I am reading in data to a struct array. the data is separated by possible blank lines which i must ignore. my code is not working im wondering why
struct Location
{
string state;
string city;
int zipcode;
}
and heres the reading in im getting trouble with.
while (!fin.eof() && size < 50)
{
getline (fin, location[size].state);
getline (fin, location[size].city);
fin >> location[size].zipcode;
if (location[size].empty()) //to ignore blank lines but its not working?
continue;
size++;
}
any ideas? could it be the compiler?
It looks like you are trying to check for an empty string but are unintentionally trying to call empty() on a Location.
Did you mean
if (location[size].state.empty() && location[size].city.empty())
continue;
Edit:
If you would like for your code example to work as is and you are able to modify struct Loaction you could do the following.
struct Location
{
std::string state;
std::string city;
int zipcode; //who cares about zip+4
Location():zipcode(0){};
bool empty()
{
return state.empty() && city.empty() && !zipcode;
}
};
Related
I'm looking for a way to find the number of items in a .txt file.
The file structure is as follows:
students.txt pricem 1441912123
house.pdf jatkins 1442000124
users.txt kevin_tomlinson 1442001032
accounts.mdb kevin_tomlinson 1442210121
vacation.jpg smitty83 1442300125
calendar.cpp burtons 1442588012
The result should be 18 in this example since there are 18 separate "words" in this file.
I need that value so I can iterate through the items and assign them to an array of structures (maybe there's a way to accomplish both of these steps together?):
// my structure
struct AccessRecord
{
string filename;
string username;
long timestamp;
};
// new instance of AccessRecord
// max possible records: 500
AccessRecord logRecords[500];
// while file has content
while (!fin.eof())
{
// loop through file until end
// max possible records: 500
for (int i = 0; i < 500; i++) // need to figure out how to iterate
{
fin >> logRecords[i].filename
>> logRecords[i].username
>> logRecords[i].timestamp;
}
}
Which will then be written to the screen.
So the question is, how do I find the count? Or is there a better way?
You know that each line contains a string, a string and a long, so you can iterate with:
std::vector<AccessRecord> logs;
std::string fname, uname;
long tstamp;
while(fin >> fname >> uname >> tstamp) {
logs.push_back(AccessRecord(fname, uname, tstamp));
//To avoid copies, use: (thanks #Rakete1111!)
//logs.emplace_back(std::move(fname), std::move(uname), tstamp);
}
This is assuming you've created a constructor for your struct like:
AccessRecord(std::string f, std::string u, long t)
: filename(f), username(u), timestamp(t) { }
Notice that I'm using an std::vector here instead of an array so that we don't even have to worry about the number of items, since the vector will resize itself dynamically!
You should overload operator>> for your structure:
struct AccessRecord
{
string filename;
string username;
long timestamp;
friend std::istream& operator>>(std::istream& input, AccessRecord& ar);
};
std::istream& operator>>(std::istream& input, AccessRecord& ar)
{
input >> ar.filename;
input >> ar.username;
input >> ar.timestamp;
return input;
}
This allows you to simplify your input function:
AccessRecord ar;
std::vector<AccessRecord> logs;
//...
while (fin >> ar)
{
database.push_back(ar);
}
Usually, if you are accessing an objects data members directly outside of the class or structure, something is wrong. Search the internet for "data hiding", "c++ encapsulation" and "c++ loose coupling".
I have an array of dvd from a Video class I created
Video dvd[10];
each video has the property,
class Video {
string _title;
string _genre;
int _available;
int _holds;
public:
Video(string title, string genre, int available, int holds);
Video();
void print();
void read(istream & is, Video dvd);
int holds();
void restock(int num);
string getTitle();
~Video();
};
I'm trying to fill up this array with data from my text file where each info such as the title and genre is separated by a comma
Legend of the seeker, Fantasy/Adventure, 3, 2
Mindy Project, Comedy, 10, 3
Orange is the new black, Drama/Comedy, 10, 9
I've tried using getline(in, line, ',') but my brain halts when its time to insert each line into the dvd array.
I also created a read method to read each word separated by a whitespace but I figured thats not what I really want.
I also tried to read a line with getline, store the line in a string and split it from there but I get confused along the line.
**I can get the strings I need from each line, my confusion is in how to insert it into my class array in the while loop especially when I can only read one word at a time.
I need help on what approach I should follow to tackle this problem.
