I want 41 output files to use in my project to write text on them. first create a string array list to name those output files then I tried to define an array of ofstream objects and use list to name them, but I get this error that 'outfile' cannot be used as a function. Below is my code:
#include <sstream>
#include <string>
#include <iostream>
#include <fstream>
using namespace std ;
int main ()
{
string list [41];
int i=1;
ofstream *outFile = new ofstream [41];
for (i=1;i<=41 ;i++)
{
stringstream sstm;
sstm << "subnode" << i;
list[i] = sstm.str();
}
for (i=0;i<=41;i++)
outFile[i] (list[i].c_str());
i=1;
for (i=1;i<=41;i++)
cout << list[i] << endl;
return 0;
}
See below for the following fixes:
don't use new unless you have to (you were leaking all files and not properly destructing them will lead to lost data; ofstreams might not be flushed if you don't close them properly, and the pending output buffer will be lost)
Use proper array indexing (starting from 0!)
Call .open(...) on a default-constructed ofstream to open a file
Recommendations:
I'd recommend against using namespace std; (not changed below)
I recommend reusing the stringstream. This is is good practice
Prefer to use C++-style loop index variables (for (int i = ....). This prevents surprises from i having excess scope.
In fact, get with the times and use ranged for
#include <sstream>
#include <string>
#include <iostream>
#include <fstream>
using namespace std;
int main ()
{
ofstream outFile[41];
stringstream sstm;
for (int i=0;i<41 ;i++)
{
sstm.str("");
sstm << "subnode" << i;
outFile[i].open(sstm.str());
}
for (auto& o:outFile)
cout << std::boolalpha << o.good() << endl;
}
You can not call the constructor as you do. Try calling outFile[i].open(list[i].c_str()). Note the 'open'.
Related
I need help, I wrote the code, did the reverse thing but I can't get it written on another file.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
ifstream par2("C:/fajllat/f1.bin", ios::in);
string line;
for (int i = 1; !par2.eof() ; i++)
{
getline(par2, line);
if (i < 5 || i >14) continue;
line = string(line.rbegin(), line.rend());
}
par2.close();
ofstream mbrapsht ("C:/fajllat/f3.bin", ios::out);
mbrapsht << line;
mbrapsht.close();
cin.get();cin.get();
return 0;
}
When I check the files the f3.bin file is empty
You have the right idea. What you're missing is that if you want to write the reversed lines, you need to either write them inside the loop or store them for after. You are doing neither of these things.
Currently what happens is you overwrite line every loop. And whatever is left in that string is what you write afterwards. Turns out that for your case, that's an empty string.
Let's make minimal changes to what you have:
// (*) Open the output file before looping
ofstream mbrapsht("C:/fajllat/f3.bin", ios::out);
for (int i = 1; !par2.eof() ; i++)
{
getline(par2, line);
if (i < 5 || i > 14) continue;
line = string(line.rbegin(), line.rend());
// (*) output the line - you also probably want an end-of-line
mbrapsht << line << std::endl;
}
Now, it's okay-ish. But it does have a problem where if getline fails, your code still runs the loop body one more time. This happens if getline hits the end of file (or some other error state), which your loop doesn't pick up until the next iteration (or possibly never, if the error is not EOF).
So, a somewhat better choice might be:
for(int lineNo = 1; std::getline(par2, line); ++lineNo)
{
if (lineNo >= 5 && lineNo <= 14)
{
std::reverse(line.begin(), line.end()); // (*) requires <algorithm>
mbrapsht << line << std::endl;
}
}
Note that I also inverted your test condition and removed the continue. In general, I avoid continue and break in loops unless not using them results in code that is hard to follow or understand at a glance. It's a style/maintainability thing. Take it or leave it.
See this snippet . For line-by-line reversal, you can use getline() instead and reverse before pushing into vector<string>.
