I am trying to use dynamic memory for this project. I am getting a seg fault but I cannot figure out what I am doing incorrectly. Can anyone point to where my mistake is? The file seems to read in correctly...but im assuming the fault is a rogue pointer..help!
I am just trying to read in "heart two 2" to "spade ace 11" in from a file, all words seperated by a space. my program worked before using dynamic memory..
#include <iostream>
#include <fstream>
#include <ctime>
#include <stdlib.h>
#include <string>
using namespace std;
//global constant(s)
const int maxCards = 52;
//Structs
struct card
{
char *suit;
char *rank;
int cvalue;
char location;
};
void readDeck(card* deckPtr);
void cardsInit(char *finNameP,card *deckPtr);
//program
int main()
{
card *deckPtr = new card[52];
char *finNameP = new char[13];
strcopy(finNameP,"cardFile.txt");
cardsInit(finNameP,deckPtr); // function i wrote that works
readDeck(deckPtr); //simply reads the deck from &deckPtr[0] -> &deck[51]
delete [] finNameP;
}
void cardsInit(char *finNameP, card *deckPtr)
{
//set up card file to be read in
ifstream fin;
cout << "Please enter file name...(cardFile.txt)" << endl;;
cin >> *finNameP;
fin.open(finNameP);
//create pointer and set initial value
card *deckHome = deckPtr;
for(int i=0;i<52;i++)
{
(*deckPtr).suit = new char[9];
(*deckPtr).rank = new char[9];
deckPtr++;
}
deckPtr = deckHome;
//check if cardFile.txt opens correctly
if(!fin.good())
{
cout << "Error with card file" << endl;
}
else
{
while(fin.good())
{
for(deckPtr = &deckPtr[0]; deckPtr < &deckPtr[maxCards];deckPtr++)
{
fin >> (*deckPtr).suit;
fin >> (*deckPtr).rank;
fin >> (*deckPtr).cvalue;
}
}
}
fin.close();
delete []finNameP;
delete [] (*deckPtr).suit;
delete [] (*deckPtr).rank;
}
This is a really ancient way to program. Instead of using new, use std::string or std::vector<char>. Those also use dynamic memory but they make it much harder for you to accidentally cause memory allocation bugs.
The first problem comes here:
cin >> *finNameP;
Since finNameP has type char *, then *finNameP has type char. So this instruction reads a single character. Then you go onto do fin.open(finNameP); which causes undefined behaviour because there is no string in finNameP.
The simplest fix is to make finNameP be a std::string. Note that doing cin >> finNameP (without changing the type) would compile, however it is a bad idea because there is no buffer overflow protection. You could write cin >> setw(12) >> finNameP; but that is still substantially worse than using a string.
deckPtr < &deckPtr[maxCards] is always true, the for loop runs forever.
Related
I am trying to get a few lines from a text file to store into a class, Item, and using vectors. However, when I read from the file into the program, nothing is stored.
Here is my main:
#include <vector>
#include <fstream>
#include <iostream>
#include "Item.h"
using namespace std;
void readFile(vector<Item>&);
int main()
{
vector<Item> items;
readFile(items);
int size = items.size();
for (int index = 0; index < size; index++)
{
cout << items[index].getName() << endl;
}
}
This is the function in question:
void readFile(vector<Item>& vecItems, int lines)
{
ifstream inventory;
inventory.open("inventory.txt");
string itemName;
int itemDept, itemPrice, itemQuan, itemShort, itemSurplus;
string line;
if (inventory.fail())
{
cout << "ERROR NO FILE FOUND (inventory.txt)\n";
exit(1);
}
while (inventory >> itemName >> itemDept >> itemPrice >> itemQuan >> itemShort >> itemSurplus)
{
Item temp(itemName, itemDept, itemPrice, itemQuan, itemShort, itemSurplus);
vecItems.push_back(temp);
}
inventory.close();
}
I've tried calling
temp.setName(itemName)
etc etc
individually but it still does not hold in the vector. Nothing outputs in main and the debugger says size = 0. Any help is appreciated
EDIT: This is the file format
vitamins 1 15.99 1105 500 1000
shampoo 2 6.99 298 300 500
Your problem is you have a bad read. item_price is declared as an int but the price in the file is a floating point number. When you try to read in item_price it capture everything up to the . and then stops reading. On the next read operation for itemQuan it gets the . and fails as . is not a valid int. Since the read fails you never enter the while loop body which means you never create any objects.
Change item_price to a float, double or std::string to fix this.
Code:
#include<iostream.h>
#include<fstream.h>
#include<string.h>
int n = 0, flag = 0,i;
struct bac
{
char name[10];
char amt[5];
} s;
void main()
{
ofstream f("C:\\TC\\1.dat");
for(i=0;i<10;i++)
{
cout << "\nenter the details ";
cin >> s.name >> s.amt;
f.write((char *)&s, sizeof(bac));
}
}
sometimes the code works fine
but at the other times , when i look at the output file,it is empty , the problem has come up many times , and i ant to know whether there is a precaution regarding loops with file handling
for eg. in other program
.....
while(ch!=4)
{
cout << "\nBANK MANAGEMENT SYSTEM \n";
cout << "enter choice ";
cout << "\n1.add\n2.search\n3.delete and overwrite ";
cin >> ch;
if (ch == 1)
{
cout << "\nenter the details ";
cin >> s.name >> s.amt;
f.write((char *)&s, sizeof(bac));
}
.....
the file is empty
I guess you may have used a very old compiler older than gcc 4.5.3.
