Here is my requirement: "I need to show to the user on a Console window, the output of a .txt file which will be modified continuously by a Third party application"
I have this code from cplusplus.com:
// reading a text file
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main () {
string line;
ifstream myfile ("test_results.txt");
if (myfile.is_open())
{
while ( myfile.good() )
{
getline (myfile,line);
cout << line << endl;
}
myfile.close();
}
else cout << "Unable to open file";
return 0;
}
Do I need any sort of time counter to read that file at certain regular intervals of time? Guide me, thanks in advance...
There are two approaches.
Platform-dependent
Use API, like inotify in Linux
Platform-independent
Query fs about file modifications, for example using boost::filesystem
http://www.boost.org/doc/libs/1_52_0/libs/filesystem/doc/reference.html#last_write_time
Related
I have a txt file, named mytext.txt, from which I want to read and save every line in C++. When I run the binary, I do ./file <mytext.txt
I'd like to do something
std::string line;
while(std::getline(std::cin,line)){
//here I want to save each line I scan}
but I have no clue on how to do that.
You can use a std::vector<string> to save the lines as so:
///your includes here
#include <vector>
std::vector<std::string> lines;
std::string line;
while(std::getline(std::cin,line))
lines.push_back(line);
You can look at the following documentation and example:
http://www.cplusplus.com/doc/tutorial/files/
Edit upon recommendation:
In the provided link below they explain how to open and close a text file, read lines and write lines and several other functionalities. For completeness of this answer an example will be given below:
// writing on a text file
#include <iostream>
#include <fstream>
using namespace std;
int main () {
ofstream myfile ("example.txt");
if (myfile.is_open())
{
myfile << "This is a line.\n";
myfile << "This is another line.\n";
myfile.close();
}
else cout << "Unable to open file";
return 0;
}
The above script will write the 2 lines into the text file named example.txt.
You can then read these lines with a somewhat similar script:
// reading a text file
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main () {
string line;
ifstream myfile ("example.txt");
if (myfile.is_open())
{
while ( getline (myfile,line) )
{
cout << line << '\n';
}
myfile.close();
}
else cout << "Unable to open file";
return 0;
}
Best regards
Ruud
Im new to c++ and i was trying to open a ".txt" file using ifstream. the file im using is called "ola.txt" which literally just contains two lines of text without punctuation just plain and simple text. The code that i wrote is this
#include <iostream>
#include <vector>
#include <fstream>
#include <iomanip>
#include <string>
using namespace std;
int main()
{
int x;
string line;
vector<int> vect;
ifstream inFile("C:\\Users\\ruial\\Desktop\\ola.txt");
inFile.open("C:\\Users\\ruial\\Desktop\\ola.txt");
if (inFile.is_open()) {
while (getline(inFile, line))
{
cout << line << '\n';
}
inFile.close();
}
else {
cout << "Unable to open file";
exit(1); // terminate with error
}
return 0;
}
The path to the file that i wrote is correct such that the file opens, but when the program runs it doesn´t cout the lines that i wrote on the txt file to the cmd, i dont know if this is somewhat important but im coding in visual studio 2019.
I can't seem to find the answer to this problem anywhere in the internet and to be honest i think im doing it right, any help would be much appreciated,thanks in advance.
You are trying to open the inFile twice. First time during inFile construction, ifstream inFile("C:\\Users\\ruial\\Desktop\\ola.txt"), second time you try to open it again with inFile.open("C:\\Users\\ruial\\Desktop\\ola.txt"), when it's already open, which is erroneous, and flags the stream as no longer good.
3 possible fixes:
Remove inFile.open("C:\\Users\\ruial\\Desktop\\ola.txt")
Use default constructor, without specifying the file name
inFile.close() before you open it again (obviously, not the nicest fix).
I currently have this code, but I would like to be able to output to a .csv file, rather than just print to screen. Does anyone know how to do this?
