I'm trying to read some text out of a file called "file.dat". The problem is, that the string in the file does not include a zero at the end as for standard C. So I need something that adds the zero, so I can work with the string without getting random symbols after the string when I print it.
void cSpectrum::readSpectrum(const std::string &filename, double
tubeVoltage, double &minEnergy, std::string &spectrumName)
{
//Object with the name "inp" of the class ifstream
ifstream inp(filename, ios::binary);
//Checks if the file is open
if (!inp.is_open()) {
throw runtime_error("File not open!");
}
cout << "I opened the file!" << endl;
//Check the title of the file
string title;
char *buffer = new char[14];
inp.read(buffer, 14);
cout << buffer << endl;
}
At the moment I get the following output, I would like to get it without the ²²²²┘.
I opened the file!
x-ray spectrum²²²²┘
Simply allocate +1 more char for your array, but don't read into that char, just set it to 0:
char buffer[15];
inp.read(buffer, 14);
buffer[14] = '\0';
cout << buffer << endl;
Or, simply don't use a char[] at all, use std::string instead, see:
What is the best way to read an entire file into a std::string in C++?
I did it with the std::string now. If you want you can replace the 14 by an integer variable.
void cSpectrum::readSpectrum(const std::string & filename, double tubeVoltage, double
& minEnergy, std::string const & spectrumName){
ifstream inp(filename, ios::binary);
//Checks if the file is open
if (!inp.is_open()) {
throw runtime_error("ERROR: Could not open the file!");
}
//Reads the title
string title(14, '\0');
inp.read(&title[0], 14);
//If it is not the correct file throw an ERROR
if (title != spectrumName)
throw runtime_error("ERROR: Wrong file title");
readSpectrum(inp, tubeVoltage, minEnergy, spectrumName);
}
Related
E0304 no instance of overloaded function "std::basic_ifstream<_Elem, _Traits>::getline [with _Elem=char, _Traits=std::char_traits]" matches the argument list
Im using a struct for the Information:
struct customer {
int id;
char name;
char phone;
char address;
};
And im trying to write the Customers Information into a .txt file:
void customerData()
{
ifstream ifs;
ifs.open("Customer.txt");
int custNum = 0;
while (!ifs.eof())
{
ifs >> cust[custNum].id;
ifs.ignore();
ifs.getline(cust[custNum].name, 100, ';');
ifs.getline(cust[custNum].phone, 15, ';');
ifs.getline(cust[custNum].id, 15, ';');
ifs.getline(cust[custNum].address, 1500);
custNum++;
}
}
I cant figure out how to fix the above posted Error on the getline functions.
There are big mistakes in your code that guys pointed out.
You are not writing to the file, you are reading it.
You cannot store a full name in a single character.
Actually, if you want to store this data, you should use character array or std::string.
So your struct will be like this :
struct customer {
int ID;
char name[100];
char phone_number[15];
char address[1500];
/*
OR
int ID;
std::string name;
std::string phone_number;
std::string address;
in this case it's better to use std::string instead of using 1500 characters for address
*/
}
Also, getline is not for writing to the file (as you said you want to write in file) , it is used for reading from the file.
So your customerData function will look like this:
// saving in file
ofstream ofs(Customer.txt);
// check if file is created
if(ofs.is_open(){
ofs << name << '\n';
ofs << address << '\n';
ofs << phone_number << '\n';
ofs << id << '\n';
// This is a simple way to store data in a file.
// There are other ways to store data in a file..
// I used this because you can use getline to read them and get the data as lines.
}
I tried to take every character in a file and use with toupper() and tolower() functions. But I can't put the result instead of the character.
I used a vector to solve it.
