I'am having a rather difficult time with this program (see code below). It is supposed to :
Create an array of 26 components to do the letter count for the 26 letters in the alphabet and a variable for the line count.
Create an ASCII (or text) file that contains text and will be used as input to my program.
Call that file "textinput" and then, have the output stored in a file called "textoutput".
Can anyone tell me what I'am doing wrong? I keep getting "File not found" errors.
#include <iostream>
#include <cstdio>
#include <iomanip>
#include <cstdlib>
#include <fstream>
using namespace std;
int main()
{
int lineCount = 0;
int letterCount[26];
for(int i = 0; i < 26; i++)
letterCount[i] = 0;
ifstream infile;
infile.open("textinput.txt", ios::in);
if(!infile)
{
cerr<<"File does not exist."<<endl;
exit(1);
}
ofstream outfile;
outfile.open("textoutput.txt", ios::out|ios::binary);
if(!outfile)
{
cerr<<"File cannot be opened."<<endl;
exit(1);
}
char data[100];
outfile<<data;
while(infile>>data)
{
outfile<<data<<endl;
}
while(infile)
{
char ch1 = infile.get();
if(ch1 == '\n')
{
lineCount++;
continue;
}
int asciiNum = (int)ch1;
if(asciiNum > 96)
{
asciiNum = asciiNum - 97;
}
else
{
asciiNum = asciiNum - 65;
}
letterCount[asciiNum]++;
}
infile.close();
outfile.close();
system("PAUSE");
return 0;
}
The funny thing is, "File not found" errors are not possible with your program.1 So, I'm going out on a limb and suggest that you need to qualify the path to your executable!
Say, you compiled with something like
gcc program1.cpp -o program1
To execute, you must use
./program1
Because program1 won't work. The reason is that with 99% certainty, your current working directory is not in the search PATH for executables (and you want to keep it that way).
Beyond this, yes, do make sure that the textinput.txt exists in the same directory.
1(There's no such error message in the program. You should know: you programmed it!)
ifstream class is used to read from files and to read from files you must need to create it first which you haven't done, so first create the file .
By doing like this :
ifstream infile;
infile.open("textinput.txt", ios::in);
you are trying to read from a file which has not been created yet OR may be as described in other answer or the comments that your file doesn't exist in the same directory.
You better use ofstream to first write on the file and then use ifstream.
Does your code work if you have the file? If it does try removing the ios::out.If i'm not mistaken ios::out is used when you do not want to truncate your old content in the file,but that implies you already have it.
Related
I want to create multiple files inside a loop and write something into them. I have made the following code. But it only creates one file named '1' instead of five files (from 1 to 5):
#include <fstream>
#include<iostream>
using namespace std;
int main(){
FILE *fp;
ofstream os;
char i;
char fileName[] = "0.txt";
for(i='1';i<='5';i++)
{
fileName[0]=i;
.
os.open (fileName);
os<<"Hello"<<"\n";
}
}
Is there anything wrong in the code? How will I get the five files?
The reference for std::ofstream::open specifically states:
Open file Opens the file identified by argument filename, associating
it with the stream object, so that input/output operations are
performed on its content. Argument mode specifies the opening mode.
If the stream is already associated with a file (i.e., it is already
open), calling this function fails.
You never close the file you're working with in your loop so open for the second-fifth time fails.
add it:
for(i='1';i<='5';i++)
{
fileName[0]=i;
os.open (fileName);
os<<"Hello"<<"\n";
os.close();
}
Also, you should check if open() succeeded:
for(i='1';i<='5';i++)
{
fileName[0]=i;
os.open (fileName);
if(os) // checks if open() succeeeded
{
os<<"Hello"<<"\n";
os.close();
}
}
#include <fstream>
#include <iostream>
using namespace std;
int main() {
ofstream os;
char fileName[] = "0.txt";
for(int i = '1'; i <= '5'; i++)
{
fileName[0] = i;
os.open(fileName);
os << "Hello" << "\n";
os.close();
}
}
I am unable to read '.dat' file. I have tired all the possible ways and tired googling it but I could not find the solution. All it gives me is a null value for integer and a junk value for a string variable or char. This what I have written
ifstream file;
file.open("data1.dat"); // I have also tried this way too like file.open("data1.dat", ios::binary, ios::in);
int data=0;
file >> data;
cout << data << endl;
system("pause");
return 0;
I am using visual studio to compile this code. I am pretty sure that the pointer is entering into the data file but I don't know for what reason the data is not being read.
The .dat file consists of integer number per line ranging from 0, so I just need to read the file and get number from each line and should find the sum of all numbers in the file. The file contains number like
5,
468,
3200,
32, etc.,. Each number is in a new line. The file can contain any number of records. this how .dat file looks when opened using a notepad editor
Your code "works" on my system.
