When I run the following program and paste 50000 symbols to the command line, the program gets 4096 symbols only. Could you please suggest me what to do in order to get the full list of symbols?
#include <iostream>
#include <string>
using namespace std;
int main()
{
char temp[50001];
while (cin.getline(temp, 50001, '\n'))
{
string s(temp);
cout << s.size() << endl;
}
return 0;
}
P.S.
When I read the symbols from file using fstream, it's OK
I'm taking a leap jump here but since many powershell terminals have 4096 truncation limits (take a look at the Out-File documentation), this is likely a Windows command line limitation rather than a getline limitation.
The same problem has been encountered previously by others: https://github.com/Discordia/large-std-input/blob/master/LargeStdInput/Main.cpp
I don't understand why you are reading into a character array, then transferring it into a string.
In any case, your issue may be with repeated allocations.
Reading into std::string directly
Two simple lines:
std::string s;
getline(cin, s, '\n');
Reading into an array first
Yes, there is a simpler method:
#define BUFFER_SIZE 8196 // Very important, named constant
char temp[BUFFER_SIZE];
cin.getline(temp, BUFFER_SIZE, '\n');
// Get the number of characters actually read
unsigned int chars_read = cin.gcount();
std::string s(temp, chars_read); // Here's how to transfer the characters.
Using a debugger, you need to view the value in chars_read to verify that the quantity of characters read is valid.
Binary reading
Some platforms provide translations between the data read and your program. For example, Windows uses Ctrl-Z as an EOF character; Linux uses Ctrl-D.
The input data may use UTF encoding and contain values outside the range of ASCII printable set.
So, the preferred method is to read from a stream opened in binary mode. Unfortunately, cin cannot be opened easily in binary mode.
See Open cin in binary
The preferred method, if possible, is to put the text into a file and read from the file.
Related
I wanted to use fstream to read a txt file.
I am using inFile >> characterToConvert, but the problem is that this omits any spaces and newline.
I am writing an encryption program so I need to include the spaces and newlines.
What would be the proper way to go about accomplishing this?
Probably the best way is to read the entire file's contents into a string, which can be done very easily using ifstream's rdbuf() method:
std::ifstream in("myfile");
std::stringstream buffer;
buffer << in.rdbuf();
std::string contents(buffer.str());
You can then use regular string manipulation now that you've got everything from the file.
While Tomek was asking about reading a text file, the same approach will work for reading binary data, though the std::ios::binary flag needs to be provided when creating the input file stream.
For encryption, you're better off opening your file in binary mode. Use something like this to put the bytes of a file into a vector:
std::ifstream ifs("foobar.txt", std::ios::binary);
ifs.seekg(0, std::ios::end);
std::ifstream::pos_type filesize = ifs.tellg();
ifs.seekg(0, std::ios::beg);
std::vector<char> bytes(filesize);
ifs.read(&bytes[0], filesize);
Edit: fixed a subtle bug as per the comments.
I haven't tested this, but I believe you need to clear the "skip whitespace" flag:
inFile.unsetf(ios_base::skipws);
I use the following reference for C++ streams:
IOstream Library
std::ifstream ifs( "filename.txt" );
std::string str( ( std::istreambuf_iterator<char>( ifs ) ),
std::istreambuf_iterator<char>()
);
The following c++ code will read an entire file...
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main ()
{
string line;
ifstream myfile ("foo.txt");
if (myfile.is_open()){
while (!myfile.eof()){
getline (myfile,line);
cout << line << endl;
}
myfile.close();
}
return 0;
}
post your code and I can give you more specific help to your problem...
A lot of the benefit of the istream layer is providing basic formatting and parsing for simple types ro and from a stream. For the purposes that you describe, none of this is really important and you are just interested in the file as a stream of bytes.
