i have a text file that has the numbers on one line like (no spaces between commas):
-1,5,-3,10,500000,-6000
so far this is the code i have but i am not getting anything back at all in the vector array
fstream fp;
vector<int> numbers;
int number;
fp.open("numbers.txt", ios::in | ios::binary);
if(fp.is_open()){
while(fp >> number){
numbers.push_back(number);
}
}
fp.close();
cout << "Numbers:\n";
for (int i=0; i < numbers.size(); i++) {
cout << numbers[i] << '\n';
}
i feel like im just not reading the file properly or the whole line is just getting put into the number var. Also, the number of numbers in the file is unknown so i would like to stay away from hardcoding it
fstream fp;
vector<int> numbers;
int number;
fp.open("numbers.txt", ios::in | ios::binary);
if(fp.is_open()){
while(fp >> number){
numbers.push_back(number);
fp.get();
}
}
fp.close();
cout << "Numbers:\n";
for (int i=0; i < numbers.size(); i++) {
cout << numbers[i] << '\n';
}
You just forgot about the comma's! use fp.get(); to get rid of them, and then it'll work fine :D
First of all, your input file is not binary - don't use ios::binary.
Second of all, you need to split your input tokens. Your input operation will fail every time you stumble upon a comma. You might need to input a character or a string to deal with those.
Your input fails when it trys to insert a , into an integer. You should use getline to insert the values up until the comma delimiter:
while (std::getline(fp, number, ','))
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Like this
if(fp.is_open()){
while(fp >> number){
numbers.push_back(number);
char dummy_variable_for_the_comma;
fp >> dummy_variable_for_the_comma; // read and discard a comma
}
}
You have to tell the computer to skip the commas, it won't do that for you.
Related
I am writing a program that reads in data from a file. The file contains lines of integers, such as
5 6 2 8 6 7
2 5 3
4 0 9 1 3
The first integer of each line corresponds to how many numbers there are in that line. My goal is to read in each line, store the numbers in a vector, and do some operation on them. Here is what I have done:
int main(){
vector<int> vec;
int amount;
int nums;
ifstream file ("file.txt");
while(!(file.eof())){
file >> amount;
cout << amount << endl;
for (int i = 0; i < amount; i++){
file >> nums;
vec.push_back(nums);
}
printArray(vec);
bubbleSort(vec);
vec.clear();
}
return 0;
}
Unfortunately, the last line always gets read twice. I looked online and saw that the eof() function should not be used to maintain loops. What else could I use in this situation?
Thanks.
operator>> sets the stream's eofbit flag if it tries to read past EOF. You can use that condition to break your loops. But you have to actually perform a read operation BEFORE you can evaluate eof(). See Why is iostream::eof inside a loop condition (i.e. `while (!stream.eof())`) considered wrong? for more details on that.
Since you are dealing with line-based text, you can use std::getline() to read each line first, and then you can use std::istringstream to parse each line, eg:
int main()
{
vector<int> vec;
ifstream file ("file.txt");
string line;
while (getline(file, line)) {
istringstream iss(line);
int amount, nums;
iss >> amount;
cout << amount << endl;
for (int i = 0; (i < amount) && (iss >> nums); ++i){
vec.push_back(nums);
}
printArray(vec);
bubbleSort(vec);
vec.clear();
}
return 0;
}
Alternatively, you can simply take advantage of the fact that operator>> skips whitespace, including line breaks, eg:
int main()
{
vector<int> vec;
int amount, nums;
ifstream file ("file.txt");
while (file >> amount) {
cout << amount << endl;
for (int i = 0; (i < amount) && (file >> nums); ++i){
vec.push_back(nums);
}
printArray(vec);
bubbleSort(vec);
vec.clear();
}
return 0;
}
Although, this approach would be a little less resilient to errors in the input data, compared to the std:getline() approach. If the actual amount of numbers in a given line does not match the specified amount at the beginning of the line, this approach will get its reading of the file out of sync. Worse, if a given line contains any non-integer values, this approach will fail to read any subsequent data at all.
In the std:getline() approach, if a given line is malformed, the code will simply move on to the next line and continue on like nothing bad happened.