#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
string Weather_test;
int main()
{
ifstream Weather_test_input;
Weather_test_input.open("/Users/MyName/Desktop/Weather_test.csv");
getline(Weather_test_input, Weather_test, '?');
Weather_test.erase(remove_if(Weather_test.begin(), Weather_test.end(), ::isalpha), Weather_test.end());
cout << Weather_test;
return 0;
}
If the Weather_test string is formatted properly.
ofstream Weather_test_output("path_goes_here.csv", ios::app);
// this does the open for you, appending data to an existing file
Weather_test_output << Weather_test << std::endl;
Weather_test_output.close();
If it is not formatted properly then you need to separate it into "fields" and write them with commas between them. That's a separate question.
Writing a string to a CSV file is like writing a string to any file:
std::string text = "description"
output_file << description << ", " << 5 << "\n";
In your example, you can't write to an ifstream. You can write to ofstream and fstream but not ifstream.
So either open the file for reading and writing or close after reading and open as writing.
To write to csv is to create an ostream and open file named "*.csv". You can use operator<< on this object in the same way as you have used it previously to write to the standard output, std::cout:
std::ofstream f;
f.open( "file.csv", std::ios::out);
if ( !f) return -1;
f << Weather_test;
f.close();
Thanks people you here are all truly amazing!
I managed to get my final piece of code which (removes all letters of the alphabet from my .csv file). Here it is for posterity
#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
string Weather_test;
int main()
{
ifstream Weather_test_input;
Weather_test_input.open("/Users/MyName/Desktop/Weather_test.csv");
getline(Weather_test_input, Weather_test, '?');
Weather_test.erase(remove_if(Weather_test.begin(), Weather_test.end(), ::isalpha), Weather_test.end());
ofstream Weather_test_output("/Users/MyName/Desktop/Weather_test_output.csv", ios::app);
Weather_test_output << Weather_test << std::endl;
Weather_test_output.close();
cout << Weather_test;
return 0;
}
Thanks again all!
When I debug this I can see it opens datafile1 , it reads the firstline and
in the logfile I get roma-3-4.log
It change to c:/temp/roma-3-4.log but when I want to open it , it fails. I have check that the _Mystate = 2 .
What is the meaning of that
Thanks
in the transfersubs.cfg there is this
roma-3-4.log
** In the directory c:/temp/ I have the following file
roma-3-4.log
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
int main()
{
string input;
string logfile;
string errorfile;
short logfilesize1;
fstream dataFile1("c:/temp/transfersubs.cfg", ios::in);
if (dataFile1)
{
getline(dataFile1, input, '$');
logfile=input;
logfilesize1=input.size();
errorfile=input;
errorfile[logfilesize1-4]='e';
errorfile[logfilesize1-3]='r';
errorfile[logfilesize1-2]='r';
logfile="C:/Temp/"+logfile;
fstream dataFile2( logfile, ios::in);
if (dataFile2)
{
dataFile2.close();
}
else
{
cout << "ERROR: Cannot open logfile.\n";
}
dataFile1.close();
}
else
{
cout << "ERROR: Cannot open file.\n";
}
system("Pause");
return 0;
}
I believe your getline doesn't bother looking the newline but only for a $. You didn't post the file you are reading from, but check to ensure it has a $ at the end of the file name otherwise it will fetch the entire file.
It appears that unless you put a \n or endl after writing to the file using ofstream, ifstream won't be able to read anything from the file. In fact, adding a space after whatever you've written into file won't help either.
So always add a newline right after whatever it is that you've written to file using ofstream.
I'm trying to solve Problem 13 of project euler, which involves the sum of 100 50 digit numbers. I figured there would be a better way than the paste that whole chunk of numbers into my code. So I searched around and found that you could paste the chunk into a .txt file and read it from there.
So, how would I go about reading from a .txt file in C++ and more importantly getting the 50 digit strings individually from it?
Something like this?
// reading a text file
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main () {
string line;
ifstream myfile ("numbers.txt");
if (myfile.is_open())
{
while ( myfile.good() )
{
getline (myfile,line);
int i = atoi(line.c_str());
// do here something with 'i'
cout << i
}
myfile.close();
}
else cout << "Unable to open file";
return 0;
}