I've the need of read a txt file that is structured in this way
0,2,P,B
1,3,K,W
4,6,N,B
etc.
Now I need to read in an array like arr[X][4]
The problem is that I don't know the number of lines inside this file.
In addition I'd need 2 integers and 2 char from it...
I think I can read it with this sample of code
ifstream f("file.txt");
while(f.good()) {
getline(f, bu[a], ',');
}
obviusly this only shows you what I think I can use....but I'm open to any advice
thx in advance and sry for my eng
Define a simple struct to represent a single line in the file and use a vector of those structs. Using a vector avoids having to manage dynamic allocation explicitly and will grow as required.
For example:
struct my_line
{
int first_number;
int second_number;
char first_char;
char second_char;
// Default copy constructor and assignment operator
// are correct.
};
std::vector<my_line> lines_from_file;
Read the lines in full and then split them as the posted code would allow 5 comma separated fields on a line for example, when only 4 is expected:
std::string line;
while (std::getline(f, line))
{
// Process 'line' and construct a new 'my_line' instance
// if 'line' was in a valid format.
struct my_line current_line;
// There are several options for reading formatted text:
// - std::sscanf()
// - boost::split()
// - istringstream
//
if (4 == std::sscanf(line.c_str(),
"%d,%d,%c,%c",
¤t_line.first_number,
¤t_line.second_number,
¤t_line.first_char,
¤t_line.second_char))
{
// Append.
lines_from_file.push_back(current_line);
}
}
Related
I am new to C++ and I am reading in a text file. The content of text file is like:
$ (first line)
2 (second)
MY NAME IS (whatever sentence with 10 or below characters)(third)
12 21 (forth)
22 22 (fifth)
221 (sixth)
fly jump run (seventh)
fish animal (eighth)
So I need to read all of these and store them into different variables line by line and so far I'd manage to store them into string array line by line but how can I store the numbers like 12 21 in forth line into 2 different integer variables such as int b and int c?
and also like last two line
how can I store the fly jump run fish animal into 5 different string variables respectively?
Basically Now I am putting them into a string array line by line and trying to access them and take them out of the array and store it.
if (file.is_open()){
cout<<"Congratulations! Your file was successfully read!";
while (!file.eof()){
getline(file,line);
txt[i]=line;
i++;
}
}
Just want to store every line into variables based on their data type.
The streams support streaming the content directly into the basic data types (int, double etc.). So the istream::operator>>(int&) does the work for you.
The below small sample class demonstrates it by reading your sample file into the members -- hope that helps:
class Creature
{
public:
void read(istream& stream)
{
string line;
stream.ignore(10, '\n'); // skip line 1 (= $)
stream >> m_integers[0]; // line 2 = single int
stream.ignore(1, '\n'); // skip end of line
getline(stream, m_sentence); // get the full sentence line ..
// and the rest ... we can read that in a single code line ...
stream >> m_integers[1] >> m_integers[2] >> m_integers[3] >> m_integers[4]
>> m_integers[5] >> m_whatCanIdDo[0] >> m_whatCanIdDo[1] >> m_whatCanIdDo[2] >> m_whatIAm[0] >> m_whatIAm[1];
}
private:
string m_sentence;
int m_integers[6];
string m_whatCanIdDo[3];
string m_whatIAm[2];
};
Calling the function:
int main()
{
ifstream file;
file.open("creature.txt");
Creature cr;
cr.read(file);
file.close();
}
There are several ways of doing this, but one of the most straightforward is to use a stringstream.
To do this, copy the lines you want to tokenize from your txt array into a stringstream. Use the stream extratction operator (>>) to read out each word from that line, separated by a space, into a separate variable.
//Required headers
#include <string>
#include <sstream>
...
string word1, word2;
stringstream words(txt[lineNumber]);
words >> word1 >> word2;
//Process words
For each line you tokenize, you'll have to reset the stream.
//Read in next line
lineNumber++;
//Reset stream flags
words.clear();
//Replace the stream's input string
words.str(txt[lineNumber]);
words >> word1 >> word2;
//Process new words
You can use the same process for both integers and strings. The stream extraction operator will automatically convert strings to whatever data type you give it. However, it's up to you to make sure that the data it's trying to convert is the correct type. If you try to write a string to an int using a stringstream, the stringstream will set a fail bit and you won't get any useful output.
It's a good idea to write your input to a string, and then check whether that string is, in fact, a number, before trying to write it to an integer. But that's an entirely different topic, there are many ways to do it, and there are several other questions on this site that cover it.
This question already has answers here:
Why does reading a record struct fields from std::istream fail, and how can I fix it?
