the pseudocode for this assignment is essentually:
1. Open the specified file in binary mode
2. Save the file name in the fileNames array.
3. Determine the file size using seekg and tellg
4. Read the file contents into the character array in one statement
5. Close the file
6. Loop through the array, one character at a time and accumulate the sum of each byte
7. Store the sum into the checkSums array.
#include <iostream>
#include <string>
#include <iomanip>
#include <fstream>
#include <cstring>
using namespace std;
int main()
{
//declare variables
string filePath;
void savefile();
char choice;
int i, a, b, sum;
sum = 0;
a = 0;
b = 0;
ifstream inFile;
//arrays
const int SUM_ARR_SZ = 100;
string fileNames[SUM_ARR_SZ];
unsigned int checkSums[SUM_ARR_SZ];
do {
cout << "Please select: " << endl;
cout << " A) Compute checksum of specified file" << endl;
cout << " B) Verify integrity of specified file" << endl;
cout << " Q) Quit" << endl;
cin >> choice;
if (choice == 'a' || choice == 'A')
{
//open file in binary mode
cout << "Specify the file path: " << endl;
cin >> filePath;
inFile.open(filePath.c_str(), ios::binary);
//save file name
fileNames[a] = filePath;
a++;
//use seekg and tellg to determine file size
char Arr[100000];
inFile.seekg(0, ios_base::end);
int fileLen = inFile.tellg();
inFile.seekg(0, ios_base::beg);
inFile.read(Arr, fileLen);
inFile.close();
for (i = 0; i < 100000; i++)
{
sum += Arr[i];
}
//store the sum into checkSums array
checkSums[b] = sum;
b++;
cout << " File checksum = " << sum << endl;
}
if (choice == 'b' || choice == 'B')
{
cout << "Specify the file path: " << endl;
cin >> filePath;
if (strcmp(filePath.c_str(), fileNames[a].c_str()) == 0)
{
}
}
} while (choice != 'q' && choice != 'Q');
system("pause");
}
I'm getting values like "-540000" and I'm not sure how to fix this. Any help is greatly appreciated!
You're creating an array on the stack without zeroing its contents, so Arr will contain "garbage" data.
You're creating the buffer with a fixed size, which means you're wasting space if the file is smaller than 100,000 bytes and you can't process a file that's larger than 100,000 bytes (without reusing the buffer)
You iterate over every byte in the buffer instead of those bytes that represent the file if it's smaller than 100,000 bytes.
I also note you're mixing C and C++ string functions. You don't need to call C's strcmp if you're using string then use string::compare.
C++ does not require forward-declaration of local variables, your code would be cleaner if you only declared local variables when they're used, instead of all-at-once.
Related
I am writing a code that reads an input file of numbers, sorts them in ascending order, and prints them to output. The only thing printed to output is some really freaky symbols.
Here is my code
#include <fstream>
#include <iostream>
using namespace std;
int main()
{
int i, y, temp, num[20];
char file_nameI[21], file_nameO[21];
ofstream outfile;
ifstream infile;
cout << "Please enter name of input file: ";
cin >> file_nameI;
infile.open(file_nameI);
if (!infile)
{
cout << "Could not open input file \n";
return 0;
}
cout << "Please enter name of output file: ";
cin >> file_nameO;
outfile.open(file_nameO);
if (!outfile)
{
cout << "Could not open output file \n";
return 0;
}
for (i = 0; i < 20; i++)
{
y = i + 1;
while (y < 5)
{
if (num[i] > num[y]) //Correction3
{
infile >> temp;
temp = num[i];
num[i] = num[y];
num[y] = temp;
//y++; //Correction4
}
y++;
}
}
for (i = 0; i < 5; i++)
outfile << "num[i]:" << num[i] << "\n";
return 0;
}
Here is my input
6 7 9 0 40
Here is the output
„Ô,üþ 54
H|À°ÀzY „Ô,üþ 0
Problems with your code are already mentioned in the comments but again:
First problem is uninitialized elements of num[20] - elements of num have indeterminate values so accessing any of them triggers undefined behavior. You should first read them from the file or at least initialize them to some default value.