Is there an easy way to solve this?
void UpperCase(){
fstream file;
char name[81] , ch;
vector<char> container;
cout << "Enter the file name : ";
cin >> name;
file.open(name,ios::in);
while(!file.eof() && !file.fail()){
file.get(ch);
container.push_back(toupper(ch));
}
file.close();
file.open(name,ios::out);
for(int i=0 ; i<container.size()-1 ; ++i){
file.put(container[i]);
}
file.close();
return;
}
Here is an efficient method:
char buffer[4096];
std::string name;
std::cout << "Enter filename: ";
std::cin >> name;
std::ifstream input(name.c_str(), ios::binary);
const std::string out_filename = name + ".upper_case";
std::ofstream output(out_filename.c_str(), ios::binary);
while (input.read(buffer, sizeof(buffer))
{
const unsigned int chars_read = input.gcount();
std::transform(&buffer[0], &buffer[chars_read],
&buffer[0], toupper);
output.write(buffer, chars_read);
}
The above code reads in a block of characters, then transforms them to uppercase, then writes the block to another file.
Writing to another file is a safe practice, and you don't need to read the entire file into memory.
You can change the size of the buffer to make the program more efficient. Recommend sizes are multiples of 512, since that is a standardized size for a hard drive sector.
Edit 1:
If you are allergic to std::transform, replace the call with a loop to convert the characters.
I tried making a program earlier that tells the user then number of char, words, and lines in a text file. I made functions to determine the numbers of each, yet I was passing them by value. This resulted in an error since after reading the number of char it would be at the end of the file and then output zero for the other two. Now I cant seem to rewrite my functions so that the file is open and closed each time its checked for char, words, and lines. Any one see where my errors are?? Thanks! (just copied and pasted one of my functions for now).
int num_of_lines(ifstream file)
{
string myfile;
myfile = argv[1];
ifstream l;
l.open(myfile);
int cnt3 = 0;
string str;
while(getline(file, str))cnt3++;
l.close();
return(cnt3);
}
int main(int argc, char **argv)
{
int num_of_char(ifstream file);
string file;
file = argv[1];
if(argc == 1)die("usage: mywc your_file");
ifstream ifs;
ifs.open(file);
if(ifs.is_open())
{
int a, b, c;
a = num_of_lines(ifs);
cout <<"Lines: " << a << endl;
}
else
{
cerr <<"Could not open: " << file << endl;
exit(1);
}
ifs.close();
return(0);
}
There is no way to "reopen" a file other than knowing the name and creating a new ifstream, but you can use the seekg member function to set your read position in the file, and setting it to 0 will have the next read operation start from the beginning of the file.
A stream is not possible to copy, so you can't pass it "by value", but must pass it by reference.
int num_of_lines(ifstream &file)
{
int count = 0;
string str;
while (getline(file, str)) {
count++;
}
file.seekg(0);
return count;
}
For the full problem, I agree with Mats Petersson, though. Counting both characters, lines and words in one pass will be much more efficient than reading through the file three times.
I am quite new to C++ and am trying to work out how to write a record in the format of this structure below to a text file:
struct user {
int id;
char username [20];
char password [20];
char name [20];
char email [30];
int telephone;
char address [70];
int level;
};
So far, I'm able to write to it fine but without an incremented id number as I don't know how to work out the number of records so the file looks something like this after I've written the data to the file.
1 Nick pass Nick email tele address 1
1 user pass name email tele address 1
1 test test test test test test 1
1 user pass Nick email tele addy 1
1 nbao pass Nick email tele 207 1
Using the following code:
ofstream outFile;
outFile.open("users.dat", ios::app);
// User input of data here
outFile << "\n" << 1 << " " << username << " " << password << " " << name << " "
<< email << " " << telephone << " " << address << " " << 1;
cout << "\nUser added successfully\n\n";
outFile.close();
So, how can I increment the value for each record on insertion and how then target a specific record in the file?
EDIT: I've got as far as being able to display each line:
if (inFile.is_open())
{
while(!inFile.eof())
{
cout<<endl;
getline(inFile,line);
cout<<line<<endl;
}
inFile.close();
}
What you have so far is not bad, except that it cannot handle cases where there is space in your strings (for example in address!)
What you are trying to do is write a very basic data base. You require three operations that need to be implemented separately (although intertwining them may give you better performance in certain cases, but I'm sure that's not your concern here).
