I just need to write a string into a file created using ofstream, but I am getting an error.
This is the code:
#include <iostream>
#include <fstream>
using namespace std;
int main ()
{
QString aux = "Hello";
ofstream myfile ("test.txt");
if (myfile.is_open())
{
myfile << aux;
myfile.close();
}
else
{
cout << "CANT OPEN FILE";
}
return 0;
}
The error is: no match for 'operator<<' in 'myfile << aux'
P.S: I am using QT4
Thanks for your help!
You should convert to a string by doing :
myfile << aux.toStdString();
This is because the << operator does not know any conversion from qt string.
Related
I've tried to write to file in C++ on a mac in different ways and I can't.
I've used:
int bestScore = 3;
QFile data("bestScore.txt");
data.open(QIODevice::WriteOnly);
QTextStream out(&data);
out << bestScore;
data.close();
int bestScore = 3;
FILE *out_file = fopen("bestScore.txt", "w");
if (out_file == NULL)
{
qDebug() << "File not open";
}
fprintf(out_file, "%d", bestScore);
Can anyone help?
First thing you need to include fstream.
Second you declare the name of the file as an variable.
You need to open it.
#include <iostream>
#include <fstream>
using namespace std;
int main () {
ofstream myfile;
myfile.open ("example.txt");
myfile << "Writing this to a file.\n";
myfile.close();
return 0;
}
If this dosen't work try to give the exact location of the file example
myfile.open ("/Library/Application/randomfilename/example.txt");
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <string>
using namespace std;
int main() {
fstream a_file_that_will_be_working_with("storage.txt");
if (a_file_that_will_be_working_with.is_open()) {
cout << "is open";
}
else
{
cout << "is not open";
}
a_file_that_will_be_working_with << "first text" << endl;
a_file_that_will_be_working_with << "second text" << endl;
while (a_file_that_will_be_working_with)
{
// read stuff from the file into a string and print it
string strInput;
a_file_that_will_be_working_with >> strInput;
cout << strInput << '\n';
}
return 0;
}
What have I done wrong?
When I use ifstream to read from a file it works, but it doesnt for fstream, I thought fstream is both ofstream and ifstream combined.
See https://en.cppreference.com/w/cpp/io/basic_fstream for an example.
You need to "rewind" the file to read just written stuff (s.seekp(0);).
And thisI am trying to get the things written in a .txt file called CodeHere.txt and here is my main.cpp:
#include <iostream>
#include <fstream>
using namespace std;
int main(int argc, const char * argv[]) {
string line;
string lines[100];
ifstream myfile ("CodeHere.txt");
int i = 0;
if (myfile.is_open())
{
while ( getline (myfile,line) )
{
lines[0] = line;
i++;
}
myfile.close();
}
else cout << "Unable to open file";
cout << lines[0];
myfile.close();
return 0;
}
And the output is: Writing this to a file.Program ended with exit code: 0
But in my CodeHere.txt it has: hello
I tried saving it, but the result didn't change. I'm not sure whats going on. Can anyone help?
Are you sure that your .txt file is in the same repertory? To me, it just looks like you entered the path wrong. Try with the absolute path (full one). Another option is that you haven't saved the text file yet, you're just editing it, and so it is in fact empty, that would be why your cout doesn't print anything.
This should work, using a vector<string> to store the lines read from file
#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
int main(int argc, const char * argv[]) {
string line;
vector<string> lines;
ifstream myfile ("CodeHere.txt");
int i = 0;
if (myfile.is_open())
{
while ( getline(myfile, line) )
{
lines.push_back(line);
i++;
}
myfile.close();
}
else {
cout << "Unable to open file";
return -1;
}
cout << lines[0] << '\n';
return 0;
}
Try this:
vector<string> lines;
if (file.is_open()) {
// read all lines from the file
std::string line;
while (getline(file, line)) {
lines.emplace_back(line);
}
file.close();
}
else {
cout << "Unable to open file";
return -1;
}
cout << "file has " << lines.size() << " lines." << endl;
for (auto l : lines) {
cout << l << endl;
}
Premise: I'm using CLion.
As i said in title, when i try to open a file (txt) nothing will be displayed.
i can't explain it, i don't think i made an error, it's pretty easy this code:
#include <iostream>
#include <cstdlib>
using namespace std;
int main() {
FILE *leggi;
leggi = fopen("lorem.txt", "r");
char datiLetti[1000];
while(fgets(datiLetti, 1000, leggi)!=NULL){
cout << datiLetti << endl;
}
fclose(leggi);
system("PAUSE");
return EXIT_SUCCESS;
}
file "lorem.txt" is in the same directory of the project.
Thank you in advance.
EDIT1: file is lorem not lorem_ipsum, my mistake when i typed here.
You want this:
...
FILE *leggi;
leggi = fopen("lorem.txt", "r");
if (leggi == NULL)
{
cout << "Can't open file" << endl;
return 1;
}
...
---FIXED---
Installed cygwig1.dll and cygstdc++-6.dll and put cygwig in glob variables, then my file worked in the same directory of main and exe.
However, thank you guys for your time!
fopen is a C solution for open a file if you want to open a file in c++ use fstream like flowing code.
fopen is deprecated in c++11.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main() {
string line;
fstream myfile;
myfile.open("example.txt");
cerr << "Error: " << strerror(errno);
if (myfile.is_open())
{
while (getline(myfile, line))
{
cout << line << '\n';
}
myfile.close();
}
else cout << "Unable to open file";
return 0;
}
I'm trying to open a file using ifstream, but no matter what solutions I find that I've tried, nothing seems to work; my program always outputs "unable to open". Below is my code in its entirety. Any help at all is appreciated!
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main(int argc, char ** argv)
{
string junk;
ifstream fin;
fin.open("somefile.txt");
if(fin.is_open())
{
fin >> junk;
cout << junk;
}
else
{
cout << "unable to open" << endl;
}
fin.close();
return 0;
}
Also, the contents of somefile.txt, which is in the same directory as the created executable is the following:
SOME
FILE
As some commenters have suggested, it could easily be that the file truly doesn't exist, because you're looking for it in the wrong place. Try using an absolute path to the file rather than just assuming it's looking where you expect.
And output a more helpful error message using strerror(errno).
// ...
fin.open("C:\\path\\to\\somefile.txt");
// ...
else
{
cout << "unable to open: " << strerror(errno) << endl;
}