I am working on reading in from a file and parsing through data from command line argument for homework. And I ran in a wall and I do not know what's the problem, and I hope I could get some advice on what I am missing.
The data file is composed thusly; on the first line, it has number of total lines. For each line after that, it is a line of string separated by | character. I need the '|' character because I want to split my string into substrings.
Here is an example of input file.
3
league of legends|Teemo|Master Yi|Vayne
apple|samsung|smart phone|smart watch
overwatch|d.va|junkrat|Reinhart
Here is my code.
int main( int argc, char* const argv[] )
{
//change string to char* so I can check through each char to see if the
//thing I read in is '|' character.
String Data = (argv[1]);
ifstream fin (Data.c_str());
//check whether the file is open.
if ( !fin.is_open() )
{
cout << "Could not open file" << endl;
}
else
{
int dataLines;
char dataBuffer[100];
//The first integer I read in will be how many lines I will loop through
fin >> dataLines;
//ignore the new line character and do not include it in the count of
//dataLines.
fin.ignore();
//use noskipws so I can recognize whitespaces.
fin >> noskipws >> dataBuffer;
//TEST CODE: COMMENTED OUT FOR NOW.
//cout<<dataBuffer<<endl;
//loop for the number of lines
for(int i = 0; i < dataLines; i++)
{
fin.getline(dataBuffer, 100);
//print the buffer for checking
cout<<dataBuffer<<endl;
}
}
//close the file.
fin.close();
return 0;
}
The result is supposed to look like this.
league of legends|Teemo|Master Yi|Vayne
apple|samsung|smart phone|smart watch
overwatch|d.va|junkrat|Reinhart
The actual result looks like this
of legends|Teemo|Master Yi|Vayne
apple|samsung|smart phone|smart watch
overwatch|d.va|junkrat|Reinhart
The first word that I read in from buffer is gone. "league" is the one that is missing, and I tried to see what the problem is by inserting the test code at the location specified in my code. With the given test code, my output is
league
of legends|Teemo|Master Yi|Vayne
apple|samsung|smart phone|smart watch
overwatch|d.va|junkrat|Reinhart
So the problem is that between reading in the file with noskipws and the forloop that loops over dataLine. Before the forloop my buffer is league. Yet once I enter the loop it is passed that and goes straight to of.
What am I missing here? What could be a possible solution?
Main problem:
fin >> noskipws >> dataBuffer;
Does two things. 1. >> noskipws turns off automatically skipping whitespace, unnecessary because of how OP is reading the stream. 2. >> dataBuffer reads the first word from the stream, in this case consuming the word "league"
Solution: Don't do this.
Other problems:
fin.ignore();
will ignore exactly one character. But what if someone left a nigh-invisible space after the count? Instead use
fin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
to ensure the rest of the line is consumed in its entirity.
char dataBuffer[100];
Why make yourself suffer? Instead use
std::string dataBuffer;
Recommendation:
Use std::stringstream and std::getline to tokenize the lines on '|'
std::stringstream stream(databuffer);
std::string token;
while (std::getline(stream, token, '|')
{
std::cout << token << ',';
}
You do not need the following line:
fin >> noskipws >> dataBuffer;
Tested with g++ 4.8.3 2 on RHEL 7.1
Thanks User 4581301. It reads in the data correctly and split with '|' character. Now I can work on storing the data into classes.
for anyone who may have same problem, this is the fixed up version of code.
int main( int argc, char* const argv[] )
{
String Data = (argv[1]);
ifstream fin (Data.c_str());
if ( !fin.is_open() )
{
cout << "Could not open file" << endl;
}
else
{
int dataLines;
char dataBuffer[100];
fin >> dataLines;
fin.ignore();
for(int i = 0; i < dataLines; i++)
{
while(fin.getline(dataBuffer, 100, '|'))
{
cout<<dataBuffer<<endl;// check to see if it reads in correctly.