**My code
#include <iostream>
#include <fstream>
#include <cassert>
#include <vector>
#define MAX 10
using namespace std;
class Video {
string _title;
string _genre;
int _available;
int _holds;
public:
Video(string title, string genre, int available, int holds);
Video();
void print();
void read(istream & is, Video dvd);
int holds();
void restock(int num);
string getTitle();
~Video();
};
Video::Video(string title, string genre, int available, int holds){
_title = title;
_genre = genre;
_available = available;
_holds = holds;
}
void Video::read (istream & is, Video dvd)
{
is >> _title >> _genre >> _available>>_holds;
dvd = Video(_title,_genre,_available,_holds);
}
int Video::holds(){
return _holds;
}
void Video::restock(int num){
_available += 5;
}
string Video::getTitle(){
return _title;
}
Video::Video(){
}
void Video::print(){
cout<<"Video title: " <<_title<<"\n"<<
"Genre: "<<_genre<<"\n"<<
"Available: " <<_available<<"\n"<<
"Holds: " <<_holds<<endl;
}
Video::~Video(){
cout<<"DESTRUCTOR ACTIVATED"<<endl;
}
int main(int params, char **argv){
string line;
int index = 0;
vector<string> tokens;
//Video dvd = Video("23 Jump Street", "comedy", 10, 3);
//dvd.print();
Video dvd[MAX];
dvd[0].holds();
ifstream in("input.txt");
/*while (getline(in, line, ',')) {
tokens.push_back(line);
}
for (int i = 0; i < 40; ++i)
{
cout<<tokens[i]<<endl;
}*/
if(!in.fail()){
while (getline(in, line)) {
dvd[index].read(in, dvd[index]);
/*cout<<line<<endl;
token = line;
while (getline(line, token, ',')){
}
cout<<"LINE CUT#####"<<endl;
cout<<line<<endl;
cout<<"TOKEN CUT#####"<<endl;*/
//dvd[index] =
index++;
}
}else{
cout<<"Invalid file"<<endl;
}
for (int i = 0; i < MAX; ++i)
{
dvd[i].print();
}
}
First, I would change the Video::read function into an overload of operator >>. This will allow the Video class to be used as simply as any other type when an input stream is being used.
Also, the way you implemented read as a non-static member function returning a void is not intuitive and very clunky to use. How would you write the loop, and at the same time detect that you've reached the end of file (imagine if there are only 3 items to read -- how would you know to not try to read a fourth item)? The better, intuitive, and frankly, de-facto way to do this in C++ is to overload the >> operator.
(At the end, I show how to write a read function that uses the overloaded >>)
class Video
{
//...
public:
friend std::istream& operator >> (std::istream& is, Video& vid);
//..
};
I won't go over why this should be a friend function, as that can be easily researched here on how to overload >>.
So we need to implement this function. Here is an implementation that reads in a single line, and copies the information to the passed-in vid:
std::istream& operator >> (std::istream& is, Video& vid)
{
std::string line;
std::string theTitle, theGenre, theAvail, theHolds;
// First, we read the entire line
if (std::getline(is, line))
{
// Now we copy the line into a string stream and break
// down the individual items
std::istringstream iss(line);
// first item is the title, genre, available, and holds
std::getline(iss, theTitle, ',');
std::getline(iss, theGenre, ',');
std::getline(iss, theAvail, ',');
std::getline(iss, theHolds, ',');
// now we can create a Video and copy it to vid
vid = Video(theTitle, theGenre,
std::stoi(theAvail), // need to change to integer
std::stoi(theHolds)); // same here
}
return is; // return the input stream
}
Note how vid is a reference parameter, not passed by value. Your read function, if you were to keep it, would need to make the same change.
What we did above is that we read the entire line in first using the "outer" call to std::getline. Once we have the line as a string, we break down that string by using an std::istringstream and delimiting each item on the comma using an "inner" set of getline calls that works on the istringstream. Then we simply create a temporary Video from the information we retrieved from the istringstream and copy it to vid.
Here is a main function that now reads into a maximum of 10 items:
int main()
{
Video dvd[10];
int i = 0;
while (i < 10 && std::cin >> dvd[i])
{
dvd[i].print();
++i;
}
}
So if you look at the loop, all we did is 1) make sure we don't go over 10 items, and 2) just use cin >> dvd[i], which looks just like your everyday usage of >> when inputting an item. This is the magic of the overloaded >> for Video.
Here is a live example, using your data.
If you plan to keep the read function, then it would be easier if you changed the return type to bool that returns true if the item was read or false otherwise, and just calls the operator >>.
Here is an example:
bool Video::read(std::istream & is, Video& dvd)
{
if (is.good())
{
is >> dvd;
return true;
}
return false;
}
And here is the main function:
int main()
{
Video dvd[10];
int i = 0;
while (i < 10 && dvd[i].read(std::cin, dvd[i]))
{
dvd[i].print();
++i;
}
}
Live Example #2
However, I still say that the making of Video::read a non-static member makes the code in main clunky.