For these purpose you may be better of just using the basic_streambuf interface provided by a filebuf. The 'skip whitespace' behaviour is part of the istream interface functionality that you just don't need.
filebuf underlies an ifstream, but it is perfectly valid to use it directly.
std::filebuf myfile;
myfile.open( "myfile.dat", std::ios_base::in | std::ios_base::binary );
// gets next char, then moves 'get' pointer to next char in the file
int ch = myfile.sbumpc();
// get (up to) the next n chars from the stream
std::streamsize getcount = myfile.sgetn( char_array, n );
Also have a look at the functions snextc (moves the 'get' pointer forward and then returns the current char), sgetc (gets the current char but doesn't move the 'get' pointer) and sungetc (backs up the 'get' pointer by one position if possible).
When you don't need any of the insertion and extraction operators provided by an istream class and just need a basic byte interface, often the streambuf interface (filebuf, stringbuf) is more appropriate than an istream interface (ifstream, istringstream).
You can call int fstream::get(), which will read a single character from the stream. You can also use istream& fstream::read(char*, streamsize), which does the same operation as get(), just over multiple characters. The given links include examples of using each method.
I also recommend reading and writing in binary mode. This allows ASCII control characters to be properly read from and written to files. Otherwise, an encrypt/decrypt operation pair might result in non-identical files. To do this, you open the filestream with the ios::binary flag. With a binary file, you want to use the read() method.
Another better way is to use istreambuf_iterator, and the sample code is as below:
ifstream inputFile("test.data");
string fileData(istreambuf_iterator<char>(inputFile), istreambuf_iterator<char>());
For encryption, you should probably use read(). Encryption algorithms usually deal with fixed-size blocks. Oh, and to open in binary mode (no translation frmo \n\r to \n), pass ios_base::binary as the second parameter to constructor or open() call.
Simple
#include <fstream>
#include <iomanip>
ifstream ifs ("file");
ifs >> noskipws
that's all.
ifstream ifile(path);
std::string contents((std::istreambuf_iterator<char>(ifile)), std::istreambuf_iterator<char>());
ifile.close();
I also find that the get() method of ifstream object can also read all the characters of the file, which do not require unset std::ios_base::skipws. Quote from C++ Primer:
Several of the unformatted operations deal with a stream one byte at a time. These operations, which are described in Table 17.19, read rather ignore whitespaces.
These operations are list as below:
is.get(), os.put(), is.putback(), is.unget() and is.peek().
Below is a minimum working code
#include <iostream>
#include <fstream>
#include <string>
int main(){
std::ifstream in_file("input.txt");
char s;
if (in_file.is_open()){
int count = 0;
while (in_file.get(s)){
std::cout << count << ": "<< (int)s <<'\n';
count++;
}
}
else{
std::cout << "Unable to open input.txt.\n";
}
in_file.close();
return 0;
}
The content of the input file (cat input.txt) is
ab cd
ef gh
The output of the program is:
0: 97
1: 98
2: 32
3: 99
4: 100
5: 10
6: 101
7: 102
8: 32
9: 103
10: 104
11: 32
12: 10
10 and 32 are decimal representation of newline and space character. Obviously, all characters have been read.
As Charles Bailey correctly pointed out, you don't need fstream's services just to read bytes. So forget this iostream silliness, use fopen/fread and be done with it. C stdio is part of C++, you know ;)
I need to make a program in C++ that must read and write text files line by line with an specific format, but the problem is that in my PC I work in Windows, and in College they have Linux and I am having problems because of line endings are different in these OS.
I am new to C++ and don't know could I make my program able read the files no matter if they were written in Linux or Windows. Can anybody give me some hints? thanks!
The input is like this:
James White 34 45.5 10 black
Miguel Chavez 29 48.7 9 red
David McGuire 31 45.8 10 blue
Each line being a record of a struct of 6 variables.
Using the std::getline overload without the last (i.e. delimiter) parameter should take care of the end-of-line conversions automatically:
std::ifstream in("TheFile.txt");
std::string line;
while (std::getline(in, line)) {
// Do something with 'line'.