Insert: You already have this implemented. Only thing you might want to change is the " " to "\n". This way, every field of the struct is in a new line and your problem with spaces are resolved. Later when reading, you need to read line by line
Search: To search, you need to open the file, read struct by struct (which itself consists of reading many lines corresponding to your struct fields) and identifying the entities of your interest. What to do with them is another issue, but simplest case would be to return the list of matching entities in an array (or vector).
Delete: This is similar to search, except you have to rewrite the file. What you do is basically, again read struct by struct, see which ones match your criteria of deletion. You ignore those that match, and write (like the insert part) the rest to another file. Afterwards, you can replace the original file with the new file.
Here is a pseudo-code:
Write-entity(user &u, ofstream &fout)
fout << u.id << endl
<< u.username << endl
<< u.password << endl
<< ...
Read-entity(user &u, ifstream &fin)
char ignore_new_line
fin >> u.id >> ignore_new_line
fin.getline(u.username, 20);
fin.getline(u.password, 20);
...
if end of file
return fail
Insert(user &u)
ofstream fout("db.dat");
Write-entity(u, fout);
fout.close();
Search(char *username) /* for example */
ifstream fin("db.dat");
user u;
vector<user> results;
while (Read-entity(u))
if (strcmp(username, u.username) == 0)
results.push_back(u);
fin.close();
return results;
Delete(int level) /* for example */
ifstream fin("db.dat");
ofstream fout("db_temp.dat");
user u;
while (Read-entity(u))
if (level != u.level)
Write-entity(u, fout);
fin.close();
fout.close();
copy "db_temp.dat" to "db.dat"
Side note: It's a good idea to place the \n after data has been written (so that your text file would end in a new line)
Using typical methods at least you will need to use fix size records if you want to have random access when reading the file so say you have 5 characters for name it will be stored as
bob\0\0
or whatever else you use to pad, this way you can index with record number * record size.
To increment the index you in the way you are doing you will need to the read the file to find the high existing index and increment it. Or you can load the file into memory and append the new record and write the file back
std::vector<user> users=read_dat("file.dat");
user user_=get_from_input();
users.push_back(user_);
then write the file back
std::ofstream file("file.dat");
for(size_t i=0; i!=users.size(); ++i) {
file << users.at(i);
//you will need to implement the stream extractor to do this easily
}
I suggest to wrap the file handler into a Class, and then overload the operator >> and << for your struct, with this was you will control the in and out.
For instance
struct User{
...
};
typedef std::vector<User> UserConT;
struct MyDataFile
{
ofstream outFile;
UserConT User_container;
MyDataFile(std::string const&); //
MyDataFile& operator<< (User const& user); // Implement and/or process the record before to write
MyDataFile& operator>> (UserConT & user); // Implement the extraction/parse and insert into container
MyDataFile& operator<< (UserConT const & user); //Implement extraction/parse and insert into ofstream
};
MyDataFile& MyDataFile::operator<< (User const& user)
{
static unsigned myIdRecord=User_container.size();
myIdRecord++;
outFile << user.id+myIdRecord << ....;
return *this;
}
int main()
{
MydataFile file("data.dat");
UserConT myUser;
User a;
//... you could manage a single record
a.name="pepe";
...
file<<a;
..//
}
A .Dat file is normally a simple text file itself that can be opened with notepad . So , you can simply read the Last Line of the file , read it , extract the first character , convert it into integer . THen increment the value and be done .
Some sample code here :
#include <iostream.h>
#include <fstream.h>
using namespace std;
int main(int argc, char *argv[])
{
ifstream in("test.txt");
if(!in) {
cout << "Cannot open input file.\n";
return 1;
}
char str[255];
while(in) {
in.getline(str, 255); // delim defaults to '\n'
//if(in) cout << str << endl;
}
// Now str contains the last line ,
if ((str[0] >=48) || ( str[0] <=57))
{
int i = atoi(str[0]);
i++;
}
//i contains the latest value , do your operation now
in.close();
return 0;
}
Assuming your file format doesn't not need to be human readable.