(9 answers)
Closed 6 years ago.
I was wondering how to store data from a CSV file into a structured array. I realize I need to use getline and such and so far I have come up with this code:
This is my struct:
struct csvData //creating a structure
{
string username; //creating a vector of strings called username
float gpa; //creating a vector of floats called gpa
int age; //creating a vector of ints called age
};
This is my data reader and the part that stores the data:
csvData arrayData[10];
string data;
ifstream infile; //creating object with ifstream
infile.open("datafile.csv"); //opening file
if (infile.is_open()) //error check
int i=0;
while(getline(infile, data));
{
stringstream ss(data);
ss >> arrayData[i].username;
ss >> arrayData[i].gpa;
ss >> arrayData[i].age;
i++;
}
Further, this is how I was attempting to print out the information:
for (int z = 0; z<10; z++)
{
cout<<arrayData[z].username<<arrayData[z].gpa<<arrayData[z].age<<endl;
}
However, when running this command, I get a cout of what seem to be random numbers:
1.83751e-0383 03 4.2039e-0453 1.8368e-0383 07011688
I assume this has to be the array running not storing the variables correctly and thus I am reading out random memory slots, however, I am unsure.
Lastly, here is the CSV file I am attempting to read.
username,gpa,age
Steven,3.2,20
Will,3.4,19
Ryan,3.6,19
Tom,3,19
There's nothing in your parsing code that actually attempts to parse the single line into the individual fields:
while(getline(infile, data));
{
This correctly reads a single line from the input file into the data string.
stringstream ss(data);
ss >> arrayData[i].username;
ss >> arrayData[i].gpa;
ss >> arrayData[i].age;
You need to try to explain to your rubber duck how this is supposed to take a single line of comma-separated values, like the one you showed in your question:
Steven,3.2,20
and separate that string into the individual values, by commas. There's nothing about the >> operator that will do this. operator>> separates input using whitespaces, not commas. Your suspicions were correct, you were not parsing the input correctly.
This is a task that you have to do yourself. I am presuming that you would like, as a learning experience, or as a homework assignment, to do this yourself, manually. Well, then, do it yourself. You have the a single line in data. Use any number of tools that C++ gives you: the std::string's find() method, or std::find() from <algorithm>, to find each comma in the data string, then extract each individual portion of the string that's between each comma. Then, you still need to convert the two numeric fields into the appropriate datatypes. And that's when you put each one of them into a std::istringstream, and use operator>> to convert them to numeric types.
But, having said all that, there's an alternative dirty trick, to solve this problem quickly. Recall that the original line in data contains
Steven,3.2,20
All you have to do is replace the commas with spaces, turning it into:
Steven 3.2 20
Replacing commas with spaces is trivial with std::replace(), or with a small loop. Then, you can stuff the result into a std::istringstream, and use operator>> to extract the individual whitespace-delimited values into the discrete variables, using the code that you've already written.
Just a small word of warning: if this was indeed your homework assignment, to write code to manually parse and extract comma-delimited values, it's not guaranteed that your instructor will give you the full grade for taking the dirty-trick approach...
UNDER CONSTRUCTION
Ton, nice try and nice complete question. Here is the answer:
1) You have a semicolon after the loop:
while(getline(infile, data));
delete it.
How did I figure that out easily? I compiled with all the warnings enabled, like this:
C02QT2UBFVH6-lm:~ gsamaras$ g++ -Wall main.cpp
main.cpp:24:33: warning: while loop has empty body [-Wempty-body]
while(getline(infile, data));
^
main.cpp:24:33: note: put the semicolon on a separate line to silence this warning
1 warning generated.
In fact, you should get that warning without -Wall as well, but get into using it, it will also make good to you! :)
2) Then, you read some elements, but not 10, so why do you print 10? Print as many as the ones you actually read, i.e. i.
When you try to print all 10 elements of your array, you print elements that are not initialized, since you didn't initialize your array of structs.
Moreover, the number of lines in datafile.csv was less than 10. So you started populating your array, but you stopped, when the file didn't have more lines. As a result, some of the elements of your array (the last 6 elements) remained uninitialized.
Printing uninitialized data, causes Undefined Behavior, that's why you see garbage values.
3) Also this:
if (infile.is_open()) //error check
could be written like this:
if (!infile.is_open())
cerr << "Error Message by Mr. Tom\n";
Putting them all together:
WILL STILL NOT WORK, BECAUSE ss >> arrayData[i].username; eats the entire input line and the next two extractions fail, as Pete Becker said, but I leave it here, so that others won't make the same attempt!!!!!!!
