I created a very simple code, but the push_back function doesn't want to work. It gives me an absolutely different result than expected.
Here is the code:
std::vector<std::string> words;
std::ifstream infile ("words.txt");
std::string temp;
while (std::getline(infile, temp))
{
words.push_back(temp);
}
for (std::size_t i = 0; i < words.size(); i++)
{
std::cout << words[i] << " ";
}
The "words.txt" file contains only 4 words:
window
tyre
give
speaker
The result is supposed to be "window tyre give speaker", but for me it is " speaker".
What is the problem?
This proved to be the underlying problem:
Have you tried dumping the input file (e.g. with hexdump -C or similar) to check for rogue control sequences such as \r which might explain the behaviour which you are seeing.
Your input file might be a text file from a DOS/Windows-like system and you might be using a Unix-like system.
Related
I've been googling this question for a few hours and can't seem to find anything that addresses it.
I'm reeaaaally hazy on file operations in C++, but I've spent about 20 of the last 36 hours reading documentation and forum questions trying to get a project for a friend together.
Say I've got a file called raw_questions.txt, and I'd like to make some changes to it. This file is a study guide for an exam, and has a question followed by 4 multiple-choice answers. I want to remove blank lines and add some tokens to allow another program I'm working on to parse it. I've written a formatter program to perform those operations. The operations are:
Remove blank lines from source file as it appears it's double-spaced
Add a delimiter character ('#') to the end of each question and
answer.
Using the delimiter, read each question and answer in as a string
and append it to an output file with a token at the beginning of
question or answer, which will let my other program know whether a
line contains a question or answer.
My question: I'm stuck at how to move from one operation to the next. My current approach is to read each line into a string, perform the operation on the string, and to add the new string to an output file. Using this approach, to perform the next operation I have to open the previous operation's output file as my new input file, and make a new output file for that operation. I feel like there's got to be a better way, but like I said, I'm pretty hazy on file operations in C++. What should I be doing in this situation?
I've considered creating an ifstream and ofstream that both point to the same file, and hoping that when the ifstream file is opened, it will store a temporary copy in memory. Then, after I read line by line and write to my ofstream object, when it closes it will overwrite my old file. I don't know if that makes any sense, and I don't think that's even how fstream works.
The code that I have so far:
#include <fstream>
#include <string>
#include "Debug.h"
Debug debugger;
void remove_empty_lines (std::ifstream& input, std::ofstream& output);
void insert_delimiter (std::ifstream& input, std::ofstream& output, char delimiter);
void create_output (std::ifstream& input, std::ofstream& output);
int main() {
debugger.set_active();
char delimiter = '#';
std::ifstream input;
std::ofstream output;
input.open("questions_source.txt");
output.open("questions_intermidiate.txt");
remove_empty_lines (input, output);
}
void remove_empty_lines (std::ifstream& input, std::ofstream& output) {
while (!input.eof()) {
std::string line;
std::getline(input, line);
if (line != "") {
output << line << std::endl;
}
}
}
void insert_delimiter(std::ifstream& input, std::ofstream& output) {
}
// This function doesn't quite work, WIP - Please ignore
void create_output(std::ifstream& input, std::ofstream& output) {
std::string line;
for (int i = 1; !input.eof(); i++) {
debugger.out("Inserting tokens.");
bool found = false;
while (!found) {
getline (input, line);
if (i < 10) {
if (line[1] == ')') {
line.erase (0, 3);
output << "[" << i << "]" << line << std::endl;
debugger.out("Found line: " + line);
found = true;
}
} else if (i < 100) {
if (line[2] == ')') {
line.erase (0, 4);
output << "[" << i << "]" << line << std::endl;
debugger.out("Found line: " + line);
found = true;
}
}
}
for (int j = 0; j < 4; j++) {
getline (input, line);
if (line[1] == ')') {
line.erase (0, 3);
output << "[" << i << "a]" << line << std::endl;
}
}
}
}
I'm also trying to teach myself git at the moment, so I happen to have the project I'm working on hosted on github here. I don't know if the context will make what I'm trying to do make sense, but I'm posting it just in case.
Bonus question: I've been racking my brain, but I haven't come up with a solution to adding the delimiter. Answers seem to be one line long, so I can probably just add the delimiter to the end of any line starting with "A)" etc., but some of the questions are much longer. My thought is to find any occurrence of "A)" and add the delimiter to the end of the line above it, but I can't think of how to do that. Can anyone point me in the right directions for member functions of fstream that might help?
Thanks for reading.
Streams do not magically read the entire file into memory. If that is what you want to do, you should just do that: my guess is that your file is considerably smaller than your available memory, and it might be easier to perform all the operations in place using standard C++ containers.
Lets say I have a text file containing something like:
Four
score
and
seven
years
ago
...
I want to be able to label these lines so that after the program runs, the file looks like:
1.Four
2.score
3.and
4.seven
5.years
6.ago
...
