I wrote a quick C++ program that asks the user for a input text file and an output text file. The program is then supposed to number the lines in the file on the left margin. However, I cannot seem to get it working properly, it compiles fine but does not number the lines like it is supposed to. I believe it is a logical error on my part. I am also not too familiar with file i/o in C++ as I am just learning it now using old school textbooks.
Here is the file:
#include <iostream>
#include <fstream>
#include <string>
#include <cassert>
#include <cstdio>
using namespace std;
int main(void)
{int i = 0 , num = 1;
string inputFileName;
string outputFileName;
string s;
ifstream fileIn;
ofstream fileOut;
char ch;
cout<<"Enter name of input file: ";
cin>>inputFileName;
cout<<"Enter name of output file: ";
cin>>outputFileName;
fileIn.open(inputFileName.data());
fileOut.open(outputFileName.data());
assert(fileIn.is_open() );
assert(fileOut.is_open() );
while (!(fileIn.eof()))
{ch=fileIn.get();
if (ch=='\n') num++;
fileOut << num << "\n";
s.insert(i,1,ch); //insert character at position i
i++;
}
fileOut << s;
fileIn.close();
fileOut.close();
return 0;
}
If anyone could point me in thr right direction or give me some tips I would be eternally grateful.
int i = 0;
string line;
while (getline(infile, line))
{
outfile << (i++) << " " << line << "\n";
}
Related
i want to receive an input from user and search a file for that input. when i found a line that includes that specific word, i want to print it and get another input to change a part of that line based on second user input with third user input. (I'm writing a hospital management app and this is a part of project that patients and edit their document).
i completed 90 percent of the project but i don't know how to replace it. check out following code:
#include <iostream>
#include <stream>
#include <string.h>
#include <string>
using namespace std;
int main(){
string srch;
string line;
fstream Myfile;
string word, replacement, name;
int counter;
Myfile.open("Patientlist.txt", ios::in|ios::out);
cout << "\nEnter your Name: ";
cin.ignore();
getline(cin, srch);
if(Myfile.is_open())
{
while(getline(Myfile, line)){
if (line.find(srch) != string::npos){
cout << "\nYour details are: \n" << line << endl << "What do you want to change? *type it's word and then type the replacement!*" << endl;
cin >> word >> replacement;
}
// i want to change in here
}
}else
{
cout << "\nSearch Failed... Patient not found!" << endl;
}
Myfile.close();
}
for example my file contains this line ( David , ha , 2002 ) and user wants to change 2002 to 2003
You cannot replace the string directly in the file. You have to:
Write to a temporary file what you read & changed.
Rename the original one (or delete it if you are sure everything went fine).
Rename the temporary file to the original one.
Ideally, the rename part should be done in one step. For instance, you do not want to end up with no file because the original file was deleted but the temporary one was not renamed due to some error - see your OS documentation for this.
Here's an idea:
#include <iostream>
#include <fstream>
#include <string>
#include <cstdio>
using namespace std;
void replace(string& s, const string& old_str, const string& new_str)
{
for (size_t off = 0, found_idx = s.find(old_str, off); found_idx != string::npos; off += new_str.length(), found_idx = s.find(old_str, off))
s.replace(found_idx, old_str.length(), new_str);
}
int main()
{
const char* in_fn = "c:/temp/in.txt";
const char* bak_fn = "c:/temp/in.bak";
const char* tmp_fn = "c:/temp/tmp.txt";
const char* out_fn = "c:/temp/out.txt";
string old_str{ "2002" };
string new_str{ "2003" };
// read, rename, write
{
ifstream in{ in_fn };
if (!in)
return -1; // could not open
ofstream tmp{ tmp_fn };
if (!tmp)
return -2; // could not open
string line;
while (getline(in, line))
{
replace(line, old_str, new_str);
tmp << line << endl;
}
} // in & tmp are closed here
// this should be done in one step
{
remove(bak_fn);
rename(in_fn, bak_fn);
remove(out_fn);
rename(tmp_fn, in_fn);
remove(tmp_fn);
}
return 0;
}
One possible way:
Close the file after you read it into "line" variable, then:
std::replace(0, line.length(), "2002", "2003")
Then overwrite the old file.
Note that std::replace is different from string::replace!!