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include <algorithm>
using namespace std;
int main()
{
string str;
ifstream par2("D:\\MyFolder\\try.txt", ios::in);
if (par2.is_open())
{
stringstream strStream;
strStream << par2.rdbuf();
str = strStream.str();
cout << str << endl;
par2.close();
}
cout << "\n\nReversing ...\n\n";
std::reverse(str.begin(), str.end());
cout << str << endl;
ofstream mbrapsht("D:\\MyFolder\\try2.txt", ios::out);
mbrapsht << str;
mbrapsht.close();
return 0;
}
Output:
Here is what I got so far:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
int characterList = 0;
char* dynamo = new char[1000];
char* buffer = dynamo;
ifstream input("wordlist.txt");
if (input.is_open())
{
input >> dynamo[characterList];
while (input.eof())
{
characterList++;
input >> dynamo[characterList];
cout << dynamo[characterList];
}
}
else
{
cout << "File not opened" << endl;
}
return;
}
I'm a beginner so I do apologize if this looks like terrible coding practice. I created a text file with a quote from Bill Cosby that I'm trying to read one word at a time. The quote is "I don't know the key to success, but the key to failure is trying to please everybody." I'm trying to read one word at a time from a text document ignoring punctuation. I know there are a lot of questions similar to this, but they are using code that I have not learned so I'm sorry for having a repeating question. I have not learned getline (I used cin.getline) and #include <string>.
Edit: I forgot to mention, so I'm sorry for not doing so earlier, but I'm studying dynamic memory allocation which is why I'm using the new char[1000].
I'd suggest you to use std::string instead of manually allocating buffers on the heap with new[] and trying to read text manually from the file into those buffers (and don't forget to free the buffer with proper delete[] calls!).
C++ input stream classes like std::ifstream can simply read text into std::string instances thanks to a proper overload of operator<<.
The syntax is as simple as:
string word;
while (inFile >> word)
{
cout << word << endl;
}
Here's a complete compilable sample code for you to experiment and learn:
#include <fstream>
#include <iostream>
#include <string>
using namespace std;
int main()
{
ifstream inFile("test.txt");
if (inFile.is_open())
{
string word;
while (inFile >> word)
{
cout << word << endl;
}
}
else
{
cout << "Can't open file." << endl;
}
}
This is the output I got on a test text file having the content specified in your question:
I
don't
know
the
key
to
success,
but
the
key
to
failure
is
trying
to
please
everybody.
NOTE
Of course, once you have your words read into a std::string instance, you can store them in a container like std::vector<std::string>, using its push_back() method.
I would do something like this:
#include <iostream>
#include <string>
#include <fstream>
int main() {
std::string array[6];
std::ifstream infile("Team.txt");
std::string line;
int i = 0;
while (std::getline(infile, line)) {
array[i++] = line;
}
return 0;
}
based on this answer.
Here, we assume we have to read 6 lines from the file "Team.txt". We use std:::getline() and we put inside a while so that we read all the file.
At every iteration, line holds the current line of the file read. Inside the body we store it in array[i].
I am trying to write a C++ program, but I am not familiar with C++. I have a .txt file, which contains values as follows:
0
0.0146484
0.0292969
0.0439453
0.0585938
0.0732422
0.0878906
What I have done in my C++ code is as follows:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
string line;
ifstream myReadFile;
myReadFile.open("Qi.txt");
if(myReadFile.is_open())
{
while(myReadFile.good())
{
getline(myReadFile,line);
cout << line << endl;
}
myReadFile.close();
}
return 0;
}
I would like to make the output of the program an array, i.e.
line[0] = 0
line[1] = 0.0146484
line[2] = 0.0292969
line[3] = 0.0439453
line[4] = 0.0585938
line[5] = 0.0732422
line[6] = 0.0878906
Assuming you want your data stored as floating point numbers (not strings) you probably want to do something like this:
#include <iostream>
#include <vector>
#include <iterator>
#include <fstream>
int main() {
std::ifstream in("Qi.txt");
// initialize the vector from the values in the file:
std::vector<double> lines{ std::istream_iterator<double>(in),
std::istream_iterator<double>() };
// Display the values:
for (int i=0; i<lines.size(); i++)
std::cout << "lines[" << i << "] = " << lines[i] << '\n';
}
Just a quick note on style: I prefer to see variables fully initialized right when you create them, so std::ifstream in("Qi.txt"); is preferable to std::ifstream in; in.open("Qi.txt");. Likewise, it's preferable to initialize the vector of lines directly from istream iterators rather than create an empty vector, then fill it in an explicit loop.
Finally, note that if you insist on writing an explicit loop anyway, you never want to use something like while (somestream.good()) or while (!somestream.eof()) to control your loop -- these are mostly broken, so they don't (dependably) read a file correctly. Depending on the type of data involved, they'll frequently appear to read the last item from the file twice. Usually, you want something like while (file >> value) or while (std::getline(file, somestring)). These check the state of the file immediately after reading, so as soon as reading fails they fall out of the loop, avoiding the problems of the while (good()) style.
