I need to write an 8 ball code that has eleven options to display and it needs to pull from a text file. I have it taking lines from the text file but sometimes it takes an empty line with no writing. And I need it to only take a line that has writing.
Here are that options it needs to draw from:
Yes, of course!
Without a doubt, yes.
You can count on it.
For sure!Ask me later.
I'm not sure.
I can't tell you right now.
I'll tell you after my nap.
No way!I don't think so.
Without a doubt, no.
The answer is clearly NO.
string line;
int random = 0;
int numOfLines = 0;
ifstream File("file.txt");
srand(time(0));
random = rand() % 50;
while (getline(File, line))
{
++numOfLines;
if (numOfLines == random)
{
cout << line;
}
}
}
IMHO, you need to either make the text lines all the same length, or use a database (table) of file positions.
Using File Positions
Minimally, create a std::vector<pos_type>.
Next read the lines from the file, recording the file position of the beginning of the string:
std::vector<std::pos_type> text_line_positions;
std::string text;
std::pos_type file_position = 0;
while (std::getline(text_file, text)
{
text_line_positions.push_back(file_position);
// Read the start position of the next line.
file_position = text_file.tellg();
}
To read a line from a file, get the file position from the database, then seek to it.
std::string text_line;
std::pos_type file_position = text_line_positions[5];
text_file.seekg(file_position);
std::getline(text_file, text_line);
The expression, text_line_positions.size() will return the number of text lines in the file.
If File Fits In Memory
If the file fits in memory, you could use std::vector<string>:
std::string text_line;
std::vector<string> database;
while (getline(text_file, text_line))
{
database.push_back(text_line);
}
To print the 10 line from the file:
std::cout << "Line 10 from file: " << database[9] << std::endl;
The above techniques minimize the amount of reading from the file.
Related
I'm trying to edit a .dat file. I want to read a line by line number, turn the content to int, edit and replace it.
like I want to edit line number 23, it says "45" I need to make it "46". How do I do that?
ofstream f2;
theBook b;
f2.open("/Users/vahidgr/Documents/Files/UUT/ComputerProjects/LibraryCpp/LibraryFiles/Books.dat", ios::app);
ifstream file("/Users/vahidgr/Documents/Files/UUT/ComputerProjects/LibraryCpp/LibraryFiles/Books.dat");
cout<<"In this section you can add books."<<endl;
cout<<"Enter ID: "; cin>>b.id;
cout<<"Enter Name: "; cin>>b.name;
string sID = to_string(b.id);
string bookName = b.name;
string line;
int lineNumber = 0;
while(getline(file, line)) {
++lineNumber ;
if(line.find(bookName) != string::npos && line.find(sID) != string::npos) {
int countLineNumber = lineNumber + 4;
registered = true;
f2.close();
break;
}
}
Inside the file:
10000, book {
author
1990
20
20
}
If your file is small (such as under 1GB), you can just read the entire file into memory line-by-line as a std::vector<std::string> (Hint: use std::getline). Then, edit the required line, and overwrite the file with an updated one.
Iterate Byte for Byte through the file and count line breaks (\n or \r\n on Windows).
After 22 breaks, insert bytes that say “46”. It should overwrite the existing bytes.
If your modifications are the exact size of the original text, you can write back to the same file. Otherwise, you will need to write your modifications to a new file.
Since your file is variable length text, separated by newlines, we'll have to skip lines until we get to the desired line:
const unsigned int desired_line = 23;
std::ifstream original_file(/*...*/);
std::ofstream modified_file(/*...*/);
// Skip lines
std::string text_line;
for (unsigned int i = 0; i < desired_line - 1; ++i)
{
std::getline(original_file, text_line);
modified_file << text_line << std::endl;
}
// Next, read the text, modify and write to the original file
//... (left as an exercise for the OP, since this was not explicit in the post.
// Write remaining text lines to modified file
while (std::getline(original_file, text_line))
{
modified_file << text_line << std::endl;
}
Remember to write your modified text to the modified file before copying the remaining text.
Edit 1: By record / object
This looks like an X-Y problem.
A preferred method is to read in the objects, modify the object, then write the objects to a new file.
I'm really stuck with this problem I'm having for reading rows and columns from a text file. We're using text files that our prof gave us. I have the functionality running so when the user in puts "numrows (file)" the number of rows in that file prints out.
However, every time I enter the text files, it's giving me 19 for both. The first text file only has 4 rows and the other one has 7. I know my logic is wrong, but I have no idea how to fix it.
