I have a file that is opened filled like this:
STRING
INT
INT
INT
filename.txt
STRING
INT
INT
INT
filename1.txt
etcetera
I have code that is supposed to read from the file, pull the string, the integers, and the file names. It is able to pull the string and the integers, but it won't pull the file name.
Here is the code:
while( !input.eof() )
{
string name;
int type = UNKNOWN;
int pages;
float ounces;
getline( input, name );
input >> type >> pages >> ounces;
getline(input, reviewFile); //reviewFile is a static string called in the header file
input.ignore(INT_MAX, '\n');
}
It should work if you put the ignore before the getline, to eat the newline after the ounces:
while( !input.eof() )
{
string name;
int type = UNKNOWN;
int pages;
float ounces;
getline( input, name );
input >> type >> pages >> ounces;
input.ignore(INT_MAX, '\n');
getline(input, reviewFile); //reviewFile is a static string called in the header file
}
The operator>> will read words, not taking end of line into account that much.
Therefore, I would write something like this (As Massa wrote in a comment):
input >> type >> pages >> ounces >> ws;
Also, please note that "eof" checks are suboptimal. Try to avoid them. Moreover, you do not check after the reads within the loop if there is anything more to read.
Related
I need to read from file a series of information that is separated by commas
example
Orionis, 33000, 30000, 18, 5.9
Spica, 22000, 8300, 10.5, 5.1
i'm having a hard time figuring out the getline structure to make this work. The CS tutor, in the lab, says to use a getline for this but i can't seem to make it work (visual studio doesn't recognize getline in this function)
#include <iostream>
#include <fstream>
#include "star.h"
#include <string>
using namespace std;
char getChoice();
void processSelection(char choice);
void processA();
(skipping crap you don't need)
static char filePath[ENTRY_SZ];
void processA() {
ifstream openFile;
long temp, test;
double lum, mass, rad;
char name;
cout << "Please enter the full file path" << endl;
cin >> filePath;
openFile.open(filePath, ios::in);
if (openFile.good() != true) {
cout << "this file path was invalid";
}
while (openFile.good())
{
star *n = new star;
// getline(openFile, name, ',');
star(name);
getline(openFile, temp, ',');
n->setTemperature(temp);
getline(openFile, lum, ',');
n->setLuminosity(lum);
getline(openFile, mass, ',');
n->setMass(mass);
cin >> rad;
n->setRadius(rad);
}
}
From what i'm reading online (including older posts) and what my CS tutor says this should work so any help will be appreciated.
The suggestion to use std::getline() is likely implying that you'd first read a std::string and then deal with the content of this std::string, e.g., using std::istringstream.
I'd suggest not to use std::getline() and, of course, to also check inputs after they are read. To deal with the comma separator after non-std::string fields I'd use a custom manipulator:
std::istream& comma(std::istream& in) {
if ((in >> std::ws).peek() == ',') {
in.ignore();
}
else {
in.setstate(std::ios_base::failbit);
}
return in;
}
This manipulator skips leading whitespace (using the manipulator std::ws) and then simply checks if the next character is a comma. If so, the comma is extracted, otherwise the stream is set into failure mode and further attempts to read will fail until the failure state is dealt with (e.g., by using in.clear() and probably getting rid of any offending characters).
With this manipulator it is easy to read the respective values. Note, that when switching from formatted to unformatted input it is likely necessary that leading whitespace (e.g., in this case line breaks) need to be ignored. Also, the code below first attempts to read the values and uses them only when this attempt was successful: input shall always be checked after a read attempt was made, not before!
// ...
long temp;
double lum, mass, rad;
std::string name;
while (std::getline(in >> std::ws, name, ',')
>> temp >> comma
>> lum >> comma
>> mass >> comma
>> rad) {
// use the thus read values
}
I am writing a program for my class that takes a text file and has each line in the text assigned.The problem i am having is that when i use the getline() its completely skipping the input. From everything i have read i feel like i am doing it right but obviously i am missing something.This is a small part of the code...if you need the whole thing i can post it.Thanks ahead of time for everyone's help.
garage populategarage()
{
garage tg; //temporary garage
string instruction_prompt;
initialize_garage(tg);
ifstream inputFile;
inputFile.open("garage-input-file.txt");
for (int i = 0; i < NUM_OF_VEHICLES; i++)
{
inputFile >> tg.vehicles[i].category;
if (tg.vehicles[i].category == "\0")
i = NUM_OF_VEHICLES;
else
{
inputFile >> tg.vehicles[i].make;
inputFile >> tg.vehicles[i].model;
inputFile >> tg.vehicles[i].color;
inputFile >> tg.vehicles[i].year;
inputFile >> tg.vehicles[i].trans;
inputFile >> tg.vehicles[i].cylinder;
getline(inputFile, tg.vehicles[i].drive); //This is my problem
}
}
You haven't shown any example input, or what your results are, but from your description it seems like each value appears on its own line. Would that be right? In that case, the getline call is likely to be picking up the previous newline (from when you read cylinder), and returning an empty string.
