I am having problems with the code bellow.
It can write fine if i kill the read section.
It can read fine if i kill the write section and the file has already been written.
The 2 don't like each other. It is like the write stream is not closed... though it should be.
What is wrong?
#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
using namespace System;
int main(array<System::String ^> ^args)
{
string a[5];
a[0]= "this is a sentence.";
a[1]= "that";
a[2]= "here";
a[3]= "there";
a[4]= "why";
a[5]= "who";
//Write some stuff to a file
ofstream outFile("data.txt"); //create out stream
if (outFile.is_open()){ //ensure stream exists
for (int i=0; i< 5; i++){
if(! (outFile << a[i] << endl)){ //write row of stuff
cout << "Error durring writting line" << endl; //ensure write was successfull
exit(1);
}
}
outFile.close();
}
//Read the stuff back from the file
if(!outFile.is_open()){ //Only READ if WRITE STREAM was closed.
string sTemp; //temporary string buffer
int j=0; //count number of lines in txt file
ifstream inFile("data.txt");
if (inFile.is_open()){
while (!inFile.eof()){
if(! (getline(inFile, sTemp)) ){ //read line into garbage variable, and ensure read of line was
if(!inFile.eof()){ //successfull accounting for eof fail condition.
cout << "Error durring reading line" << endl;
exit(1);
}
}
cout << sTemp << endl; //display line on monitor.
j++;
}
inFile.close();
}
cout << (j -1) << endl; //Print number lines, minus eof line.
}
return 0;
}
You have a memory overwrite.
You have six strings, but dimension only for five strings
string a[5];
a[0]= "this is a sentence.";
a[1]= "that";
a[2]= "here";
a[3]= "there";
a[4]= "why";
a[5]= "who";
this can cause the rest of your program have unexpected behavior.
G... bows head in shame. Was playing with file streams and wasn't paying attention to the array initializations that i rushed through.
What is interesting is that MS VS 2005 did not complain about the array value assignment a[5]= "who". It let me get away with it. So I didn't even consider that durring debugging. I can kind of see why that is ok... I wrote it out of bounds in the next contiguous spot in memory and the MS compiler let me get away with it. As far as I remember Linux does complain about this type of error. No?
Thinking it was the read file back section that was wrong i commented out all of the read section except the line ifstream inFile("data.txt"). This cause the app to crash, leading me to think the write stream was somehow not closed. I take it that the
ifstream inFile("data.txt") line alone has little to do with the array in question when the rest of the read section is commented out. Yet that is what caused it to crash in VS 2005.
At any rate, thanks!
Works fine.
Related
a bit new here, been back and forth trying to solve the issue of getline. Which I found the source of the error was due to intext[18]. Once I remove the array all errors go away. Problem is the document I have has 19 lines of data I need to retrieve so rather than typing out each string I decided to attempt to put it all in array. I am very new to c++ and this is the only time so far that I have hit a wall. I do apologize in advance if this has been solved. Ive been searching all day without resolve.
#include "pch.h"
#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>
#include <array>
using namespace std;
int main()
{
ifstream inFile;
string intext[18];
inFile.open("HW3_Data_W.txt");
while (inFile.is_open()) {
getline(inFile, intext);
cout << "Data from the file:" << endl;
cout << "Item 1: " << intext << endl;
break;
inFile.close();
}
}
You're trying to assign string value to string array variable, you should
getline(inFile, intext[i]);
where i is the number of line.
Also your array can only contain 18 lines of text, because you declared it this way. If you want to read files that have exactly 19 lines you should declare it this way:
string intext[19];
If you want your program to read any number of lines you should use std::vector.