The part of code that should most likely do the sorting is just completely wrong. If you'd like to implement your own function for sorting, you can pick up some well-known algorithm like e.g. quicksort - but C++ Standard Library already provides sorting function - std::sort.
Besides obvious mistakes:
You are using char[] - in C++ it's almost always better to use std::string.
Your static array can only store 20 values and you are reading those from a file. You can use std::vector which can grow when you add more elements than its current capacity. It also automatically fixes the problem with uninitialized elements of num[20].
As mentioned in the comments you can organize your code and improve readability by splitting it into functions.
Here you've got it quickly rewritten. This code uses std::string instead of char[], std::vector to store the numbers and std::sort. If there is something you don't understand here, read SO documentation:
#include <fstream>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
vector<int> read_file(ifstream& in_file)
{
vector<int> vec;
int value;
while (in_file >> value)
{
vec.push_back(value);
}
return vec;
}
void write_file(ofstream& out_file, const vector<int>& values)
{
for (size_t i = 0; i < values.size(); ++i)
out_file << "value #" << i << ": " << values[i] << '\n';
}
int main()
{
string input_filename, output_filename;
ofstream out_file;
ifstream in_file;
cout << "Please enter name of input file: ";
cin >> input_filename;
in_file.open(input_filename);
if (!in_file)
{
cout << "Could not open input file\n";
return 0;
}
cout << "Please enter name of output file: ";
cin >> output_filename;
out_file.open(output_filename);
if (!out_file)
{
cout << "Could not open output file\n";
return 0;
}
auto numbers = read_file(in_file);
sort(begin(numbers), end(numbers));
write_file(out_file, numbers);
return 0;
}
You might forgot to store values in num array. Just update your code as follows and it will work.
infile.open(file_nameI);
if (!infile){
cout << "Could not open input file \n";
return 0;
} else{
i = 0;
while (infile >> num[i]){
i++;
}
}
I have been having some problems with my code. I was asked to input elements from an .dat file into an array. For class we have to do this for various files without knowing how many elements will be in each file. The only thing we know is that here will never be more then 5000 elements per file.
One of my input file has the following elements:
5.675207 -0.571210
0.728926 0.666069
2.290909 0.751731 2.004545 0.907396
0.702893 0.646427 5.909504 -0.365045
2.082645 0.871841 5.597107 -0.633507
6.117769 -0.164663 6.091736 -0.190282
5.571074 -0.653433 4.503719 -0.978307
3.983058 -0.745620
3.670661 -0.504729
5.857438 -0.413001
When I run my code:
#define _CRT_NONSTDC_NO_DEPRECATE
#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;
int main(int argc, char * argv[])
{
ifstream fin;
ofstream fout;
if (argc < 3)
{
cout << "Incorrect usage: prog.exe filenname number" << endl;
cout << "Exiting now, please try again." << endl;
return -1;
}
fin.open(argv[1]);
if (!fin)
{
cout << "Error opening file \"" << argv[1] << "\", exiting." << endl;
return -1;
}
fout.open(argv[2]);
int count = 0;
int word;
double points[5000];
while (fin >> word)
{
fin >> points[count];
++count;
}
fout << "Numer of points is: " << count/2 << endl;
for (int i = 0; i < count; i++)
{
fout << points[i] << " ";
}
fin.close();
fout.close();
return 0;
}
I outputted the elements just to make sure that they were properly inputted. I get the following and I don't know why.
0.675207 0.57121
0.728926 0.666069
0.290909 0.751731 0.004545 0.907396
0.702893 0.646427 0.909504 0.365045
0.082645 0.871841 0.597107 0.633507
0.117769 0.164663 0.091736 0.190282
0.571074 0.653433 0.503719 0.978307
0.983058 0.74562
0.670661 0.504729
0.857438 0.413001
The first digit is converted to a 0 for some reason and the negative ones become positive. Would anyone know why this is occurring?
int word;
is doing you no favours. First it's an integer so fin >> word only reads the integer portion of the inputs. 5.675207 is read as 5. the .675207 is left in the file stream for fin >> points[count]. Words isn't stored anywhere to the 5 is discarded but the .675207 lives on as 0.675207 in points[0].