I tried your code and it has no problem.
#include <iostream> //use header file without using deprecated iostream.h
#include <fstream> //same reason as above
#include <string>
using namespace std;
int n = 0, flag = 0,i;
struct bac
{
char name[10];
char amt[5];
} s;
int main() //usually main returns int. void was kind of old now
{
ofstream f("test.txt");
for(i=0;i<10;i++)
{
cout << "\nenter the details ";
cin >> s.name >> s.amt;
f.write((char *)&s, sizeof(bac));
}
f.flush();
f.close();
return 0;
}
I compiled the code in gcc 4.5.3 and ran it. the file has all the stuff I entered.
However, it will be better to use the << operator when you use file i/o stream to write to file.
You can find more information about and from top of this link:
http://members.gamedev.net/sicrane/articles/iostream.html
Another point, wen you have done writing to a file, remember to flush and close the file handle, otherwise, sometimes it will cause some annoying problems.
The code doesn't seem very C++-like to me...
To answer the last question, there aren't any gotchas about fstreams in loops specifically, no.
I suggest first trying to do f.write with the members name and amt themselves—compilers might add padding between name and amt, creating unwanted garbage output.
Are you sure you have write permission to the filepath all the time? Try opening a local file, as in the path being simply "1.dat".
Also try opening the file as f("/* file name */", ofstream::out | ofstream::app). "out" sets it as an output stream, and "app" makes it add to the end of the file. www.cplusplus.com/ofstream details more flags.
since you are using c++, I suggest you use a formal way to use ofstream, in your code, it should be f << s.name << s.amt.
remember, you are using c++, so keep using i/o stream.
I am working on a small program that takes a input file and processors the data in the file. With my current code (see below) when you enter a valid file name it just freezes the command line (drops down a line and just shows a flashing _ ) and I have to kill the program to get out. If you enter a invalid file name the if(!file) gets called and runs fine.
Whats really odd is that if I put a debugging cout above that if statement it will not get called if the file name is correct. Hope you can help and if you need more info let me know!
This is my current code:
using namespace std;
#include <iostream>
#include <stdexcept>
#include <string>
#include <fstream>
#include <vector>
#include <cctype>
#include "Student.h"
int main(){
string filename, name;
char *inputfile;
ifstream file;
vector<Student> students;
const int SIZE = 200;
char buffer [SIZE];
int regno, i;
cout << "Enter file name: ";
cin >> filename;
inputfile = const_cast<char*> (filename.c_str());
file.open(inputfile);
if (!file){
cout << "Failed to open " << filename << endl;
exit(1);
}
while (!file.eof()){
file.getline(buffer, SIZE);
i = 0;
regno = 0;
while (isdigit(buffer[i])){
regno = (regno*10)+buffer[i];
}
cout << regno;
}
file.close();
}
Your problems is that you never increase i in the cycle.
Here:
i = 0;
regno = 0;
while (isdigit(buffer[i])){
regno = (regno*10)+buffer[i];
}
You go into infinite cycle as i always stays 0.
Also why do you do the const_cast? You can open using a const char * too. So you can write this:
cin >> filename;
file.open(filename.c_str());
And code will still work.
There's another problem in your code concerning the use of getline() and eof(). The idiomatic way to read a file line-by-line is this:
std::string line;
while(getline(in, line)) {
// handle line here
}
in refers to some input stream like a std::ifstream or std::cin. The point is that reading a line can fail (e.g. due to EOF), which you check in above loop. Your version only checks if EOF was encountered before but not that the subsequent getline() call actually yielded any data.
Ok so I'm doing a program for class when I run across a bug I've never seen before and no idea what to do about it with only minimal experience with using the debugger, so I've come here hoping someone here can set me down the path to fixing this bug. My bug is the access violation reading location. Here is the portion of code that seems to be giving me the error:
#include "Book.h"
using namespace std;
void add (char*, char*, int);
void remove (int&);
void list ();
int Count;
Book Bookshelf [4];
int main ()
{
char* In = "";
char* N = "";
char* A = "";
int Y;
int Num;
do
{
cout << "Bookshelf> ";
cin >> In;
if (In == "add")
{
cout << "Bookshelf> Enter book: ";
cin >> N >> A >> Y;
add (N,A,Y);
}
else if (In == "remove")
{
cout << "Bookshelf> Select number: ";
cin >> Num;
remove (Num);
}
else if (In == "list")
{
}
} while (cin != "quit");
return 0;
}
void add (char* N, char* A, int Y)
{
if (Bookshelf[4].IsEmpty() == false)
cout << "Error!" << endl;
else
{
Bookshelf[Count] = Book (N,A,Y);
Count++;
}
cout << "Bookshelf> ";
}
I get the error when I type add into the command line to try to call the add function but it happens immediately so the debugger is no help to me. I know the problem is probably really simple but I can't seem to find it. Any help you can offer would be greatly appreciated. Let me know if any more code samples are needed.