Besides that, your while loop will only repeat once. because you break it unconditionally. I guess what you wanted to do is something like that:
inFile.open("HW3_Data_W.txt");
int i = 1;
while (inFile.is_open()) {
getline(inFile, intext[i]);
i = i + 1;
cout << "Data from the file:" << endl;
cout << "Item 1: " << intext << endl;
if(inFile.eof) continue;
inFile.close();
}
This code should work but is unnecessarily complicated. Your while condition checks if your file is open, but it will be open until you close it and you want to close it when you reach the end of the file. So your while condition look like that:
while (getline(inFile, intext[i]))
getline will return value that is convertible to false if it reaches last line of your file so your while will go until you read while file. And you have to check if file is open before your while, then you should close file after while. So something like that:
inFile.open("HW3_Data_W.txt");
int i = 0;
if(!inFile.is_open())
return EXIT_FAILURE;
while(getline(inFile, intext[i])) {
cout << "Item "<<i<<": " << intext[i] << endl;
}
inFile.close()
Some issues here:
If you have 19 lines to read, then the size of the string array should be at least 19.
Check if the file is opened successfully only once. No need to check in the while condition.
Read into consecutive elements of intext array within while using a counter which is initialized to 0 before the while loop. Increment this counter within the while loop.
Remove break from while as you want to read the whole file.
Do not close ifstream inside the while. Do it after the while loop.
This is for a homework assignment, but what I am presenting is a small test program for a chunk of my assignment.
Starting out, I am to have a list of songs in file "songs.txt". My current file looks like this.
Maneater;4;32
Whip It;2;41
Wake Me Up Before You Go-Go;3;45
The file simply contains a song title, and the duration in minutes and seconds, with the title, minutes, and seconds separated by semicolons. The full file is supposed to contain the Artists and Album as well, all separated by semicolons. Anyways, the code.
#include<iostream>
#include<cstring>
#include<fstream>
#include<cstdlib>
using namespace std;
const int CAP = 100;
const int MAXCHAR = 101;
struct songInfo
{
char title[CAP];
char durMin[CAP];
char durSec[CAP];
};
void getData(songInfo Song[], int listSize, int charSize);
int main()
{
string fileName;
songInfo Song[CAP];
ifstream inFile;
cout << "What is the file location?: ";
cin >> fileName;
inFile.open(fileName.c_str());
if (inFile.fail())
{
cout << "Cannot open file " << fileName << endl;
exit(1);
}
getData(Song, CAP, MAXCHAR);
for (int i=0;i<CAP;i++)
{
cout << Song[i].title << " - "
<< Song[i].durMin << ":"
<< Song[i].durSec << endl;
}
cout << "Press any button to continue..." << endl;
cin.get(); cin.get();
return 0;
}
void getData(songInfo Song[], int listSize, int charSize)
{
for (int i = 0; i < listSize; i++)
{
cin.get(Song[i].title, charSize, ';');
cin.get(Song[i].durMin, charSize, ';');
cin.get(Song[i].durSec, charSize, '\n');
i++;
cin.ignore();
}
}
The program compiles correctly without incident, but the output is not what I want it to be. What should happen:
Test.cpp opens songs.txt
Read the first char array into Song[i].title, delimited by ';'
Read the second char into Song[i].durMin, delimited by ';'
Read the third char into Song[i].durSec, delimited by newline
After compiling the code and running it, I get this as my output:
~/project2Test> ./test
What is the file location?: songs.txt
The program then hangs here and I have to ctrl+C out
First, what am I doing wrong?
Second, how do I go about fixing what I screwed up?
Also, as a note for class rules, I am not allowed to use any strings except for the filename. Other than that, all words must be chars.
A debugger is definitely a good thing to use for a problem like this.
Your hanging problem is occurring because in your get_data function you are using cin.get instructing your program to get input from the standard input file. You intended to use the file you defined, "inFile" not the standard input cin.
As an aside it is not clear to me why you are incrementing i twice per iteration of the for loop.
Use inFile.get() instead of cin. You need to pass inFile to the function first.
Put a print statement in the for loop to see what is happening.. A future issue that might crop up is that if you are on a Windows machine and have \r\n line endings. Unix uses \n, Windows uses \r\n
I wrote a code in C++ that writes a .txt file.
Then I want to open the code again and give some information, so I can get a new text depending on what I gave as an input.
For example I want to give the name of a month, and print in another .txt file all the lines that came after the word "November".
I found some solutions, but none of them worked for me!
One solution that I found on stack overflow is the following:
void Keyword(ifstream & stream, string token) {
string line;
while (getline(stream, line)) {
if (line.find(token) != string::npos) {
cout << line << endl;
}
}
cout << token << " not found" << endl;
}
I can't print the next lines with the code above.