The following compiles (without "using namespace std;")
I changed the file name for my convenience.
I created the 't391.dat' file in the same working directory of the code, and put in 10 lines, with 1 value per line, 1..9,0.
#include <fstream>
#include <iostream>
int t391a(void)
{
std::ifstream file;
file.open("t391.dat");
int data=0;
file >> data;
std::cout << data << std::endl; // echo of input / proof it works
//system("pause");
file.close();
return 0;
}
This code outputs the first value (which is all it attempts to do), so it is working!
The echo of input is good idea.
As an experiment, I temporarily renamed the 't391.dat' file to something else. The code ran to completion and printed a single 0, which is not the first value in the file. Perhaps this suggests your file is not being found, I won't guess. To confirm, I restored the file, and the above 'works' again.
Missing items in your code:
error check - file.open()
a loop to read to end of file
error check - formatted extract (i.e. read from stream) of data item
file.close - possibly not needed
If you are still working this issue, I have a minimally extended version of your code that addresses these issues. Let me know.
class ValueGet {
public:
int data;
ValueGet() {
data = 0;
}
};
int main()
{
ValueGet vg;
ifstream file;
file.open("data1.dat", fstream::binary | fstream::out); // Opens a file in binary mode for input operations i.e., getting data from file.
if (!file)
cout << "File Not Found." << endl;
else {
file.seekg(0); // To make sure that the data is read from the starting position of the file.
while (file.read((char *)&vg, sizeof(vg))) // Iterates through the file till the pointer reads the last line of the file.
cout<<vg.data<<endl;
}
//system("pause");
return 0;
}
output of the data in the file
Here is one way which I just found
#include <bits/stdc++.h>
using namespace std;
int main(){
unsigned int a;
unsigned char c;
ifstream file;
file.open("ou.bin", ios::binary);
if(!file.is_open()){
cout<<"error";
return 0;
}
for(int i=0; i<8; i++){
file>>c;
a = c;
a = a<<8;
file>>c;
a = a+ c;
cout<<a<<endl;
}
file.close();
return 0;
}
This for storing two bytes in a number you can store as many bytes in a number or even one.
Hope this helps.
You will not be able to read .dat files and understand them in your context-- they are general formats used for storing data. Unless you know the contents of it or how they are specified, you will always get junk.
I created a data file called program.txt. I need to create code that prints out number of lines and integer values from that program.txt
Heres the text I made
1
35
45
87
9
100
the program.text has these values in it
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
int main()
{
string calc;
int test;
int cool;
int book;
ifstream myfile;
ifstream outof;
myfile.open ("program.txt");
outof.open("program.txt");
if (myfile.fail())
{
cerr<<"Error Opening file"<<endl;
}
if(outof.fail ())
{
cerr<<"Error Opening file"<<endl;
}
while (!myfile.eof ())
{
getline(myfile,calc);
++book;
}
cout <<book<<endl;
while (!outof.eof ())
{
outof<<test;//
cool++;
}
cout<<cool<<endl;
myfile.close();
outof.close();
}
Also after cerr I tried exit (1) and it said exit was not defined.
I am new to this any help would be greatly appreciated. Thanks This is C++ btw.
The problem is that you are using ifstream, which stands for INPUT file stream. You want to use ofstream, which is OUTPUT file stream. You cannot write to an input file stream, hence why the << operator is not defined.
Also, rather than using exit(1) after your errors, you can just return 1; as you are inside your main function. This will terminate the program, returning 1 as the exit code.
If you really want to use exit, you need to #include <cstdlib>.
Your defined input and expected output aren't clearly defined, so I'm not sure what you're trying to do. However, here's a general idea:
Putting the filename in a fstream's constructor will automatically try to open the file for read/write. You dont need to call .open() anymore. Also, you shouldnt be reading and writing to the same file simultaneously if you dont know what you're doing.
std::ifstream myInputFile("program.txt");
std::ofstream myOutputFile("programOut.txt");
Rather than checking myInputFile.fail(), just use the overloaded boolean operator. In depth explanation: ifstream::is_open vs ifstream::fail?
if (!myInputFile) {
//Something went wrong
std::cerr << "Failed to open input file" << std::endl;
return 1;
}
Define your std::string to hold lines as you read them, read all of your input file, and count the lines.
std::string line;
int lineCount = 0;
while (getline(myInputFile,line)) {
++lineCount;
//Do something with 'line'
}
Maybe you'll need to store the lines from your input file so that you can output the count of the lines at the beginning of your output file, you might want to #include <vector> and do something like this:
std::string line;
std::vector<std::string> linesFromFile;
//Read in all lines of the input file and store them in the vector
while (getline(myInputFile, line)) {
linesFromFile.emplace_back(line);
}
//All lines read, good time to close input file
myInputFile.close();
//Print number of lines read
myOutputFile << linesFromFile.size() << std::endl;
//Loop through lines and print them
for (auto &lineFromFile : linesFromFile) {
myOutputFile << lineFromFile << std::endl;
}
//Done outputting, close output file
myOutputFile.close();
I think this should be quite simple, but my googling didn't help so far... I need to write to an existing file in C++, but not necessarily at the end of the file.