}
Here's a simple way to strip string of an extra "\r":
std::ifstream in("TheFile.txt");
std::string line;
std::getline(input, line));
if (line[line.size() - 1] == '\r')
line.resize(line.size() - 1);
If you can already read the files, just check for all of the newline characters like "\n" and "\r". I'm pretty sure that linux uses "\r\n" as the newline character.
You can read this page: http://en.wikipedia.org/wiki/Newline
and here is a list of all the ascii codes including the newline characters:
http://www.asciitable.com/
Edit: Linux uses "\n", Windows uses "\r\n", Mac uses "\r". Thanks to Seth Carnegie
Since the result will be CR LF, I would add something like the following to consume the extras if they exist. So once your have read you record call this before trying to read the next.
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
If you know the number of values you are going to read for each record you could simply use the ">>" method. For example:
fstream f("input.txt" std::ios::in);
string tempStr;
double tempVal;
for (number of records) {
// read the first name
f >> tempStr;
// read the last name
f >> tempStr;
// read the number
f >> tempVal;
// and so on.
}
Shouldn't that suffice ?
Hi I will give you the answer in stages. Please go trough in order to understand the code.
Stage 1: Design our program:
Our program based on the requirements should...:
...include a definition of a data type that would hold the data. i.e. our
structure of 6 variables.
...provide user interaction i.e. the user should be able to
provide the program, the file name and its location.
...be able to
open the chosen file.
...be able to read the file data and
write/save them into our structure.
...be able to close the file
after the data is read.
...be able to print out of the saved data.
Usually you should split your code into functions representing the above.
Stage 2: Create an array of the chosen structure to hold the data
...
#define MAX 10
...
strPersonData sTextData[MAX];
...
Stage 3: Enable user to give in both the file location and its name:
.......
string sFileName;
cout << "Enter a file name: ";
getline(cin,sFileName);
ifstream inFile(sFileName.c_str(),ios::in);
.....
->Note 1 for stage 3. The accepted format provided then by the user should be:
c:\\SomeFolder\\someTextFile.txt
We use two \ backslashes instead of one \, because we wish it to be treated as literal backslash.
->Note 2 for stage 3. We use ifstream i.e. input file stream because we want to read data from file. This
is expecting the file name as c-type string instead of a c++ string. For this reason we use:
..sFileName.c_str()..
Stage 4: Read all data of the chosen file:
...
while (!inFile.eof()) { //we loop while there is still data in the file to read
...
}
...
So finally the code is as follows:
#include <iostream>
#include <fstream>
#include <cstring>
#define MAX 10
using namespace std;
int main()
{
string sFileName;
struct strPersonData {
char c1stName[25];
char c2ndName[30];
int iAge;
double dSomeData1; //i had no idea what the next 2 numbers represent in your code :D
int iSomeDate2;
char cColor[20]; //i dont remember the lenghts of the different colors.. :D
};
strPersonData sTextData[MAX];
cout << "Enter a file name: ";
getline(cin,sFileName);
ifstream inFile(sFileName.c_str(),ios::in);
int i=0;
while (!inFile.eof()) { //loop while there is still data in the file
inFile >>sTextData[i].c1stName>>sTextData[i].c2ndName>>sTextData[i].iAge
>>sTextData[i].dSomeData1>>sTextData[i].iSomeDate2>>sTextData[i].cColor;
++i;
}
inFile.close();
cout << "Reading the file finished. See it yourself: \n"<< endl;
for (int j=0;j<i;j++) {
cout<<sTextData[j].c1stName<<"\t"<<sTextData[j].c2ndName
<<"\t"<<sTextData[j].iAge<<"\t"<<sTextData[j].dSomeData1
<<"\t"<<sTextData[j].iSomeDate2<<"\t"<<sTextData[j].cColor<<endl;
}
return 0;
}
I am going to give you some exercises now :D :D
1) In the last loop:
for (int j=0;j<i;j++) {
cout<<sTextData[j].c1stName<<"\t"<<sTextData[j].c2ndName
<<"\t"<<sTextData[j].iAge<<"\t"<<sTextData[j].dSomeData1
<<"\t"<<sTextData[j].iSomeDate2<<"\t"<<sTextData[j].cColor<<endl;}
Why do I use variable i instead of lets say MAX???