I've prepared a solution; however, I find it to be heavy weight and it has a problem of labeling one past the last line...
std::string file = "set_test - Copy.txt";
std::ifstream in_test{file};
std::vector<std::string> lines;
while(in_test) {
std::string temp;
getline(in_test, temp);
lines.push_back(temp);
}
in_test.close();
std::ofstream out_test{file};
for(unsigned int i = 0; i < lines.size(); ++i) {
out_test << i+1 << '.' << lines[i] << '\n';
}
On top of being heavy-weight, this solution also labels the line beyond the last line of text.
Does anyone have a better solution to this problem?
The cause of your problem is this structure
while (stream is good)
read from stream
do something
as it will read too much. (See this Q&A for explanation.)
What's happening is that the very last getline, the one that actually reaches the end of the file, will fail and leave temp empty.
Then you add that empty line to your lines.
The "canonical" stream-reading loop structure is
while (attempt to read)
do something with the result
in your case,
std::string temp;
while (getline(in_test, temp)) {
lines.push_back(temp);
}
If you write to a different file you don't need to store anything except the last line; you can write each line immediately.
If you want to replace the original, you can replace the old with the new afterwards.
Something like this:
std::ifstream in_test{"set_test - Copy.txt";}
std::ofstream out_test{"set_test - Numbered.txt"};
if (!in_test || !out_test) {
std::cerr << "There was an error in the opening of the files.\n";
return;
}
int i = 1;
std::string line;
while (getline(in_test, line) && out_test << i << '.' << line << '\n') {
i++;
}
I am writing a code to check to see if one document (text1.txt) contains a list of banned words (bannedwords.txt) in it.
For example, the text1 document contains lyrics to a song and i want to check whether the word pig from the banned document is included in it. I then want the out put to be similar to:
"pig" found 0 times
"ant" found 3 times
This is what I have come up with so far but cannot seem to put the array of banned words into the search. Any help would be amazing :D
Thanks Fitz
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
bool CheckWord(char* filename, char* search)
{
int offset;
string line;
ifstream Myfile;
Myfile.open(filename);
if (Myfile.is_open())
{
while (!Myfile.eof())
{
getline(Myfile, line);
if ((offset = line.find(search, 0)) != string::npos)
{
cout << "The Word " << search<< " was found" << endl;
return true;
}
else
{
cout << "Not found";
}
}
Myfile.close();
}
else
cout << "Unable to open this file." << endl;
return false;
}
int main()
{
ifstream file("banned.txt");
if (file.is_open())//file is opened
{
string bannedWords[8];//array is created
for (int i = 0; i < 8; ++i)
{
file >> bannedWords[i];
}
}
else //file could not be opened
{
cout << "File could not be opened." << endl;
}
ifstream text1;//file is opened
text1.open("text1.txt");
if (!text1)//if file could not be opened
{
cout << "Unable to open file" << endl;
}
CheckWord("text1.txt", "cat");
system("pause");
}
Your main() function is reading the contents of banned.txt into an array of 8 std::string named bannedWords.
The array bannedWords is not being used anywhere after that. C++ doesn't work by magic, and compilers are not psychic so cannot read your mind in order to understand what you want your code to do. If an array (or its elements) are not accessed anywhere, they will not be used to do what you want with them.
You need to pass strings from the bannedWords array to CheckWord(). For example;
CheckWord("text1.txt", bannedWords[0].c_str());
will attempt to pass the contents of the first string in bannedWords to CheckWord().
However, that will not compile either unless you make the second parameter of CheckWord() (named search) be const qualified.
Or, better yet, change the type of the second argument to be of type std::string. If you do that, you can eliminate the usage of c_str() in the above.
I don't claim that is a complete solution to your problem - because there are numerous problems in your code, some related to what you've asked about, and some not. However, my advice here will get you started.
Your question is really vague; it looks like you need to spend some time to pin down your program structure before you could ask for help here.
However, since we were all new once, here's a suggestion for a suitable structure:
(I'm leaving out the file handling bits because they're irrelevant to the essential structure)
//Populate your array of banned words
std::string bannedWords[8];
int i;
for (int i = 0; i < 8; ++i)
{
file >> bannedWords[i];
}
//Load the entire file content into memory
std::ifstream in("text1.txt");
std::string fileContents((std::istreambuf_iterator<char>(in)), std::istreambuf_iterator<char>());
So now the entire file content is in the string "fileContents", and the 8 banned words are in "bannedWords". I suggest this approach because otherwise you're opening, reading, and closing the file for every word. Hardly a good design.
Now you've got to check each word against the file content. There's some more sophisticated ways to do this, but your simplest option is a loop.
//Loop through each banned word, and check if it's in the file
for (int i = 0; i < 8; i++)
{
if (fileContents.find(bannedwords[i]) != std::string::npos)
{
//Do whatever
}
}
Obviously you'll need to do the find a little differently if you want to count the number of occurrences, but that's another question.