The header is supposed to be <fstream> rather than <stream>
you can't read and write to a file simultaneously so I have closed the file after reading before reopening the file for writing.
instead of updating text inside the file, your line can be updated and then written to file.
#include <iostream>
#include <fstream>
#include <string.h>
#include <string>
using namespace std;
int main(){
string srch;
string line, line2;
fstream Myfile;
string word, replacement, name;
int counter;
Myfile.open("Patientlist.txt", ios::in);
cout << "\nEnter your Name: ";
cin.ignore();
getline(cin, srch);
if(Myfile.is_open())
{
while(getline(Myfile, line)){
if (line.find(srch) != string::npos){
cout << "\nYour details are: \n" << line << endl << "What do you want to change? *type it's word and then type the replacement!*" << endl;
cin >> word >> replacement;
int index = line.find(word);
if (index != string::npos){
Myfile.close();
Myfile.open("Patientlist.txt", ios::out);
line.replace(index, word.length(), replacement);
Myfile.write(line.data(), line.size());
Myfile.close();
}
}
// i want to change in here
}
}else
{
cout << "\nSearch Failed... Patient not found!" << endl;
}
}
I am trying to input three pieces of information from a .txt file.
First column is the course mark.
Second column is the course code.
Third column(s) is the course name.
I would like to store these as 3 vectors of strings.
Would using stringstream be a good option here? and maybe iterators?
The .txt file is like
65.6 10071 Mathematics 1
66.7 10101 Dynamics
60.0 10121 Quantum Physics and Relativity
66.9 10191 Introduction to Astrophysics and Cosmology
... ... ...
and my code so far is
#include<iostream>
#include<iomanip>
#include<fstream>
#include<cmath>
#include<algorithm>
#include<string>
#include<iterator>
#include<sstream>
#include<vector>
//Main Function
int main()
{
//Define variables
std::string course_mark, course_code, course_name;
std::vector<std::string> course_mark_vector;
std::vector<std::string> course_code_vector;
std::vector<std::string> course_name_vector;
std::string data_file[100];
// Ask user to enter filename
std::cout<<"Enter data filename: ";
std::cin>>data_file;
int i{0};
// Open file and check if successful
std::fstream course_stream(data_file);
if(course_stream.is_open()) {
while (!course_stream.eof()) //while the end of file is NOT reached
{
//I have 2
getline(course_stream, course_mark, ' ');
course_mark_vector.push_back(course_mark);
getline(course_stream, course_code, ' ');
course_code_vector.push_back(course_code);
getline(course_stream, course_name, '\n');
course_name_vector.push_back(course_name);
i += 1; //increment number of lines
}
course_stream.close(); //closing the file
std::cout << "Number of entries: " << i-1 << std::endl;
}
else{
std::cout << "Unable to open file. Please run again" << std::endl;
return 1;
}
Any help would be greatly appreciated
Would using stringstream be a good option here?
Yes.
and maybe iterators?
There is no need for iterators in this case.
Try this:
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
#include <iomanip>
//Main Function
int main()
{
//Define variables
std::string course_mark, course_code, course_name, data_file, line;
std::vector<std::string> course_mark_vector, course_code_vector, course_name_vector;
int i = 0;
// Ask user to enter filename
std::cout << "Enter data filename: ";
std::cin >> data_file;
// Open file and check if successful
std::ifstream course_stream(data_file);
if (!course_stream.is_open())
{
std::cout << "Unable to open file. Please run again" << std::endl;
return 1;
}
while (std::getline(course_stream, line)) //while the end of file is NOT reached
{
std::istringstream iss(line);
iss >> course_mark;
course_mark_vector.push_back(course_mark);
iss >> course_code;
course_code_vector.push_back(course_code);
std::getline(iss >> std::ws, course_name);
course_name_vector.push_back(course_name);
++i; //increment number of lines
}
course_stream.close(); //closing the file
std::cout << "Number of entries: " << i << std::endl;
return 0;
}
Demo
This is my first project in C++. I took a course using C previously and file I/O seems to differ a little.
The project requires the user to enter a name for saving the output file.
I know I should use ofstream which should look like this:
ofstream myfile;
myfile.open ("example.txt");
myfile << "Writing this to a file.\n";
myfile.close();
I've bolded the snippet that's causing confusion.