Here's what I have for the numrows function:
int numrows(string line) {
ifstream ifs;
int i;
int row = 0;
int array [10] = {0};
while (ifs.good()) {
while (getline(ifs, line)) {
istringstream stream(line);
row = 0;
while(stream >>i) {
array[row] = i;
row++;
}
}
}
}
and here's the numcols:
int numcols(string line) {
int col = 0;
int i;
int arrayA[10] = {0};
ifstream ifs;
while (ifs.good()) {
istringstream streamA(line);
col = 0;
while (streamA >>i){
arrayA[col] = i;
col++;
}
}
}
edit: #chris yes, I wasn't sure what value to return as well. Here's my main:
int main() {
string fname, line;
ifstream ifs;
cout << "---- Enter a file name : ";
while (getline(cin, fname)) { // Ctrl-Z/D to quit!
// tries to open the file whose name is in string fname
ifs.open(fname.c_str());
if(fname.substr(0,8)=="numrows ") {
line.clear();
for (int i = 8; i<fname.length(); i++) {
line = line+fname[i];
}
cout << numrows (line) << endl;
ifs.close();
}
}
return 0;
}
This problem can be more easily solved by opening the text file as an ifstream, and then using std::get to process your input.
You can try for comparison against '\n' as the end of line character, and implement a pair of counters, one for columns on a line, the other for lines.
If you have variable length columns, you might want to store the values of (numColumns in a line) in a std::vector<int>, using myVector.push_back(numColumns) or similar.
Both links are to the cplusplus.com/reference section, which can provide a large amount of information about C++ and the STL.
Edited-in overview of possible workflow
You want one program, which will take a filename, and an 'operation', in this case "numrows" or "numcols". As such, your first steps are to find out the filename, and operation.
Your current implementation of this (in your question, after editing) won't work. Using cin should however be fine. Place this earlier in your main(), before opening a file.
Use substr like you have, or alternatively, search for a space character. Assume that the input after this is your filename, and the input in the first section is your operation. Store these values.
After this, try to open your file. If the file opens successfully, continue. If it won't open, then complain to the user for a bad input, and go back to the beginning, and ask again.
Once you have your file successfully open, check which type of calculation you want to run. Counting a number of rows is fairly easy - you can go through the file one character at a time, and count the number that are equal to '\n', the line-end character. Some files might use carriage-returns, line-feeds, etc - these have different characters, but are both a) unlikely to be what you have and b) easily looked up!
A number of columns is more complicated, because your rows might not all have the same number of columns. If your input is 1 25 21 abs 3k, do you want the value to be 5? If so, you can count the number of space characters on the line and add one. If instead, you want a value of 14 (each character and each space), then just count the characters based on the number of times you call get() before reaching a '\n' character. The use of a vector as explained below to store these values might be of interest.
Having calculated these two values (or value and set of values), you can output based on the value of your 'operation' variable. For example,
if (storedOperationName == "numcols") {
cout<< "The number of values in each column is " << numColsVal << endl;
}
If you have a vector of column values, you could output all of them, using
for (int pos = 0; pos < numColsVal.size(); pos++) {
cout<< numColsVal[pos] << " ";
}
Following all of this, you can return a value from your main() of 0, or you can just end the program (C++ now considers no return value from main to a be a return of 0), or you can ask for another filename, and repeat until some other method is used to end the program.
Further details
std::get() with no arguments will return the next character of an ifstream, using the example code format
std::ifstream myFileStream;
myFileStream.open("myFileName.txt");
nextCharacter = myFileStream.get(); // You should, before this, implement a loop.
// A possible loop condition might include something like `while myFileStream.good()`
// See the linked page on std::get()
if (nextCharacter == '\n')
{ // You have a line break here }
You could use this type of structure, along with a pair of counters as described earlier, to count the number of characters on a line, and the number of lines before the EOF (end of file).
If you want to store the number of characters on a line, for each line, you could use
std::vector<int> charPerLine;
int numberOfCharactersOnThisLine = 0;
while (...)
{
numberOfCharactersOnThisLine = 0
// Other parts of the loop here, including a numberOfCharactersOnThisLine++; statement
if (endOfLineCondition)
{
charPerLine.push_back(numberOfCharactersOnThisLine); // This stores the value in the vector
}
}
You should #include <vector> and either specific std:: before, or use a using namespace std; statement near the top. People will advise against using namespaces like this, but it can be convenient (which is also a good reason to avoid it, sort of!)
I'm trying to write a program that reads in a CSV file (no need to worry about escaping anything, it's strictly formatted with no quotes) but any numeric item with a value of 0 is instead just left blank. So a normal line would look like:
12,string1,string2,3,,,string3,4.5
instead of
12,string1,string2,3,0,0,string3,4.5
I have some working code using vectors but it's way too slow.
int main(int argc, char** argv)
{
string filename("path\\to\\file.csv");
string outname("path\\to\\outfile.csv");
ifstream infile(filename.c_str());
if(!infile)
{
cerr << "Couldn't open file " << filename.c_str();
return 1;
}
vector<vector<string>> records;
string line;
while( getline(infile, line) )
{
vector<string> row;
string item;
istringstream ss(line);
while(getline(ss, item, ','))
{
row.push_back(item);
}
records.push_back(row);
}
return 0;
}
Is it possible to overload operator<< of ostream similar to How to use C++ to read in a .csv file and output in another form? when fields can be blank?