If your values appear on separate lines, you should probably use getline for each. You can wrap this behaviour for any type into a template function - something simple like:
template <class T>
istream & readValue( istream & s, T & value )
{
string line;
if( getline( s, line ) )
{
istringstream iss( line );
iss >> value;
}
return s;
}
If instead your file contains a single line for each entry, then it's usually better to use getline for the whole line, then read individual values from an istringstream.
for (int i = 0; i < NUM_OF_VEHICLES; i++)
{
string line;
if( !getline( inputFile, line ) ) break;
istringstream iss( line );
iss >> tg.vehicles[i].make;
iss >> tg.vehicles[i].model;
// etc...
}
I want to parse a file which describes a set of data line by line. Each datum consists of 3 or four parameters: int int float (optional) string.
I opened file as ifstream inFile and used it in a while loop
while (inFile) {
string line;
getline(inFile,line);
istringstream iss(line);
char strInput[256];
iss >> strInput;
int i = atoi(strInput);
iss >> strInput;
int j = atoi(strInput);
iss >> strInput;
float k = atoi(strInput);
iss >> strInput;
cout << i << j << k << strInput << endl;*/
}
The problem is that the last parameter is optional, so I'll probably run into errors when it is not present. How can i check in advance how many parameters are given for each datum?
Furthermore,
string line;
getline(inFile,line);
istringstream iss(line);
seems a bit reduldant, how could I simplyfiy it?
Use the idiomatic approach in this situation, and it becomes much simpler:
for (std::string line; getline(inFile, line); ) {
std::istringstream iss(line);
int i;
int j;
float k;
if (!(iss >> i >> j)) {
//Failed to extract the required elements
//This is an error
}
if (!(iss >> k)) {
//Failed to extract the optional element
//This is not an error -- you just don't have a third parameter
}
}
By the way, atoi has some highly undesired ambiguity unless 0 is not a possible value for the string you're parsing. Since atoi returns 0 when it errors, you cannot know if a return value of 0 is a successful parsing of a string with a value of 0, or if it's an error unless you do some rather laborious checking on the original string you had it parse.
Try to stick with streams, but in situations where you do need to fall back to atoi type functionality, go with the strtoX family of functions (strtoi, strtol, strtof, etc). Or, better yet, if you're using C++11, use the stoX family of functions.
You could use a string tokenizer How do I tokenize a string in C++?
In particular: https://stackoverflow.com/a/55680/2436175
Side note: you do not need to use atoi, you could simply do:
int i,j;
iss >> i >> j;
(but this wouldn't handle alone the problem of optional elements)
I'm new to C++ and I'm having a little trouble when it comes to reading lines of data from a text file. Let's say I have an unknown number of lines in a text file, with each line in the same format: int string double . The only thing that will be definite is a space will separate each piece of data on a given line. I'm using an array of structs to store the data. The code below works great except that it skips a line of input after each loop. I've tried inserting various ignore() statements and still can't get it to read each line, only every other line. If I rewrite some of the getline statements at the end, then the wrong data starts getting stored for the variables after the first loop.
Text file might look like this:
18 JIMMY 71.5
32 TOM 68.25
27 SARAH 61.4
//code
struct PersonInfo
{
int age;
string name;
double height;
};
//..... fstream inputFile; string input;
PersonInfo *people;
people = new PersonInfo[50];
int ix = 0;
getline(inputFile, input, ' ');
while(inputFile)
{
people[ix].age = atoi(input.c_str());
getline(inputFile, input, ' ');
people[ix].name = input;
getline(inputFile, input, ' ');
people[ix].height = atof(input.c_str());
ix++;
getline(inputFile, input, '\n');
getline(inputFile, input, ' ');
}
I'm sure there are more advanced ways to do this, but like I said I'm pretty new to C++ so if there are just some slight modifications to the code above, that would be great. Thanks!