I'm practicing C++ and have made a class that stores sequences read in from fast format as well as their names. The code is below:
#include<fstream>
#include<iostream>
#include<string>
#include<vector>
using namespace std;
class Sequence {
vector<string> fullSequence, sequenceNames;
public:
void fastaRead(string fileName);
string getSequence(int index);
};
string Sequence::getSequence(int index)
{
return fullSequence[index];
}
void Sequence::fastaRead(string fileName)
{
vector<string> fullSequence, sequenceNames;
ifstream inputFile;
inputFile.open(fileName);
if (inputFile.is_open()) {
string currentSeq;
string line;
bool newseq = false;
while (getline(inputFile, line))
{
if (line[0] == '>') {
sequenceNames.push_back(line.substr(1,line.size()));
newseq = true;
} else {
if (newseq == true) {
fullSequence.push_back(currentSeq);
currentSeq = line;
newseq = false;
} else {
currentSeq.append(line);
}
}
}
}
inputFile.close();
}
int main()
{
Sequence inseq;
cout << "Fasta Sequence Filepath" << endl;
string input;
getline(cin, input);
inseq.fastaRead(input);
inseq.getSequence(0);
return 0;
}
However when I run the program with the following dummy input file:
>FirstSeq
AAAAAAAAAAAAAA
BBBBBBBBBBBBBB
>SecondSeq
TTTTTTTTTTTTTT
>ThirdSequence
CCCCCCCCCCCCCC
>FourthSequence
GGGGGGGGGGGGGG
I get a segmentation fault when the line inset.getSequence(0) is called. What is it I've done that causes the seg fault and how do I make sure it doesn't happen? I know it can have something to do with errors in pointers, but I don't think I've used pointers which if I remember correctly requires the * character.
Thanks,
Ben.
You need to remove vector<string> fullSequence, sequenceNames; in the void Sequence::fastaRead function. When you define those variables inside that function and use them, you are not accessing the ones in the class that have the same name, you are accessing the local variables that you have defined in that function, unless you prepend them with this-> while accessing.
The variables in the class are actually empty and you get a segmentation fault.
I am making a file reading class. It should, when constructed open the file with the given string and depending on which constructor is called use the second string supplied to skip through the file to the line after the string given.
Here is my code as it stands:
SnakeFileReader::SnakeFileReader(string filePath)
{
fileToRead_.open(filePath.c_str(), ios::in);
}
SnakeFileReader::SnakeFileReader(string filePath, string startString)
{
fileToRead_.open(filePath.c_str(), ios::in);
string toFind;
while (toFind != startString && !fileToRead_.eof())
{
fileToRead_ >> toFind;
}
}
string SnakeFileReader::ReadLine()
{
string fileLine;
if (!fileToRead_.fail() && !fileToRead_.eof())
fileToRead_ >> fileLine;
return fileLine;
}
int SnakeFileReader::ReadInt()
{
string fileLine = "";
if (!fileToRead_.fail() && !fileToRead_.eof())
fileToRead_ >> fileLine;
int ret;
istringstream(fileLine) >> ret;
return ret;
}
SnakeFileReader::~SnakeFileReader()
{
fileToRead_.close();
}
The problem I have is that in the second constructor I get a segmentation fault. I get another segmentation fault in the read line function as soon as I declare a string.
[Edit] Here is the extra code requested. I am making a "Snake Game" as a part of the first year of my degree. I want the game to read and save files rather than hard code variable values. I will finally be using this class a lot to setup a level in the game. However here are a few lines that should demonstrate how i intend to use this class:
//Level.cpp
std::string fileToRead = "resources/files/level1.txt";
SnakeFileReader sfr(fileToRead);
std::string mapFilePath = sfr.ReadLine();
ImageFile(mapFilePath).load(map_layout);
mapWidth_ = sfr.ReadInt();
mapHeight_ = sfr.ReadInt();
level_cell_size_ = sfr.ReadInt();
map_ = new TileData*[mapWidth_];
for (int i = 0; i < mapWidth_; i++)
{
map_[i] = new TileData[mapHeight_];
}
Layout of the file:
resources/images/Map1_Layout.bmp
40
30
20
Class declaration:
#ifndef SNAKE_FILE_READER_HPP
#define SNAKE_FILE_READER_HPP
#include <iostream>
#include <fstream>
#include <sstream>
using namespace std;
class SnakeFileReader
{
public:
SnakeFileReader(string filePath);
SnakeFileReader(string filePath, string startString);
~SnakeFileReader();
string ReadLine();
int ReadInt();
private:
ifstream fileToRead_;
};
#endif // SNAKE_FILE_READER_HPP
in the ReadLine function, you return a reference to a variable allocated on the functions stack. you are corrupting the stack, crazy things can happen. your compiler should have warned you about that.