}
}
}
fin.close();
return 0;
}
I am quite new in c++ and programming so sorry in advance in my question repeats. I have a text file of 3 lines:
7
00000000000000000000000*0000
0 0 0 R 0
What I need to do is read 2nd line and write it into an array as char. But I must not include 3rd line because it will go to a completely different matrix. My code so far :
ifstream input;
input.open("input1.txt");
input >> start;
char a=0;
string line;
while (getline(input, line))
{
a=0;
istringstream iss(line);
int length = line.size();
for (int i=0; i<length; i++)
{
iss >> a;
A[i] = a;
cout << A[i] << " " << i << endl;
}
}
input.close();
However, with this code it always starts new array for 3rd line. What am I doing wrong? What is the easiest way to fix it? Thank you.
-----------------------------Update--------------------------------------
I have modified the code but it still does not work properly. I am getting this kind of result : 5)-└ instead of correct one. My current code:
void Read(int &numLines, int &start, vector<char>&A, char B[][5])
{
ifstream input;
input.open("input.txt");
input >> start;
input.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
string line;
if(getline(input, line))
{
for(char temp: line)
{
A.push_back(temp);
}
}
input.close();
}
A here is a vector I want to write 2nd line to, char by char
Start is just an integer in which I am storing 1st line (7)
Thank you very much for advices
Mixing >> and std::getline is non-trivial. For example, after input >> start; the end of line marker is left in the stream in case it's still needed. In your case it isn't, and it is picked off by the subsequent call to getline, resulting in a read of an empty line.
This is what's complicating your read of line and forcing the while loop and test for empty lines.
Step through your program with your development environment's debugger and you'll see what I'm talking about. Get used to using the debugger. It's possibly the best programming productivity tool you'll ever encounter.
The easiest way to fix it is to place
input.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
after
input >> start;
to eat up the end of the line (and anything else that might be on that line. This needs the addition of #include<limits> to get std::numeric_limits<std::streamsize>::max.
Then you can remove the while loop and replace it with
if (getline(input, line))
No loop, not chance of consuming multiple lines from the file. And the logic for reading and processing the third line can follow.
Side note: instead of that for loop, consider
int i = 0;
while (iss >> a)
{
A[i] = a;
cout << A[i] << " " << i << endl;
i++;
}
This will march through iss until it hits the end of the line. You can also throw iss out entirely and just read the characters directly out of line.
int i = 0;
for(char temp: line)
{
A[i] = temp;
}
And A should probably be a vector if it isn't already to reduce the chances of buffer overruns.
for(char temp: line)
{
A.push_back(temp);
}
I would go with something like this:
std::string start;
std::string Astring;
ifstream input;
input.open("input.txt");
input >> start;
input >> Astring;
// If you really want a char array
char * A = new char[Astring.size()];
for (unsigned int i = 0; i < Astring.size(); i++) {
A[i] = Astring[i];
}
// Don't forget to delete after use
delete[] A;
Moreover, if you just need the char array as an input to something else later, you can call Astring.c_str() instead of that for loop, which returns a C-style char array.
I have problem with the following code:
#include<iostream>
using namespace std;
int main()
{
char a[200];
int i;
for (i = 0; cin.get() != '\n'; i++) {
cin >> a[i];
}
cout << i;
system("pause");
return 0;
}
I don't know why when i input without space 10 char for example. i si equal to 10/2=5 ?
You discard every odd symbol, cin.get() read symbol 1,
cin >> read symbol two, and again cin.get() read symbol 3,
and cin >> read symbol 4 from standard input.
You are throwing out half of your cin results.
When you use cin, a character is read, but you are not assigning it to anything inside the for loop criteria; only inside the loop body are you saving it.
Inside the loop, you read in another character (after the one you already read in during the loop's test criteria) and assign that one. The loop repeats, and the next character read is again thrown away with the line cin.get() != '\n' because you are not assigning the results to anything. And this continues, alternating characters you throw away with characters you "save" into the array.