Would that improve the performance?
Or is there anything else I can do to get this to run faster?
Thanks
The time spent reading the string data from the file is greater than the time spent parsing it. You won't make significant time savings in the parsing of the string.
To make your program run faster, read bigger "chunks" into memory; get more data per read. Research on memory mapped files.
One alternative way to handle this to get better performance is to read the whole file into a buffer. Then go through the buffer and set pointers to where the values start, if you find a , or end of line put in a \0.
e.g. https://code.google.com/p/csv-routine/
I am working on ubuntu. I have a file called test.txt. I would like to replace the second line with another line. How can I do that? I don't want to create a new file and delete the first one.
I would like to specify that the lenght of the new line is the same with the length of the ond one
Try something like:
#include <fstream>
#include <string>
int main() {
const int lineToReplace = 14;
std::fstream file("myfile.txt", std::ios::in | std::ios::out);
char line[255];
for (int i=0; i<lineToReplace-1; ++i)
file.getline(line, 255); // This already skips the newline
file.tellg();
file << "Your contents here" << std::endl;
file.close();
return 0;
}
Note that line can hold up to 254 bytes (plus the null terminator), so if your line takes more than that, adjust accordingly.
If the file is small enough you can read it into memory, do whatever modifications you want on the in-memory copy, and the write if back out.
Edit Code as requested:
// A vector to store all lines
std::vector<std::string> lines;
// The input file
std::ifstream is("test.txt")
// Get all lines into the vector
std::string line;
while (std::getline(is, line))
lines.push_back(line);
// Close the input file
is.close();
// All of the file is now in memory, each line a single entry in the vector
// "lines". The items in the vector can now be modified as you please.
// Replace the second line with something else
lines[1] = "Something else";
// Open output file
std::ofstream os("test.txt");
// Write all lines to the file
for(const auto& l : lines)
os << l << '\n';
// All done, close output file
os.close();
This is Python, but it's significantly more readable and terse for this purpose:
f = open('text.txt', 'w+') # open for read/write
g = tempfile.TemporaryFile('w+') # temp file to build replacement data
g.write(next(f)) # add the first line
next(f) # discard the second line
g.write(second_line) # add this one instead
g.writelines(f) # copy the rest of the file
f.seek(0) # go back to the start
g.seek(0) # start of the tempfile
f.writelines(g) # copy the file data over
f.truncate() # drop the rest of the file
You could also use shutil.copyfileobj instead of writelines to do block copying between the files.
Here's how I would do it, without a hard limit on the line length:
#include <fstream>
#include <string>
using namespace std;
int main()
{
fstream file("test.txt",std::ios::in|std::ios::out);
string line;
string line_new="LINE2";
// Skip the first line, file pointer points to beginning of second line now.
getline(file,line);
fstream::pos_type pos=file.tellg();
// Read the second line.
getline(file,line);
if (line.length()==line_new.length()) {
// Go back to start of second line and replace it.
file.seekp(pos);
file << line_new;
}
return 0;
}
I am currently developing an application, which gets the input from a text file and proceeds accordingly. The concept is the input file will have details in this fomat
A AND B
B OR C
Each and every line will be seperated by a blank space and the input must be taken from the text file and processed by logic. I use a TCPP compiler and i am facing problems reading the input. Please help me with the issue...
Reading input a line at a time is normally done with std::getline, something like this:
std::string line;
std::ifstream infile("filename");
while (std::getline(line, infile))
// show what we read
std::cout << line << "\n";
If you're having trouble with things like this, you might consider looking for a (better) book on C++ than whatever you're now (hopefully) using.
Following can be used straightaway:
BOOL ReadFile(CString filename)
{
BOOL bRead = TRUE;
std::ifstream m_strmFile;
m_strmFile.open(filename, std::ios::in);
char pszLine[256];
memset(pszLine, 256, 0);
if (m_strmFile)
{
// Read whatever number of lines in your file
for (unsigned int i = 0; i < 5/*number of lines*/; i++)
m_strmFile.getline(pszLine, 256);
// Do whatever you want to do with your read lines here...
}
else bRead = FALSE;
return bRead;
}
are you using headr files like:
include
or #include and you can make use of the fileobject.getline(), (do check its proper syntax.) function in C++ or for char by char use fileobject.get(ch) kind of function