I'm not sure about your constructor, but the problem with ReadLine() is that you're trying to return the memory address of an automatic variable, which is destroyed when you exit the function.
The simplest fix would be to remove the '&' on the return value, and just return a string. But if you're determined to return a memory address, try this instead:
string *SnakeFileReader::ReadLine()
{
string *fileLine = new string;
if (!fileToRead_.fail() && !fileToRead_.eof())
fileToRead_ >> *fileLine;
return fileLine;
}
This will dynamically allocate the string and pass back the pointer. The difference is that dynamic variables are not automatically destroyed when you leave their scope. The string will still exist on the heap until you delete it yourself (which you must remember to do when you're done with it).
I am trying to read the lines from a file called 'weapon.txt' and input them into a structure something a long the lines of this
struct weapon
{
char name[20]; //Edited
int strength;
}
The file to be read looks like this:
Excalibur
150
Throwing Stars
15
Rapier
200
Bow and Arrow
100
Axe
200
Crossbow
100
Scimitar
250
Rusted Sword
10
Soul Slayer
500
The code I have right now is
#include<fstream>
#include<iostream>
#include<cstring>
using namespace std;
struct WeaponInfo
{
char name[16];
int strength;
};
const int MaxWeap = 10;
void openfile(ifstream&); //Opening the file
void displayfile(ifstream&, WeaponInfo&);//Display file
int main ()
{
WeaponInfo weapon[MaxWeap];
ifstream fin;
openfile(fin);
displayfile(fin, weapon[MaxWeap]);
}
void openfile(ifstream& fin)
{
fin.open("weapon.txt");
}
void displayfile(ifstream& fin, WeaponInfo& weapon[MaxWeap])
{
char nm;
int str;
while (fin.eof() == 0)
{
for(int i = 0; i <= MaxWeap; i++);
{
fin.getline(nm);
fin.getline(str);
strcpy(weapon[i].name, nm);
strcpy(weapon[i].strength, str);
i++;
cout << weapon[i].name << "\n" << weapon[i].strength << endl;
}
}
fin.close();
}
EDIT: This is what I have right now after re-doing it, I am getting compile errors of : declaration of 'weapon' as array of references; In function 'void displayfile(...) 'fin' was not declared in this scope; 'weapon' is not declared in this scope; ma,e lookup of 'i' changed for ISO 'for' scoping [-fpermissive].
I'd firstly tend to use std::string rather than char arrays - they're just easier to work with. So the structure noww looks like this:
struct weapon
{
string name;
int strength;
};
Next you need something that will read the structure from an input stream:
bool getWeapon( ifstream& is, weapon& w )
{
getline(is, w.name) ;
string strengthStr;
getline(is, strengthStr) ;
w.strength = strtol( strengthStr.c_str(), NULL, 0 );
return !is.eof();
}
Two things here, I've used strtol as a conversion function from string to int. atoi is used but strtol gives you slightly more flexibility and crucially, better error cchecking, alkthough I've not bothered to implement it here. A stringstream might have been another alternative here.
Secondly, I return a boolean indicating whether the name was empty. The reason for this is that when, later in the code, I check for eof() on the ifstream, it isn't actually set until you read past the end of the file. So the last good read will not set it but the first attempt to reead past it will. Returning false here then will indicate to the caller that the 'get' failed due to the ifstream being at end of file.
Lastly, we need something to read all of the weappons in:
ifstream input;
input.open("weapons.txt");
vector<weapon> ws;
if ( input )
{
while (! (input.eof()))
{
weapon w;
if ( ! getWeapon( input, w ) )
break;
ws.push_back( w );
}
}
input.close();
This wwill place all the weapons into a vector. Note the call to getWeapon breaks if it failed to prrevent adding on an 'empty' weapon. Not the most glamorous solution but it should work.
Pseudo-code goes something like this, (and like Martol1ni has coded for you):
open the file
while (!end-of file)
{
create instance of struct weapon
read a line and strcpy into weapon.name
read a line and set weapon.strength = atoi(line)
do something with the instance, eg. add to list, call a member function, etc.
}
loop
close file.
Assuming you control the weapons.txt, don't bother checking for errors in the file, you can do this. Next time, do a little research... :)
#include <fstream>
#include <vector>
#include <string>
#include <iostream>
#include <cstdlib>
using namespace std;
struct weapon
{
string name;
int strength;
weapon(string n, int s) : name(n), strength(s) {}
};
void readFileToVec(vector<weapon> &myVec) {
ifstream in("weapon.txt");
while (!in.eof()) {
string name;
getline(in,name);
string strength;
getline(in,strength);
weapon myWep(name,atoi(strength.c_str()));
myVec.push_back(myWep);
}
in.close();
}