Oh, as a side note: this is written expecting a compiler that (at lest sort of) conforms with C++11. For an older compiler you'd want to change this:
// initialize the vector from the values in the file:
std::vector<double> lines{ std::istream_iterator<double>(in),
std::istream_iterator<double>() };
...to something like this:
// initialize the vector from the values in the file:
std::vector<double> lines(( std::istream_iterator<double>(in)),
std::istream_iterator<double>() );
First you'll need a vector:
std::vector<std::string> lines; // requires #include <vector>
Then you'll need to take a string taken from the getline operation, and push it back into the vector. It's very simple:
for (std::string line; std::getline(myReadFile, line);)
{
lines.push_back(line);
}
For an output operation, all you need is:
{
int i = 0;
for (auto a : lines)
{
std::cout << "lines[" << i++ << "] = " << a << std::endl;
}
}
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
string line;
ifstream myReadFile;
myReadFile.open("Qi.txt");
if(myReadFile.is_open())
{
for(int i=0;i<7;++i)
if(myReadFile.good())
{
getline(myReadFile,line);
cout<<"line["<<i<<"] = " << line << endl;
}
myReadFile.close();
}
return 0;
}
A novice at C++, i am trying to create a stats program to practice coding. i am hoping to get a text file, read it and store values into arrays on which i can perform mathematical operations. i am stuck here
main ()
{
char output[100];
char *charptr;
int age[100];
ifstream inFile;
inFile.open("data.txt");
if(!inFile)
{
cout<<"didn't work";
cin.get();
exit (1);
}
inFile.getline(output,100);
charptr = strtok(output," ");
for (int x=0;x<105;x++)
{
age[x] = atoi(charptr);
cout<<*age<<endl;
}
cin.get();
}
in the code above, I am trying to store subject ages into the int array 'age', keeping ages in the first line of the file. I intend to use strtok as mentioned, but i am unable to convert the tokens into the array.
As you can obviously see, I am a complete noob please bear with me as I am learning this on my own. :)
Thanks
P.S: I have read similar threads but am unable to follow the detailed code given there.
There are a few issues with the for loop:
Possibility of going out-of-bounds due to age having 100 elements, but terminating condition in for loop is x < 105
No check on charptr being NULL prior to use
No subsequent call to strtok() inside for loop
Printing of age elements is incorrect
The following would be example fix of the for loop:
charptr = strtok(output, " ");
int x = 0;
while (charptr && x < sizeof(age)/sizeof(age[0]))
{
age[x] = atoi(charptr);
cout << age[x] << endl;
charptr = strtok(NULL, " ");
x++;
}
As this is C++, suggest:
using std::vector<int> instead of a fixed size array
use the std::getline() to avoid specifying a fixed size buffer for reading a line
use std::copy() with istream_iterator for parsing the line of integers
For example:
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
#include <algorithm>
#include <iterator>
int main ()
{
std::vector<int> ages;
std::ifstream inFile;
inFile.open("data.txt");
if(!inFile)
{
std::cout<<"didn't work";
std::cin.get();
exit (1);
}
std::string line;
std::getline(inFile, line);
std::istringstream in(line);
std::copy(std::istream_iterator<int>(in),
std::istream_iterator<int>(),
std::back_inserter(ages));
return 0;
}
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
int main() {
char x[20];
cout << "enter something\n";
cin.getline(x,20);
ofstream o("d:/tester.txt");
//o.write( (char*)&x , sizeof(x) );
for(int i = 0 ; i<=19 ; i++ ) {
o.put(x[i]);
}
}
I am not getting that output in the file the one which i enter during program . for eg. the output is 畳慨汩朠灵慴찀쳌쳌쳌 on writing suhail gupta.
What is the problem with the code ? Even when i use o.write( (char*)&x , sizeof(x) ); (the commented statement) i get the same output.
What is the reason?
Your program involves undefined behavior. The x array is not fully initialized and you read from the uninitialized indices. Besides, you always write 20 bytes, independent of what you read from the user.
I guess you use some text editor like Notepad. The latter has bugs when trying to guess the encoding. It appears that it guesses the file is UTF16 and displays 20/2 == 10 characters instead.
To solve the problem, store to the file exactly the number of characters entered by the user. Use std::string to make it easier.
Edit: The C++ way:
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
int main() {
string x;
cout << "enter something\n";
getline(cin, x);
ofstream o("d:/tester.txt");
o << x;
}