I know that when I just want to append text to my file, I can pass the flag ios:app when calling open on my stream object. However, this only let's me write to the very end of the file, but not into its middle.
I made a short program to illustrate the issue:
#include <iostream>
#include <fstream>
using namespace std;
int main () {
string path = "../test.csv";
fstream file;
file.open(path); // ios::in and ios::out by default
const int rows = 100;
for (int i = 0; i < rows; i++) {
file << i << "\n";
}
string line;
while (getline(file, line)) {
cout << "line: " << line << endl; // here I would like to append more text to certain rows
}
file.close();
}
You cannot insert in the middle of the file. You have to copy the old file to a new file and insert whatever you want in the middle during copying to the new file.
Otherwise, if you intend to overwrite data/lines in the existing file, that is possible by using std::ostream::seekp() to identify the position within the file.
You could write to the end and swap lines until it ends up in the right position.
Here's what I had to do.
Here's the test.txt file before:
12345678
12345678
12345678
12345678
12345678
Here's a sample of my program
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
fstream& goToLine(fstream& file, int line){
int charInLine = 10; //number of characters in each line + 2
//this file has 8 characters per line
int pos = (line-1)*charInLine;
file.seekg(pos);
file.seekp(pos);
return file;
}
fstream& swapLines(fstream& file, int firstLine, int secondLine){
string firstStr, secondStr;
goToLine(file,firstLine);
getline(file,firstStr);
goToLine(file,secondLine);
getline(file,secondStr);
goToLine(file,firstLine);
file.write(secondStr.c_str(),8); //Make sure there are 8 chars per line
goToLine(file,secondLine);
file.write(firstStr.c_str(),8);
return file;
}
int main(){
fstream file;
int numLines = 5; //number of lines in the file
//open file once to write to the end
file.open("test.txt",ios::app);
if(file.is_open()){
file<<"someText\n"; //Write your line to the end of the file.
file.close();
}
//open file again without the ios::app flag
file.open("test.txt");
if(file.is_open()){
for(int i=numLines+1;i>3;i--){ //Move someText\n to line 3
swapLines(file,i-1,i);
}
file.close();
}
return 0;
}
Here's the test.txt file after:
12345678
12345678
someText
12345678
12345678
12345678
I hope this helps!
Based on my basic knowledge of Operating systems, I would say it is not possible.
I mean it is not impossible to make an OS that can allow such functionality with current storage technologies, but doing so would always lead to wastage of space in segments.
But I am not aware of any technology that can allow that. Although some cloud-based DataBases do use such kinds of functionally (like inserting content in middle of a file), but they are made specifically for that DBMS software, with very specifically targeted hardware, and they may also have some custom-built kernels to perform such tasks.
I have written a program which opens a file then displays line by line its contents (text file)
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main (int argc, char* argv[])
{
string STRING;
ifstream infile;
infile.open(argv[1]);
if (argc != 2)
{
cout << "ERROR.\n";
return 1;
}
if(infile.fail())
{
cout << "ERROR.\n";
return 1;
}
else
{
while(!infile.eof())
{
getline(infile,STRING);
cout<<STRING + "\n";
}
infile.close();
return 0;
}
}
What do I need to add to make the file be read only ?
(infile.open(argv[1]) is where am guessing something goes)
The class ifstream is for reading only so, problem solved. Also, did you really mean to check argc after using argv[1] ?
On the other hand, when you use fstream you need to specify how you want to open the file:
fstream f;
f.open("file", fstream::in | fstream::out); /* Read-write. */
The default mode parameter of open for ifstream class is ios::in. That is
infile.open(argv[1]);
is same as:
infile.open(argv[1], ios::in);
So you are opening the file in read-only mode.
You already open the file for read-only. Your can't write to it if you use ifstream. Even:
infile.rdbuf()->sputc('a');
is guaranteed to fail.
You don't need to do anything as the default value for the openmode is already ios_base::in. So you're already good to go :)
See here for more details: http://en.cppreference.com/w/cpp/io/basic_ifstream/open