You can write the struct out to file such as.
outFile.open("users.dat", ios::app | ios::binary);
user someValue = {};
outFile.write( (char*)&someValue, sizeof(user) );
int nIndex = 0;
user fetchValue = {};
ifstream inputFile.open("user.data", ios::binary);
inputFile.seekg (0, ios::end);
int itemCount = inputFile.tellg() / sizeof(user);
inputFile.seekg (0, ios::beg);
if( nIndex > -1 && nIndex < itemCount){
inputFile.seekg ( sizeof(user) * nIndex , ios::beg);
inputFile.read( (char*)&fetchValue, sizeof(user) );
}
The code that writes to the file is a member function of the user struct?
Otherwise I see no connection with between the output and the struct.
Possible things to do:
write the id member instead of 1
use a counter for id and increment it at each write
don't write the id and when reading use the line number as id
If I include the if test in my code the error message is returned and I'm not sure why.
and when it's not used, my program get's stuck in a loop where it never reaches the end of the file. I don't understand what's going wrong.
int countlines()
{
fstream myfile;
myfile.open("questions.txt", ios::in);
string contents;
int linenumber = 0;
//if (myfile.is_open())
// {
while (!myfile.eof())
{
getline( myfile, contents );
if (contents != "")
{
linenumber++;
}
}
cout << "there are " << linenumber << " lines.\n";
//}else {cout<<"Unable to get file.\n";}
myfile.close();
return(linenumber);
}
What's going on is that your file is not being opened. That's why is_open fails.
Then, when you comment out the check, you're breaking your loop because you're iterating incorrectly (see my comment) and not detecting stream failures (.eof() will never be true on that stream).
Make sure that the file is in the right place, and that it is accessible.
The correct idiom for reading a file line-by-line in C++ is using a loop like this:
for (std::string line; std::getline(file,line);)
{
// process line.
}
Inserting this in your example (+fixing indentation and variable names) gives something like this:
int countlines(const std::string& path)
{
// Open the file.
std::ifstream file(path.c_str());
if (!file.is_open()) {
return -1; // or better, throw exception.
}
// Count the lines.
int count = 0;
for (std::string line; std::getline(file,line);)
{
if (!line.empty()) {
++count;
}
}
return count;
}
Note that if you don't intend to process the line contents, you can actually skip processing them using std::streambuf_iterator, which can make your code look like:
int countlines(const std::string& path)
{
// Open the file.
std::ifstream file(path.c_str());
if (!file.is_open()) {
return -1; // or better, throw exception.
}
// Refer to the beginning and end of the file with
// iterators that process the file character by character.
std::istreambuf_iterator<char> current(file);
const std::istreambuf_iterator<char> end;
// Count the number of newline characters.
return std::count(current, end, '\n');
}
The second version will completely bypass copying the file contents and avoid allocating large chunks of memory for long lines.
When using std::istream and std::ostream (whose std::fstream implements), the recommended usage is to directly use the stream in a bool context instead of calling eof() function because it only return true when you managed to read until the last byte of the file. If there was any error before that, the function will still return true.
So, you should have written your code as:
int countlines() {
ifstream myfile;
int linenumber = 0;
string linecontent;
myfile.open("question.txt", ios::in);
while (getline(myfile, linecontent)) {
if (!linecontent.empty()) {
++linenumber;
}
}
return linenumber;
}
Try the following code. It will also (hopefully) give you an idea why the file open is failing...
int countlines()
{
ifstream myfile;
myfile.open("questions.txt");
string contents;
int linenumber = 0;
if (myfile.is_open())
{
while (getline(myfile, contents))
{
if (contents != "")
linenumber++;
}
cout << "there are " << linenumber << " lines." << endl;
myfile.close();
}
else
cout << "Unable to get file (reason: " << strerror(errno) << ")." << endl;
return linenumber;
}