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
using namespace std;
struct csvData //creating a structure
{
string username; //creating a vector of strings called username
float gpa; //creating a vector of floats called gpa
int age; //creating a vector of ints called age
};
int main()
{
csvData arrayData[10];
string data;
ifstream infile; //creating object with ifstream
infile.open("datafile.csv"); //opening file
if (!infile.is_open()) { cerr << "File is not opened..\n"; }
int i=0;
while(getline(infile, data))
{
stringstream ss(data);
ss >> arrayData[i].username;
ss >> arrayData[i].gpa;
ss >> arrayData[i].age;
i++;
}
for (int z = 0; z< i; z++)
{
cout<<arrayData[z].username<<arrayData[z].gpa<<arrayData[z].age<<endl;
}
return 0;
}
Output:
C02QT2UBFVH6-lm:~ gsamaras$ g++ -Wall main.cpp
C02QT2UBFVH6-lm:~ gsamaras$ ./a.out
username,gpa,age00
Steven,3.2,2000
Will,3.4,1900
Ryan,3.6,1900
Tom,3,1900
But wait a minute, so now it works, but why this:
while(getline(infile, data));
{
...
}
didn't?
Because, putting a semicolon after a loop is equivalent to this:
while()
{
;
}
because as you probably already know loops with only one line as a body do not require curly brackets.
And what happened to what I thought it was the body of the loop (i.e. the part were you use std::stringstream)?
It got executed! But only once!.
You see, a pair of curly brackets alone means something, it's an anonymous scope/block.
So this:
{
stringstream ss(data);
ss >> arrayData[i].username;
ss >> arrayData[i].gpa;
ss >> arrayData[i].age;
i++;
}
functioned on its one, without being part of the while loop, as you intended too!
Any why did it work?! Because you had declared i before the loop! ;)
I'm trying to write my own vocabulary with a test for my little brother, but I have a problem when I want to read data from file into two arrays - first with English words, and second with Polish words. File looks alike
black - czarny
red - czerwony etc.
And my function:
void VOC::readout()
{
fstream file;
VOC *arr = new VOC;
string line;
file.open("slowka.txt");
if(file.good())
{
int i=0;
while(!file.eof())
{
getline(file, line);
size_t pos = line.find(" - ");
int position = static_cast<int>(pos);
file>>arr[i].en;
file>>arr[i].pl;
++i;
}
}
}
I thought it could be a good idea to insert a line into first array until the function finds " - ", and after that insert the rest of line into second array, but I have some problems with that. Could someone help me? I know I can solve it by using std::vector but I care to do that by using arrays.
If you insist on using plain arrays, you'll first have to count the number of lines in your file and then allocate enough memory. Arrays -- unlike std::vector objects -- won't grow automatically but have a fixed size.
That being said, note that using !file.eof() is not the best way to read a stream until the end is reached. You can use the simpler
std::string line;
while (std::getline(file, line)) {
// ...
}
idiom instead, which also takes care of error conditions. See this question (and corresponding answers) for more information on that.
I'm reading in from a .txt file that looks something along the lines of:
int string string string
int string string
int string string string string string
where the number of string types after each int is unknown. Each line represents a new group of values and each group needs to be into their own array value or whatever (don't know if I've worded that correctly but I hope you'll understand what I mean).
Is there a check I can perform so see if the incoming data from the file is an int so that if this is true and can tell my program its a new group of data?
I've tried
int check
if(check = file1.peek()){//start new group assignment}
but this doesn't appear to work. I need to be able to use the int value once I have found that it is the next data type being read in.
Thanks in advance.
There are several ways to do this, however I would suggest that maybe your groups are on separate lines, and the spaces within a line delimit items within a group correct?
So I would read the file, line-at-a-time and then split each line on spaces.
Let me know if the above fits and then we can explain how to do it.
Ok so you can use getline:
while (cin.good()) // reading from standard input until EOF
{
String line_str;
getline(cin, line_str); // get next line from standard input
istringstream line(line_str); // put line into string stream
if (line.good()) // read from string stream until EOF
{
int x;
line >> x; // read an integer from string stream
while (line.good()) // read from string stream until EOF
{
string s;
line >> s; // read strings from string stream
/// process s
}
}
}
I need to make a program in C++ that must read and write text files line by line with an specific format, but the problem is that in my PC I work in Windows, and in College they have Linux and I am having problems because of line endings are different in these OS.
I am new to C++ and don't know could I make my program able read the files no matter if they were written in Linux or Windows. Can anybody give me some hints? thanks!
The input is like this:
James White 34 45.5 10 black
Miguel Chavez 29 48.7 9 red
David McGuire 31 45.8 10 blue
Each line being a record of a struct of 6 variables.