Where the negative signs are going I didn't bother trying to figure out because
while (fin >> points[count])
{
++count;
}
fixes everything.
When you read in the numbers from the the file you are extracting them as "word" and then storing them as "points". "word" is an integer and "points" is a double, this will give you unexpected behavior. The compiler should give you warnings about this.
This program takes in an input, write it on a file character by character, count the amount of characters entered, then at the end copy it to an array of characters. The program works just fine until we get to the following snippet file.getline(arr, inputLength);. It changes the .txt file data and returns only the first character of the original input.
Any ideas?
#include <iostream>
#include <fstream>
using namespace std;
int getLine(char *& arr);
int main() {
char * arr = NULL;
cout << "Write something: ";
getLine(arr);
return 0;
}
int getLine(char *& arr) {
fstream file("temp.txt");
char input = '\0'; //initialize
int inputLength = 0; //initialize
if (file.is_open()) {
while (input != '\n') { //while the end of this line is not reached
input = cin.get(); //get each single character
file << input; //write it on a .txt file
inputLength++; //count the number of characters entered
}
arr = new char[inputLength]; //dynamically allocate memory for this array
file.getline(arr, inputLength); //HERE IS THE PROBLEM!!! ***
cout << "Count : " << inputLength << endl; //test counter
cout << "Array : " << arr << endl; //test line copy
file.close();
return 1;
}
return 0;
}
I see at least two problems with this code.
1) std::fstream constructor, by default, will open an existing file. It will not create a new one. If temp.txt does not exist, is_open() will fail. This code should pass the appropriate value for the second parameter to std::fstreams constructor that specifies that either a new file needs to be created, or the existing file is created.
Related to this: if the file already exists, running this code will not truncate it, so the contents of the file from this program's previous run will have obvious unexpected results.
2) The intent of this code appears to be to read back in the contents temp.txt that were previously written to it. To do that correctly, after writing and before reading it is necessary to seek back to the beginning of the file. This part appears to be missing.
There is no need in dynamic allocation because the std library functions get confused with mixed arguments such as cstring and pointer to cstring.I tested this code in Visual Studio 2015 compiler. It works good. Make sure to include all of the needed libraries:
#include <iostream>
#include <fstream>
#include<cstring>
#include<string>
using namespace std;
void getLine();
int main() {
cout << "Write something: ";
// no need to pass a pointer to a cstring
getLine();
system("pause");
return 0;
}
void getLine() {
char input[100]; // this is a cstring with
//a safe const number of elements
int inputLength; //to extract length of the actual input
//this function requires cstring as a first argument
// and constant length as a second
cin.get(input, 100, '\n'); //get each single character
//cast streamsize into int
inputLength = static_cast<int>(cin.gcount());
//testing input
cout << "Input: \n";
for (int i = 0; i < inputLength; i++)
{
cout << input[i];
}
cout << endl;
char arr[100];
strcpy_s(arr, input);
cout << "Count : " << inputLength << endl; //test counter
cout << "Array : " << endl; //test line copy
for (int i = 0; i < inputLength; i++)
{
cout << arr[i];
}
cout << endl;
// write cstring to a file
ofstream file;
file.open("temp.txt", ios::out);
if (file.is_open())
{
//write only what was entered in input
for (int i = 0; i < inputLength; i++)
file << arr[i];
file.close();
}
else cout << "Unable to open file";
}
I'm a student and I can't figure out how to complete this assignment. Basically were supposed to automatically compute a checksum on a datafile and store that checksum in an unsigned int array. The name of the file is supposed to be stored in another parallel array, and the contents of the file are to be read into a char array to compute the checksum.