Any suggestion would be helpful!
Thanks!
If you want to perform operations on files such as 'Read' and/or 'Write',you might want to search on the net(or if you have a C++ book) on topics such as "File I/O operations using C++". Anyways moving on, C++ has 2 basic classes to handle files which are ifstream and ofstream. And to use them you have to include ethier the header fstream(i.e #include<fstream>) or include them separately as #include<ifstream> and #include<ofstream>. ifstream is basically used for all input operations such as reading files etc. Similarly ofstream is used for all output operations such as writing data to files.
You can open a file and write data to it by doing the following,
ofstream myFile("filename");// Create an instance of ofstream and open file for writing data
and to write data to the file use the << operator like below,
myFile<<data;
Similarly, You can open a file and read data as follows,
ifstream myFile("filename");//Create an instance of ifstream and open file to read data
and to read data from the file use the >> operator as shown below,
myFile>>data;
You can also open a file using the method void open(const char *filename, ios::openmode mode); as shown below,
//Writing only
ofstream outFile;
outFile.open("filename.txt",ios::out);
//Reading only
ifstream inFile;
inFile.open("filename.txt",ios::in);
//For reading and writing
fstream file;
file.open("filename.txt",ios::in|ios::out);
//For closing File
outFile.close();
//or
inFile.close();
//or
file.close();
Note the open() method takes various flags such as ios::in for reading mode, ios::out for writing mode, ios::app for adding data to the end etc.
All of these can also combined by using the bit OR operator | as shown below,
outFile.open("filename.txt",ios::out|ios::app);
There is a lot more in IO. I just covered the things required to start.
Here is the solution to your problem. Try to understand it.
#include<iostream>
#include<fstream>
#include<cstring>
using namespace std;
int main()
{
ofstream outFile;
ifstream inFile;
char fileName[10],data[50];
int noLines;
cout<<"Enter Month:"<<endl;
cin>>fileName;
cout<<"Enter Number of lines you want to enter:"<<endl;
cin>>noLines;
outFile.open(fileName,ios::out);
cout<<fileName<<"(Enter Data):";
for(int i=0;i<=noLines;i++)
{
cin.getline(data,50);
outFile<<data<<endl;
}
outFile.close();
cout<<"Openening "<<fileName<<" :"<<endl;
inFile.open(fileName,ios::in);
for(int i=0 ;i<=noLines ;i++)
{
inFile.getline(data,50);
cout<<data<<endl;
}
inFile.close();
return 0;
}
OP has found most of the solution already:
string line;
while (getline(stream, line)) {
if (line.find(token) != string::npos) {
cout << line << endl;
}
}
cout << token << " not found" << endl;
But this only prints the lines with the keyword. And always prints the "not found" message. Ooops.
Instead I pitch:
string line;
bool found = false;
while (!found && getline(stream, line))
{ // search for keyword
if (line.find(token) != string::npos)
{
found = true; // found keyword. Stop looking
}
}
if (found)
{ // print out all remaining lines in the file
while (getline(stream, line))
{
cout << line << endl;
}
}
else
{
cout << token << " not found" << endl;
}
The above splits the finding of the token and the printing of the remaining file into two stages for readability. It can be compressed into one loop, but two things make this a sucker bet:
this program will be IO bound. It will spend the vast majority of its time reading the file, so little tweaks that do not address getting the file into memory are wasted time.
combining the loops would require the addition of logic to the loop that would, over along run, dwarf the minuscule cost of switching loops.
Try this:
http://www.cplusplus.com/doc/tutorial/files/
and this:
http://www.cplusplus.com/forum/beginner/14975/
It's about reading and writing files in c++ and about searching in files.
i wrote a code in C++ where it opens a .txt file and reads its contents, think of it as a (MAC address database), each mac address is delimited by a (.), my problem is after i search the file for total number of lines , iam unable to return the pointer to the initial position of the file in here i use seekg() and tellg() to manipulate the pointer to the file.
here is the code:
#include <iostream>
#include <fstream>
#include <conio.h>
using namespace std;
int main ()
{
int i = 0;
string str1;
ifstream file;
file.open ("C:\\Users\\...\\Desktop\\MAC.txt");
//this section calculates the no. of lines
while (!file.eof() )
{
getline (file,str1);
for (int z =0 ; z<=15; z++)
if (str1[z] == '.')
i++;
}
file.seekg(0,ios::beg);
getline(file,str2);
cout << "the number of lines are " << i << endl;
cout << str2 << endl;
file.close();
getchar();
return 0;
}
and here is the contents of the MAC.txt file:
0090-d0f5-723a.