Using the std::getline overload without the last (i.e. delimiter) parameter should take care of the end-of-line conversions automatically:
std::ifstream in("TheFile.txt");
std::string line;
while (std::getline(in, line)) {
// Do something with 'line'.
}
Here's a simple way to strip string of an extra "\r":
std::ifstream in("TheFile.txt");
std::string line;
std::getline(input, line));
if (line[line.size() - 1] == '\r')
line.resize(line.size() - 1);
If you can already read the files, just check for all of the newline characters like "\n" and "\r". I'm pretty sure that linux uses "\r\n" as the newline character.
You can read this page: http://en.wikipedia.org/wiki/Newline
and here is a list of all the ascii codes including the newline characters:
http://www.asciitable.com/
Edit: Linux uses "\n", Windows uses "\r\n", Mac uses "\r". Thanks to Seth Carnegie
Since the result will be CR LF, I would add something like the following to consume the extras if they exist. So once your have read you record call this before trying to read the next.
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
If you know the number of values you are going to read for each record you could simply use the ">>" method. For example:
fstream f("input.txt" std::ios::in);
string tempStr;
double tempVal;
for (number of records) {
// read the first name
f >> tempStr;
// read the last name
f >> tempStr;
// read the number
f >> tempVal;
// and so on.
}
Shouldn't that suffice ?
Hi I will give you the answer in stages. Please go trough in order to understand the code.
Stage 1: Design our program:
Our program based on the requirements should...:
...include a definition of a data type that would hold the data. i.e. our
structure of 6 variables.
...provide user interaction i.e. the user should be able to
provide the program, the file name and its location.
...be able to
open the chosen file.
...be able to read the file data and
write/save them into our structure.
...be able to close the file
after the data is read.
...be able to print out of the saved data.
Usually you should split your code into functions representing the above.
Stage 2: Create an array of the chosen structure to hold the data
...
#define MAX 10
...
strPersonData sTextData[MAX];
...
Stage 3: Enable user to give in both the file location and its name:
.......
string sFileName;
cout << "Enter a file name: ";
getline(cin,sFileName);
ifstream inFile(sFileName.c_str(),ios::in);
.....
->Note 1 for stage 3. The accepted format provided then by the user should be:
c:\\SomeFolder\\someTextFile.txt
We use two \ backslashes instead of one \, because we wish it to be treated as literal backslash.
->Note 2 for stage 3. We use ifstream i.e. input file stream because we want to read data from file. This
is expecting the file name as c-type string instead of a c++ string. For this reason we use:
..sFileName.c_str()..
Stage 4: Read all data of the chosen file:
...
while (!inFile.eof()) { //we loop while there is still data in the file to read
...
}
...
So finally the code is as follows:
#include <iostream>
#include <fstream>
#include <cstring>
#define MAX 10
using namespace std;
int main()
{
string sFileName;
struct strPersonData {
char c1stName[25];
char c2ndName[30];
int iAge;
double dSomeData1; //i had no idea what the next 2 numbers represent in your code :D
int iSomeDate2;
char cColor[20]; //i dont remember the lenghts of the different colors.. :D
};
strPersonData sTextData[MAX];
cout << "Enter a file name: ";
getline(cin,sFileName);
ifstream inFile(sFileName.c_str(),ios::in);
int i=0;
while (!inFile.eof()) { //loop while there is still data in the file
inFile >>sTextData[i].c1stName>>sTextData[i].c2ndName>>sTextData[i].iAge
>>sTextData[i].dSomeData1>>sTextData[i].iSomeDate2>>sTextData[i].cColor;
++i;
}
inFile.close();
cout << "Reading the file finished. See it yourself: \n"<< endl;
for (int j=0;j<i;j++) {
cout<<sTextData[j].c1stName<<"\t"<<sTextData[j].c2ndName
<<"\t"<<sTextData[j].iAge<<"\t"<<sTextData[j].dSomeData1
<<"\t"<<sTextData[j].iSomeDate2<<"\t"<<sTextData[j].cColor<<endl;
}
return 0;
}
I am going to give you some exercises now :D :D
1) In the last loop:
for (int j=0;j<i;j++) {
cout<<sTextData[j].c1stName<<"\t"<<sTextData[j].c2ndName
<<"\t"<<sTextData[j].iAge<<"\t"<<sTextData[j].dSomeData1
<<"\t"<<sTextData[j].iSomeDate2<<"\t"<<sTextData[j].cColor<<endl;}
Why do I use variable i instead of lets say MAX???
2) Could u change the program based on stage 1 on sth like:
int main(){
function1()
function2()
...
functionX()
...return 0;
}
I hope i helped...