You can do the file reading as follows:
int ix = 0;
int age = 0;
string name ="";
double height = 0.0;
ifstream inputFile.open(input.c_str()); //input is input file name
while (inputFile>> age >> name >> height)
{
PersonInfo p ={age, name, height};
people[ix++] = p;
}
You've made this whole code ridiculously complicated.
struct PersonInfo
{
int age;
string name;
double height;
};
std::vector<PersonInfo> people;
PersonInfo newPerson;
while(inputFile >> newPerson.age >> newPerson.name >> newPerson.height)
people.push_back(std::move(newPerson));
Your problem is because first your read each bit of data one at a time from the file, then a whole line from teh file, then each bit of data one at a time from the file again. Maybe what you intended was more like this?
std::string fullline;
while(std::getline(inputFile, fullline)) {
std::stringstream linestream(fullline);
std::getline(linestream, datawhatever);
....
}
By the way, more idiomatic code might look like more like this:
std::istream& operator>>(std::istream& inputFile, PersonInfo& newPerson)
{return inputFile >> newPerson.age >> newPerson.name >> newPerson.height;}
{ //inside a function
std::ifstream inputFile("filename.txt");
typedef std::istream_iterator<PersonInfo> iit;
std::vector<PersonInfo> people{iit(inputFile), iit()}; //read in
}
Proof it works here
I am having some trouble with my lab assignment for my CMPT class...
I am trying to read a text file that has two words and a string of numbers per line, and the file can be as long as anyone makes it.
An example is
Xiao Wang 135798642
Lucie Chan 122344566
Rich Morlan 123456789
Amir Khan 975312468
Pierre Guertin 533665789
Marie Tye 987654321
I have to make each line a separate "student", so I was thinking of using struct to do so, but I don't know how to do that as I need the first, last, and ID number to be separate.
struct Student{
string firstName;
string secondName;
string idNumber;
};
All of the tries done to read in each word separately have failed (ended up reading the whole line instead) and I am getting mildly frustrated.
With the help from #Sylence I have managed to read in each line separately. I am still confused with how to split the lines by the whitespace though. Is there a split function in ifstream?
Sylence, is 'parts' going to be an array? I saw you had indexes in []'s.
What exactly does the students.add( stud ) do?
My code so far is:
int getFileInfo()
{
Student stdnt;
ifstream stdntFile;
string fileName;
char buffer[256];
cout<<"Please enter the filename of the file";
cin>>filename;
stdntFile.open(fileName.c_str());
while(!stdFile.eof())
{
stdFile.getLine(buffer,100);
}
return 0;
}
This is my modified and final version of getFileInfo(), thank you Shahbaz, for the easy and quick way to read in the data.
void getFileInfo()
{
int failed=0;
ifstream fin;
string fileName;
vector<Student> students; // A place to store the list of students
Student s; // A place to store data of one student
cout<<"Please enter the filename of the student grades (ex. filename_1.txt)."<<endl;
do{
if(failed>=1)
cout<<"Please enter a correct filename."<<endl;
cin>>fileName;
fin.open(fileName.c_str());// Open the file
failed++;
}while(!fin.good());
while (fin >> s.firstName >> s.lastName >> s.stdNumber)
students.push_back(s);
fin.close();
cout<<students.max_size()<<endl<< students.size()<<endl<<students.capacity()<<endl;
return;
}
What I am confused about now is how to access the data that was inputted! I know it was put into a vector, but How to I go about accessing the individual spaces in the vector, and how exactly is the inputted data stored in the vector? If I try to cout a spot of the vector, I get an error because Visual Studio doesn't know what to output I guess..
The other answers are good, but they look a bit complicated. You can do it simply by:
vector<Student> students; // A place to store the list of students
Student s; // A place to store data of one student
ifstream fin("filename"); // Open the file
while (fin >> s.firstName >> s.secondName >> s.idNumber)
students.push_back(s);
Note that if istream fails, such as when the file finishes, the istream object (fin) will evaluate to false. Therefore while (fin >> ....) will stop when the file finishes.
P.S. Don't forget to check if the file is opened or not.
Define a stream reader for student:
std::istream& operator>>(std::istream& stream, Student& data)
{
std::string line;
std::getline(stream, line);
std::stringstream linestream(line);
linestream >> data.firstName >> data.secondName >> data.idNumber;
return stream;
}
Now you should be able to stream objects from any stream, including a file:
int main()
{
std::ifstream file("data");
Student student1;
file >> student1; // Read 1 student;
// Or Copy a file of students into a vector
std::vector<Student> studentVector;
std::copy(std::istream_iterator<Student>(file),
std::istream_iterator<Student>(),
std::back_inserter(studentVector)
);
}
Simply read a whole line and then split the string at the spaces and assign the values to an object of the struct.
pseudo code:
while( !eof )
line = readline()
parts = line.split( ' ' )
Student stud = new Student()
stud.firstName = parts[0]
stud.secondName = parts[1]
stud.idNumber = parts[2]
students.add( stud )
end while