0090-d0f2-87hf.
b048-7aae-t5t5.
000e-f4e1-xxx2.
1c1d-678c-9db3.
0090-d0db-f923.
d85d-4cd3-a238.
1c1d-678c-235d.
here the the output of the code is supposed to be the first MAC address but it returns the last one .
file.seekg(0,ios::end);
I believe you wanted file.seekg(0,ios::beg); here.
Zero offset from the end (ios::end) is the end of the file. The read fails and you're left with the last value you read in the buffer.
Also, once you've reached eof, you should manually reset it with file.clear(); before you seek:
file.clear();
file.seekg(0,ios::beg);
getline(file,str2);
The error would have been easier to catch if you checked for errors when you perform file operations. See Kerrek SB's answer for examples.
Your code is making all sorts of mistakes. You never check any error states!
This is how it should go:
std::ifstream file("C:\\Users\\...\\Desktop\\MAC.txt");
for (std::string line; std::getline(file, line); )
// the loop exits when "file" is in an error state
{
/* whatever condition */ i++;
}
file.clear(); // reset error state
file.seekg(0, std::ios::beg); // rewind
std::string firstline;
if (!(std::getline(file, firstline)) { /* error */ }
std::cout << "The first line is: " << firstline << "\n";
Im working on a two part program that uses an encoder do encode a text file then a decoder to decode the text file. However i cannot get my decoder to read the whole text file it just reads the first line. How do i fix this, ive played around with the loops but it is not helping me.
#include <fstream>
#include <iostream>
#include <string>
using namespace std;
int main()
{
ifstream fin;
ofstream fout;
string lineFromFile;
fin.open("secret.txt");
if (!fin.good()) throw "I/O error";
fout.open("secret.txt", ios::app);
if (!fout.good()) throw "I/O error";
while (fin.good())
{
getline(fin, lineFromFile);
for (int i = 0; i < lineFromFile.length(); i++) // for each char in the string...
lineFromFile[i]--; // bump the ASCII code by 1
fout << lineFromFile << endl;
}//while
fin.close();
fout.close();
return 0;
}
You are closing the stream in the first iteration (i.e., after reading the first line). Then you open the output stream to write the first line. Only then do you reach the end of the while-loop, at which time fin.good() cannot be true anymore since you closed fin.
The loop should contain only the reading and writing. Opening done before the loop, closing done after.
Additional suggestion: Use proper indenting, it helps understanding the control flow.
I think the problem might be that you are reading and writing from the same file: secret.txt. I do not know what the expected behaviour is but when I ran the code it was infinite, which makes some sense as you are appending.
Try changing the ouput stream, fout, to a different file name.
The while loop that currently processes the file will process a final invalid read as you do not check if getline() was successful until the loop condition. I would suggest changing to:
for (;;)
{
getline(fin, lineFromFile);
if (!fin.good())
{
break;
}
for (int i = 0; i < lineFromFile.length(); i++)
lineFromFile[i]--;
fout << lineFromFile << endl;
}
Perhaps that because another file handle,fout, accesses the file to which fin is tied, fin is closed as a side-effect. Either that, or because fout appends to the file, the file pointer is pointed to the end of the file, and so because there is no more input to read, the loop ends.
(These are hypotheses; I am not familiar enough with the specifics of C++ I.O. to conclusively say what is happening.)
If you are supposed to replace the original file with an encoded version, I recommend setting the file tied to fout to a temporary file for the duration of your code above, closing both fin and fout, and then copying the file associated with fout over the file associated with fin.
Otherwise, just tie fout to a different filename than fin, such as "encoded.txt".