This is what I have so far:
#include <iostream>
#include <string>
#include <iomanip>
#include <fstream>
#include <cstring>
using namespace std;
int main()
{
//declare variables
string filePath;
void savefile();
char choice;
int i,a, b, sum;
sum = 0;
a = 0;
b = 0;
ifstream inFile;
//arrays
const int SUM_ARR_SZ = 100;
string fileNames[SUM_ARR_SZ];
unsigned int checkSums[SUM_ARR_SZ];
do{
cout << "Please select: " << endl;
cout << " A) Compute checksum of specified file" << endl;
cout << " B) Verify integrity of specified file" << endl;
cout << " Q) Quit" << endl;
cin >> choice;
if (choice == 'a' || choice == 'A')
{
//open file in binary mode
cout << "Specify the file path: " << endl;
cin >> filePath;
inFile.open(filePath.c_str(), ios::binary);
//save file name
fileNames[a] = filePath;
a++;
//use seekg and tellg to determine file size
char Arr[100000];
inFile.seekg(0, ios_base::end);
int fileLen = inFile.tellg();
inFile.seekg(0, ios_base::beg);
inFile.read(Arr, fileLen);
inFile.close();
for (i = 0; i < 100000; i++)
{
sum += Arr[i];
}
//store the sum into checkSums array
checkSums[b] = sum;
b++;
cout <<" File checksum = "<< sum << endl;
}
if (choice == 'b' || choice == 'B')
{
cout << "Specify the file path: " << endl;
cin >> filePath;
if (strcmp(filePath.c_str(), fileNames[a].c_str())==0)
{
}
}
} while (choice != 'q' && choice != 'Q');
system("pause");
}
And an example of what our output is supposed to be(the 'a' is user input):
Please select:
A) Compute checksum of specified file
B) Verify integrity of specified file
Q) Quit
a
Specify the file path: c:\temp\tmp1
File checksum = 1530
Please select:
A) Compute checksum of specified file
B) Verify integrity of specified file
Q) Quit
Update: I've got the first part of the program sorted out now, the one which checks the sum. The problem I have now is getting the output correct for if you select B on the menu.
It's supposed to check both arrays and make sure the name is right and make sure that the checksums are the same, but I'm completely lost on how to put that into code.
The problem is the limit of your for loop. You have it reading 100000 times regardless of the length of the file. Changing 100000 to fileLen limits the read to each character read into Arr:
for (i = 0; i < fileLen; i++) {
sum += Arr[i];
}
output:
$ ./bin/cscpp
Please select:
A) Compute checksum of specified file
B) Verify integrity of specified file
Q) Quit
a
Specify the file path:
tmpkernel315.txt
File checksum = 46173
Change your code to read from file char by char.
File length is unknown.
Do this untill End Of File:
inFile.seekg(0, ios_base::end);
int fileLen = inFile.tellg();
inFile.seekg(0, ios_base::beg);
for(int i =0; i<fileLen; i++)
{
char Arr[1];
inFile.read(Arr, 1);
sum += Arr[0];
}
inFile.close();
//sum is your answer
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <fstream>
using namespace std;
void make_array(ifstream& num, int (&array)[50]);
int main()
{
ifstream file; // variable controlling the file
char filename[100]; /// to handle calling the file name;
int array[50];
cout << "Please enter the name of the file you wish to process:";
cin >> filename;
cout << "\n";
file.open(filename);
if (file.fail()) {
cout << "The file failed to open.\n";
exit(1);
} else {
cout << "File Opened Successfully.\n";
}
make_array(file, array);
file.close();
return (0);
}
void make_array(ifstream& num, int (&array)[50])
{
int i = 0; // counter variable
while (!num.eof() && i < 50) {
num >> array[i];
i = i + 1;
}
for (i; i >= 0; i--) {
cout << array[i] << "\n";
}
}
I am trying to read values from a file to an array using fstream. When I try to display the contents of the array, I get 2 really big negative numbers, and then the contents of the file.
Any ideas what I did wrong?
Your use of num.get(array[i]) doesn't match any of its signatures. See get method description. What you want is this:
array[i] = num.get();
As discussed in the comments, you try to read an integer which is encoded as text. For this, you need to use operator>> (which reads any type encoded as string) instead of get (which reads a single byte):
num >> array[i];