failed for: \"");
error_string.append(input_filename);
error_string.append("\"");
throw std::runtime_error(error_string);
}
std::string result;
result.reserve(filestring.size());
std::locale const loc;
for (auto character : filestring)
{
char const shifter(std::islower(character, loc) ? 'a' : 'A');
result.push_back((character-shifter+shift)%26+shifter);
}
std::cout << result << std::endl;
}
catch (std::exception & e)
{
std::cout << "Execution failed with an exception: " << std::endl;
std::cout << e.what() << std::endl;
}
}
This solution requires C++11 support. If you do not have C++11 you can replace the loop with:
size_t const N(filestring.length());
for (size_t i(0u); i<N; ++i)
{
char const shifter(std::islower(filestring[i], loc) ? 'a' : 'A');
result.push_back((filestring[i]-shifter+shift)%26+shifter);
}
From looking at your code, "character" is declared as a char which means it can only store one byte of information. Yet later on you start using it as if it was an array of characters.
You are also declare "cipher" as a char array that you manual manage like a string which is error prone. The real issue however is that you're mixing C-like code in C++. In other words, the way your code is written isn't considered idiomatic C++.
Pixelchemist already went over the important points so I'll just present a minimal refactored working example of your above code:
#include <iostream>
#include <string>
#include <fstream>
#include <stdlib.h>
using namespace std;
int main()
{
string filename;
cout << "enter input file: ";
cin >> filename;
ifstream inputFile( filename.c_str() );
string plaintext;
do
{
plaintext += inputFile.get();
}while(inputFile);
cout << plaintext << endl;
string &ciphertext = plaintext;
//Caesar Cipher code...
int shift = rand() % 26 + 1;
for(size_t i = 0; i < ciphertext.size(); ++i)
{
if (islower(ciphertext[i])) {
ciphertext[i] = (ciphertext[i] - 'a' + shift) % 26 + 'a';
}
else if (isupper(ciphertext[i])) {
ciphertext[i] = (ciphertext[i] - 'A' + shift) % 26 + 'A';
}
}
cout << ciphertext << endl;
}
You'll notice in the refactor that I've done away with char and char[] arrays altogether and replaced it with std::string. I'm also performing the cipher operation inplace on the plaintext input. This is done by making a reference alias to plaintext called ciphertext for readability. Also in my example, the shift is done randomly for prototyping but you should change it to take it as a user input instead.
You are working with a single char, thats e.g. just one letter or a number. So the whole thing with size handling is useless, because the size is always 1. You probably should use const char*. But then you can't use filestream.get() at all, because it only returns a single char (not and cstring aka const char*).
And you can use fstream.get() as condition for the loop, so you don't need to ask for the eof flag.
char my_char;
std::ifstream infstream("filename.txt");
if(!infstream.isopen())
return -1;
while(infstream.get(my_char) {
//do some stuff
}
or
std::string my_string;
std::ifstream infstream("filename.txt");
if(!infstream.isopen())
return -1;
while(infstream >> my_string) {
//do some stuff
}
for dynamic arrays in C++ use std::vector or std::list or ... one of the other STL containers, so you don't have to waste your time on memory management and using static sized arrays.
And std::string is the way to go for strings in C++. It is something similar to the STL containers, but just for char's.
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