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;
}
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:
In Lua, I have such a function to read a file into an array:
function readFile(file)
local output = {}
local f = io.open(file)
for each in f:lines() do
output[#output+1] = each
end
f:close()
return output
end
Now in C++, I tried to write that like this:
string * readFile(file) {
string line;
static string output[] = {};
ifstream stream(file);
while(getline(stream, line)) {
output[sizeof(output)+1] = line;
}
stream.close();
return output;
}
I know you can't return arrays from functions, only pointers. So I did this:
string *lines = readFile("stuff.txt");
And it threw me the error cannot convert 'std::string {aka std::basic_string<char>} to' std::string* {aka std::basic_string<char>*}' in intialization string *lines = readFile("stuff.txt");
Can anyone tell me what is wrong here, and is there a better way to read files into arrays?
EDIT:
I'm going to be using the returned array to do value matching using a for loop. In Lua this would be written as:
for _, each in ipairs(output) do
if each == (some condition here) then
--Do Something
end
end
How can this be done in C++, using vectors (according to the answer by Jerry Coffin)?
EDIT 2:
I can't match the vectors correctly for some reason. I wrote the code in a separate test file.
int main() {
vector<string> stuff = read_pass();
cout << stuff.size() << endl;
cout << stuff[0] << endl;
if (stuff[0] == "admin") {
cout << "true";
}
else {
cout << "false";
}
return 0;
}
read_pass() looks like this:
vector<string> read_pass() {
ifstream stream("stuff.txt");
string line;
vector<string> lines;
while(getline(stream, line)) {
lines.push_back(line);
}
stream.close();
return lines;
}
And stuff.txt looks like this:
admin
why?
ksfndj
I just put it some random lines to test the code. Every time I compile and run main.cpp the output I get is
3
admin
false
So why isn't the code being matched properly?
EDIT 3:
So instead of forcing myself down the vectors method of doing things, I decided to try this instead:
#include <cstdlib>
#include <iostream>
#include <fstream>
#include <vector>
#include "basefunc.h"
using namespace std;
int main() {
string storedUsrnm;
string storedPw;
string pw = "admin";
string usrnm = "admin";
ifstream usernames("usrnm.accts");
ifstream passwords("usrpw.accts");
while(getline(usernames, storedUsrnm)) {
getline(passwords, storedPw);
print("StoredUsrnm " + storedUsrnm);
print("StoredPw: " + storedPw);
if (storedUsrnm == usrnm && storedPw == pw) {
print("True!");
return 0;
}
}
print("False!");
return 0;
}
Where print() is
void print(string str) {
cout << str << endl;
}
This still prints false, at the end, and it leads me to believe that for some reason, the "admin" read by the ifstream is different from the "admin" string. Any explanations for how this is so? Or does this code not work either?
Doesn't look to me like your current code should even compile. Anyway, I'd probably do something like this:
std::vector<std::string> read_file(std::istream &infile) {
std:string line;
std::vector<std::string> lines;
while (std::getline(infile, line))
lines.push_back(line);
return lines;
}
So the basic idea here is to read a line from the file, and if that succeeded, add that line (with push_back) to the vector of results. Repeat until reading a line from the file fails. Then return the vector of all the lines to the caller.
A few notes: especially at first, it's fairly safe to presume that any use of pointers is probably a mistake. That shouldn't be taken as an indication that pointers are terribly difficult to work with, or anything like that--just that they're almost never necessary for the kinds of things most relative beginners do in C++.
Likewise with arrays--at first, assume that what you might think of as an array in some other language translates to a std::vector in C++. C++ does also have arrays, but using them can wait a while (a long while, IMO--I've been writing C++ for decades now, and virtually never use raw pointers or arrays at all).
In the interest of simplicity, I've consolidated the data into the program, so it reads the data from the stringstream, like this:
#include <vector>
#include <string>
#include <fstream>
#include <iostream>
#include <sstream>
using namespace std;
vector<string> read_pass(istream &is) {
string line;
vector<string> lines;
while (getline(is, line)) {
lines.push_back(line);
}
return lines;
}
int main() {
istringstream input{ "admin\nwhy?\nksfndj" };
// To read from an external file, change the preceding line to:
// ifstream input{ "stuff.txt" };
vector<string> stuff = read_pass(input);
cout << stuff.size() << endl;
cout << stuff[0] << endl;
if (stuff[0] == "admin") {
cout << "true";
}
else {
cout << "false";
}
return 0;
}
At least for me, this produces:
3
admin
true
...indicating that it has worked as expected. I get the same with an external file. If you're not getting the same with an external file, my immediate guess would be that (at least the first line of) the file contains some data you're not expecting. If the problem continues, you might consider writing out the individual characters of the strings you read in numeric format, to give a more explicit idea of what you're really reading.