How can I name the file from a string entered by the user?
*Note, C type string, so an array of characters.
#include < string > is not allowed
As my other answer has got a negative vote, here's another solution without #include <string>
You can just save the input from the user in a temporary char array and then save it to a string variable std::string.
Includes that are necessary:
#include <iostream>
#include <fstream>
Saving an input from an user into a char array:
char input[260];
cin >> input;
To then save it in a string variable just do this:
string filename = input;
To open a file stream you'll need to use std::ofstream. Please keep in mind, that the file is created in the same folder as the project/application is.
std::ofstream outfile (filename + "." + "file extension");
And as you already know this outfile.open(); opens the file.
With outfile << "hello"; you can write into the file.
To close the file, use outfile.close(); to close the file.
Here you have a little example code:
#include <iostream>
#include <fstream>
using namespace std;
void main()
{
char input[260];
cin >> input;
string filename = input;
ofstream outfile(filename + "." + "txt");
outfile << "hello";
outfile.close();
}
I hope this helps.
Regards.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
string path;
string name;
string h_path;
string text;
void create() {
ofstream file(h_path, ios::app);
if (!file.fail()) {
file << text;
file.close();
}
}
int main() {
cout << "please enter path(c:\\folder\): ";
cin >> path;
cin.ignore();
path = path + "/";
cout << "please enter the name of the file (test.txt): ";
getline(cin, name);
cout << "content of the file: ";
getline(cin, text);
h_path = path + name;
create();
cout << "new file created";
cout << h_path;
}
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
int main()
{
string fileName;
cin >> fileName;
ofstream myfile;
myfile.open(fileName);
myfile << "Writing this to a file.\n";
myfile.close();
}
So Lets say this is what the input file contains
12
Hello
45
54
100
Cheese
23
How would I print it out on the screen in that order.
This is what I had but it skips some lines.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
int number;
string word;
int loop = 0;
ifstream infile;
infile.open("arraynumbers.txt");
while(infile >> number >> word)
{
if( infile >> number)
{
cout << number << endl;
}
if(infile >> word)
{
cout << word << endl;
}
}
return 0;
}
I suggest using www.cplusplus.com to answer these questions.
However, you are on the right track. Since you are just outputting the contents of the file to stdout, I suggest using readline() and a string. If you need to access the numeric strings as ints, use the atoi() function.
Example:
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
string line;
ifstream file("arraynumber.txt");
if (file.is_open()) {
while (getline(file, line)) {
cout << line << endl;
}
file.close();
} else cout << "Error opening arraynumber.txt: File not found in current directory\n";
return 0;
So I've been playing with code and I'm stuck with finding how to replace the line found. I'm able to find the name and add the 'new_gpa' to the section but it outputs the final result in the same file but without replacing the original score and name.
how could I remove the original line found along with the gpa? and also store the new values to the file.
cristian 2.1
rachel 3.0
name search: cristian
new file:
cristian 2.1
rachel 3.0
cristian 4.1
The code is below.
#include <iostream>
#include <string>
#include <sstream>
#include <algorithm>
#include <vector>
#include <fstream>
#include <sstream>
#include <cstring>
using namespace std;
int main()
{
string name;
int offset;
string line;
ifstream read_file;
read_file.open("alpha.dat", std::ios_base::app);
cout << "Please enter your name: \n";
cin>> name;
if (read_file.is_open())
{
while(!read_file.eof())
{
getline(read_file,line);
if((offset = line.find(name)) != string::npos)
{
cout <<"the word has been found: \n";
//cout << line //example to display
//new code
istringstream iss ( line );
string thisname;
double gpa;
double new_gpa = 2.1;
if( iss >> thisname >> gpa)
{
if (thisname == name)
{
cout << name <<endl;
cout << gpa <<endl;
ofstream myfile;
myfile.open("alpha.dat",std::ios_base::app);
myfile << " \n" << name << " " << gpa+ new_gpa;
myfile.close();
read_file.close();
}
}
}
}
}
return 0;
}
You open file with std::ios_base::app, which means all you output operations are performed at the end of file, appending the content to the current file. But what you want to do is modify the data at the original place. So you should open file with std::ios_base::in, and function seekp can help you in the next step.