You get two characters, once increment i variable and only second of them insert in array
int main()
{
char a[200];
int i;
\\ cin.get() - get one char and insert it in a[i]
\\ after that, compare this value with '\n'
\\ if equal, break the loop, if different, continue
for (i = 0; (a[i] = cin.get()) != '\n'; i++);
\\ last character ('\n') should be replaced with '\0'
a[i]='\0';
cout << i;
system("pause");
return 0;
}
while solution:
int main()
{
char a[200];
int i=0;
cin >> a[i];
while (a[i] != '\n')
{
i++;
cin >> a[i];
}
a[i]='\0';
cout << i;
system("pause");
return 0;
}
do - while solution:
int main()
{
char a[200];
int i=0;
do
{
cin >> a[i];
}
while(a[i++]!='\n');
a[i-1]='\0';
cout << i-1;
system("pause");
return 0;
}
As a matter of fact, you are reading the standard input (std::cin) in two different ways, storing its output only once every two character extractions.
std::basic_istream::get (cin.get()) extracts character or characters from stream. Once extracted, whey are forgotten, sent to limbo. You simply ignore them. Which is not what I suspect you want to do.
std::basic_istream::operator>> (cin >> ...) also extracts character or characters (following the type of the right hand side operand).
So, with an input of ten characters, you ignore five of them in your for condition check and store five in the loop block.
A correct way to read the characters would be to use std::getline (en.cppreference.com/w/cpp/string/basic_string/getline):
std::string input;
std::getline(cin, input);
std::cout << input << std::endl;
This example code will simply read a line and output it, verbatim, in the standart output.
I have a file that has a number in which is the number of names that follow. For example:
4
bob
jim
bar
ted
im trying to write a program to read these names.
void process_file(ifstream& in, ofstream& out)
{
string i,o;
int tmp1,sp;
char tmp2;
prompt_user(i,o);
in.open (i.c_str());
if (in.fail())
{
cout << "Error opening " << i << endl;
exit(1);
}
out.open(o.c_str());
in >> tmp1;
sp=tmp1;
do
{
in.get(tmp2);
} while (tmp2 != '\n');
in.close();
out.close();
cout<< sp;
}
So far I am able to read the first line and assign int to sp
I need sp to be a counter for how many names. How do I get this to read the names.
The only problem I have left is how to get the names while ignoring the first number.
Until then i cannot implement my loop.
while (in >> tmp1)
sp=tmp1;
This successfuly reads the first int from the and then tries to continue. Since the second line is not an int, extraction fails, so it stops looping. So far so good.
However, the stream is now in fail state, and all subsequent extractions will fail unless you clear the error flags.
Say in.clear() right after the first while loop.
I don't really see why you wrote a loop to extract a single integer, though. You could just write
if (!(in >> sp)) { /* error, no int */ }
To read the names, read in strings. A loop is fine this time:
std::vector<std::string> names;
std::string temp;
while (in >> temp) names.push_back(temp);
You'd might want to add a counter somewhere to make sure that the number of names matches the number you've read from the file.
int lines;
string line;
inputfile.open("names.txt");
lines << inputfile;
for(i=0; i< lines; ++i){
if (std::getline(inputfile, line) != 0){
cout << line << std::endl;
}
}
First of all, assuming that the first loop:
while (in >> tmp1)
sp=tmp1;
Is meant to read the number in the beginning, this code should do:
in >> tmp1;
According to manual operator>>:
The istream object (*this).
The extracted value or sequence is not returned, but directly stored
in the variable passed as argument.
So don't use it in condition, rather use:
in >> tmp1;
if( tmp1 < 1){
exit(5);
}
Second, NEVER rely on assumption that the file is correctly formatted:
do {
in.get(tmp2);
cout << tmp2 << endl;
} while ( (tmp2 != '\n') && !in.eof());
Although whole algorithm seems a bit clumsy to me, this should prevent infinite loop.
Here's a simple example of how to read a specified number of words from a text file in the way you want.
#include <string>
#include <iostream>
#include <fstream>
void process_file() {
// Get file name.
std::string fileName;
std::cin >> fileName;
// Open file for read access.
std::ifstream input(fileName);
// Check if file exists.
if (!input) {
return EXIT_FAILURE;
}
// Get number of names.
int count = 0;
input >> count;
// Get names and print to cout.
std::string token;
for (int i = 0; i < count; ++i) {
input >> token;
std::cout << token;
}
}