After a long time, I finally came up with the answer
#include <fstream>
#include <iostream>
#include <cstdlib>
#include <map>
using namespace std;
typedef map<int, string> strArr;
strArr readFile(string file) {
ifstream stream(file);
string line;
strArr output;
while(getline(stream, line)) {
output[output.size()+1] = line;
}
stream.close();
return output;
}
It doesn't read the file into an array, but it does return a map that does basically the same thing
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;
}
I'm in a tutorial which introduces files (how to read from file and write to file)
First of all, this is not a homework, this is just general help I'm seeking.
I know how to read one word at a time, but I don't know how to read one line at a time, or how to read the whole text file.
What if my file contains 1000 words? It is not practical to read entire file word after word.
My text file named "Read" contains the following:
I love to play games
I love reading
I have 2 books
This is what I have accomplished so far:
#include <iostream>
#include <fstream>
using namespace std;
int main (){
ifstream inFile;
inFile.open("Read.txt");
inFile >>
Is there any possible way to read the whole file at once, instead of reading each line or each word separately?
You can use std::getline :
#include <fstream>
#include <string>
int main()
{
std::ifstream file("Read.txt");
std::string str;
while (std::getline(file, str))
{
// Process str
}
}
Also note that it's better you just construct the file stream with the file names in it's constructor rather than explicitly opening (same goes for closing, just let the destructor do the work).
Further documentation about std::string::getline() can be read at CPP Reference.
Probably the easiest way to read a whole text file is just to concatenate those retrieved lines.
std::ifstream file("Read.txt");
std::string str;
std::string file_contents;
while (std::getline(file, str))
{
file_contents += str;
file_contents.push_back('\n');
}
I know this is a really really old thread but I'd like to also point out another way which is actually really simple... This is some sample code:
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main() {
ifstream file("filename.txt");
string content;
while(file >> content) {
cout << content << ' ';
}
return 0;
}
I think you could use istream .read() function. You can just loop with reasonable chunk size and read directly to memory buffer, then append it to some sort of arbitrary memory container (such as std::vector). I could write an example, but I doubt you want a complete solution; please let me know if you shall need any additional information.
Well, to do this one can also use the freopen function provided in C++ - http://www.cplusplus.com/reference/cstdio/freopen/ and read the file line by line as follows -:
#include<cstdio>
#include<iostream>
using namespace std;
int main(){
freopen("path to file", "rb", stdin);
string line;
while(getline(cin, line))
cout << line << endl;
return 0;
}
The above solutions are great, but there is a better solution to "read a file at once":
fstream f(filename);
stringstream iss;
iss << f.rdbuf();
string entireFile = iss.str();
you can also use this to read all the lines in the file one by one then print i
#include <iostream>
#include <fstream>
using namespace std;
bool check_file_is_empty ( ifstream& file){
return file.peek() == EOF ;
}
int main (){
string text[256];
int lineno ;
ifstream file("text.txt");
int num = 0;
while (!check_file_is_empty(file))
{
getline(file , text[num]);
num++;
}
for (int i = 0; i < num ; i++)
{
cout << "\nthis is the text in " << "line " << i+1 << " :: " << text[i] << endl ;
}
system("pause");
return 0;
}
hope this could help you :)
hello bro this is a way to read the string in the exact line using this code
hope this could help you !
#include <iostream>
#include <fstream>
using namespace std;
int main (){
string text[1];
int lineno ;
ifstream file("text.txt");
cout << "tell me which line of the file you want : " ;
cin >> lineno ;
for (int i = 0; i < lineno ; i++)
{
getline(file , text[0]);
}
cout << "\nthis is the text in which line you want befor :: " << text[0] << endl ;
system("pause");
return 0;
}
Good luck !
Another method that has not been mentioned yet is std::vector.
std::vector<std::string> line;
while(file >> mystr)
{
line.push_back(mystr);
}
Then you can simply iterate over the vector and modify/extract what you need/
The below snippet will help you to read files which consists of unicode characters
CString plainText="";
errno_t errCode = _tfopen_s(&fStream, FileLoc, _T("r, ccs=UNICODE"));
if (0 == errCode)
{
CStdioFile File(fStream);
CString Line;
while (File.ReadString(Line))
{
plainText += Line;
}
}
fflush(fStream);
fclose(fStream);
you should always close the file pointer after you read, otherwise it will leads to error