You shouldn't use char* unless you really know what you are doing. For example, I rarely use char* at all and I'm programming with C++ since about 20 years. You want to use std::string, e.g. like this:
std::string In;
if (std::cin >> In) { ... }
The reason your code doesn't work is that the input operator wants to store data at the location pointed to by your pointer. However, this pointer is pointing at immutable memory for a c-string literal. When the operator tries to store something at this location it immediately gets an access violation.
The easiest fix is to use std::string. If you can't use std::string for whatever reason, use a preallocated array of char. If you do this, make sure you tell the stream how much characters are available by setting up the width:
char In[16];
if (std::cin >> std::setw(sizeof(In)) >> In) { ... }
(the reason I'm always using a check in these example is that it is very important that you always check whether your input was successful before you do anything with the result).
You cannot write data into space allocated for C-string literals: they are constants.
This is the part that leads to this behavior:
char* In = "";
cin >> In;
Two things are wrong:
Your variable In does not have enough space for any non-empty string.
Even if it did, writing to that space would not be allowed.
To fix this issue you could either (1) switch to using std::string (recommended) or (2) change declarations of your C strings to character arrays, like this:
char In[128];
This is a very strange issue. I'm trying to print a large text file, it's a Wikipedia entry. It happens to be the page on Velocity. So, when I tell it to print the file, it prints "In", when it should print "In physics, velocity is etc, etc etc".
Here's the code I'm using to print out:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
ifstream wiki;
wiki.open("./wiki/velocity.txt");
char* wikiRead;
wiki >> wikiRead;
cout << wikiRead << endl;
wiki.close();
}
Please help.
wiki >> wikiRead;
The default delimiter for stream is space, so when the stream encounters a space, it simply stops reading, that is why it reads only one word.
If you want the stream to read all words, the you've to use a loop as:
char* wikiRead = new char[1024]; //must allocate some memory!
while(wiki >> wikiRead)
{
cout << wikiRead << endl;
}
wiki.close();
delete []wikiRead; //must deallocate the memory
This will print all the words in the file, each on a new line. Note if any of the word in the file is more than 1024 character long, then this program would invoke undefined behavior, and the program might crash. In that case, you've to allocate a bigger chunk of memory.
But why use char* in the first place? In C++, you've better choice: Use std::string.
#include<string>
std::string word;
while(wiki >> word)
{
cout << word << endl;
}
wiki.close();
Its better now.
If you want to read line-by-line, instead of word-by-word, then use std::getline as:
std::string line;
while(std::getline(wiki, line))
{
cout << line << endl;
}
wiki.close();
This will read a complete line, even if the line contains spaces between the words, and will print each line a newline.
You ask the stream to read the (binary) value of a pointer (probably 4 bytes, depending on your machine architecture), then you ask it to print the text pointed to by those 4 bytes!
I wonder why you ignored the compiler warning (most of the modern compiler warns you about using uninitialized variables). How about this?
ifstream wiki;
wiki.open("./wiki/velocity.txt");
char wikiRead[255];
wiki >> wikiRead;
cout << wikiRead << endl;
wiki.close();
Alternatively I'd suggest you to use string object with getline to get a single line of text.
string str;
getline(wiki, str);
The >> operator applied to a char * reads only one word. Moreover, you're reading into an uninitialized pointer, which is not valid. Usually std::string, not char *, is used for string processing in C++.
If you only want to print the file's contents, you can hook the file's buffer directly to std::cout:
int main() {
std::ifstream wiki("./wiki/velocity.txt");
std::cout << wiki.rdbuf() << '\n';
}
If you want to put the contents into an automatically-allocated string, use std::getline with the delimiter disabled.
int main() {
std::ifstream wiki("./wiki/velocity.txt");
std::string wiki_contents;
getline( wiki, wiki_contents, '\0' /* do not stop at newline */ );
std::cout << wiki_contents << '\n'; // do something with the string
}
Since you want to read a large file, reading it block by block is a better way.
ifstream wiki;
wiki.open("./wiki/velocity.txt");
const int buf_size = 1024;
char* wikiRead = 0;
int cnt = 1;
do
{
wikiRead = realloc( wikiRead, bufsize*cnt );
wiki.Read( wikiRead + (bufSize*(cnt-1)), buf_size ); //appends to reallocated memory
cnt++;
}while( !wiki.eof())
wikiRead[(bufSize*(cnt-2)) + wiki.gcount() + 1] = '\0'; // null termination.
wiki.Close();
cout << wikiRead;
delete[] wikiRead;
The operator>> is designed to only read one word at a time. If you want to read lines, use getline.
#include <iostream>
#include <fstream>
#include<string>
using namespace std;
int main()
{
ifstream wiki;
wiki.open("./wiki/velocity.txt");
string wikiRead;
while (getline(wiki, wikiRead))
{
cout << wikiRead << endl;
}
wiki.close();
}