I have to create a program that will output various information about 1343 runners in a marathon. I'm having to import the data from a csv spreadsheet, so I chose to use the getline function. I use simple recursion to fill a string array and then simply use recursion once more to output the data. But for some reason, it only wants to display 300 or so runners' data. Here's the code:
int main(){
string data[1344];
vector<string> datav;
string header;
ifstream infile("C:\\Users\\Anthony\\Desktop\\cmarathon.csv");
int i = 0;
if (infile.is_open()) {
for (i=0; i<=1343; i++) {
getline(infile, data[i]);
}
datav.assign(data, data+1344);
for (int i = 0; i < datav.size(); i++) {
cout << datav[i] << "\n";
}
}
}
I attempted to use a vector in hopes it would help to allocate the required memory to execute the program properly (if that is in fact the problem here).
That code yields the perfect output of runners 1045-1343. I've tried simple work arounds, such as using several for() loops to combine the output seamlessly to no avail. Any information would be appreciated.
You do not need to copy from the array to the vector. You can add to the vector directly instead. Also, it is somewhat bad practice to shadow another local variable at the outer scope.
int main(){
string line;
vector<string> datav;
string header;
ifstream infile("C:\\Users\\Anthony\\Desktop\\cmarathon.csv");
if (infile.is_open()) {
// Are you supposed to read the header line first?
getline( infile, header );
while( getline( infile, line ).good() )
datav.push_back( line );
cout << "Container has " << datav.size() << " lines\n";
for (size_t i = 0; i < datav.size(); i++) {
cout << datav[i] << "\n";
}
}
}
Of course, you still have to break down each line to the individual fields, so pushing back a class or struct as EToreo suggested would be a good idea.
You should try using a struct to represent the fields in the CSV file and then make a vector of that struct type.
Now, loop through the file, reading each line till you reach the end of the file (Google how to do that) - DO NOT assume 1343, you don't have to. When you read in each line, create a new object from your struct and fill it with the content of that line (you will need to parse it by reading till a tab (\t) or the end of the string) and then datav.push(newObj) it onto your vector.
I suggest using the correct type's in your struct (int for age, string for name, etc.) and passing the string values from the file into those types. It will be much easier to do things like make a sum of everyone's age. You will thank yourself (and maybe me?) later.
If your not needing to use a vector:
for (i=0; i<=1343; i++) {
cout << data[i] << endl;
}
should work to print out whatever is in the data array
It is also possible to specify a delimeter for the getline function if you need to put different strings in different variables.
However EToreo's method may be more useful to you in the long run.
This may be a very simplistic question, but I have not found any examples to guide me. I am trying to write class in C++ that can read a text file where columns of data (float, char, int, etc...) are separated by spaces. I would like the class to be able to ignore some columns and read in specified columns. For now I am experimenting with one and two column formats and progressing from there. A brief example of a test input file is listed below.
103.816
43.984
2214.5
321.5
615.8
8.186
37.6
My first attempt at writing a code to read in one column of data is trivial and looks like this.
void Read_Columnar_File::Read_File(const std::string& file_name)
{
int i;
std::ifstream inp(file_name,std::ios::in | std::ios::binary);
if(inp.is_open()) {
std::istream_iterator<float> start((inp)), end;
std::vector<float> values(start,end);
for(i=0; i < 7; i++) std::cout << values[i] << std::endl;
}
else std::cout << "Cannot Open " << file_name << std::endl;
inp.close();
}
In my next attempt I am trying to read in only one column of a two column format like the input shown below. The numbers are just made up for this example
103.816 34.18
43.984 21.564
2214.5 18.5
321.5 1.00
615.8 4.28
8.186 1.69
37.6 35.48
I modified the code format slightly to look like the example below. I am using a brief but of pseudocode after the inp >> statement to illustrate that I am trying to get the code to skip to the next line after reading in the first column. my question is "How do I get the code to just read the first column and then skip to the next line where again it just reads the first column of data and make it keep doing this until the end of file?" And thank you in advance for any advice that you can give.
void Read_Columnar_File::Read_File(const std::string& file_name)
{
int i;
float input;
std::vector<float> values;
std::ifstream inp(file_name,std::ios::in | std::ios::binary);
if(inp.is_open()) {
for(i=0; i < 7; i++) {
inp >> input >> \\ - At this point I want the code to skip to the next
\\ line of the input file to only read the first column
\\ of data
values.push_back(input);
}
for(i=0; i < 7; i++) std::cout << values[i] << std::endl;
}
else std::cout << "Cannot Open " << file_name << std::endl;
inp.close();
}
You can use the member function ignore() to discard all the characters until the next line. I would also fix up your code to use a for() loop predicated on the success of the extraction so your code will work for any number of columns, not just 7:
for (float input; inp >> input; values.push_back(input))
{
inp.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
When you want to read only part of a line, and skip the rest of that line, one easy starting point is to:
read the entire line into a string
put the whole string into an istringstream
Parse out the parts you care about
Repeat
As a rule, I generally find this easier to generalize than ones that alternate between reading and ignoring data as it's being read from the file.