2) Could u change the program based on stage 1 on sth like:
int main(){
function1()
function2()
...
functionX()
...return 0;
}
I hope i helped...
I was attempting to read a binary file byte by byte using an ifstream. I've used istream methods like get() before to read entire chunks of a binary file at once without a problem. But my current task lends itself to going byte by byte and relying on the buffering in the io-system to make it efficient. The problem is that I seemed to reach the end of the file several bytes sooner than I should. So I wrote the following test program:
#include <iostream>
#include <fstream>
int main() {
typedef unsigned char uint8;
std::ifstream source("test.dat", std::ios_base::binary);
while (source) {
std::ios::pos_type before = source.tellg();
uint8 x;
source >> x;
std::ios::pos_type after = source.tellg();
std::cout << before << ' ' << static_cast<int>(x) << ' '
<< after << std::endl;
}
return 0;
}
This dumps the contents of test.dat, one byte per line, showing the file position before and after.
Sure enough, if my file happens to have the two-byte sequence 0x0D-0x0A (which corresponds to carriage return and line feed), those bytes are skipped.
I've opened the stream in binary mode. Shouldn't that prevent it from interpreting line separators?
Do extraction operators always use text mode?
What's the right way to read byte by byte from a binary istream?
MSVC++ 2008 on Windows.
The >> extractors are for formatted input; they skip white space (by
default). For single character unformatted input, you can use
istream::get() (returns an int, either EOF if the read fails, or
a value in the range [0,UCHAR_MAX]) or istream::get(char&) (puts the
character read in the argument, returns something which converts to
bool, true if the read succeeds, and false if it fails.
there is a read() member function in which you can specify the number of bytes.
Why are you using formatted extraction, rather than .read()?
source.get()
will give you a single byte. It is unformatted input function.
operator>> is formatted input function that may imply skipping whitespace characters.
As others mentioned, you should use istream::read(). But, if you must use formatted extraction, consider std::noskipws.
Edit: I'm trying to convert a text file into bytes. I'm not sure if the code is turning it into bytes or not. Here is the link to the header so you can see the as_bytes function.
link
#include "std_lib_facilities.h"
int main()
{
cout << "Enter input file name.\n";
string file;
cin >> file;
ifstream in(file.c_str(), ios::binary);
int i;
vector<int> bin;
while(in.read(as_bytes(i), sizeof(int)))
bin.push_back(i);
ofstream out(file.c_str(), ios::out);
for(int i = 0; i < bin.size(); ++i)
out << bin[i];
keep_window_open();
}
Note that now the out stream just outputs the contents of the vector. It doesn't use the write function or the binary mode. This converts the file to a large line of numbers - is this what I'm looking for?
Here is an example of the second code's file conversion:
that guy likes to eat lots of pie (not sure if this was exact text)
turns to
543518319544825700191924850016351970295432362115448292821701667182186922608417526375411952522351186935715718643976841768956006
The reason your first method didn't change the file is because all files are stored in the same way. The only "difference" between text files and binary files is that text files contain only bytes that can be shown as ASCII characters, while binary files* have a much more random variety and order of bytes. So you are reading bytes in as bytes and then outputting them as bytes again!
*I'm including Unicode text files as binary, since they can have multiple bytes to denote one character point, depending on the character point and the encoding used.
The second method is also fairly simple. You are reading in the bytes, as before, and storing them in integers (which are probably 4 bytes long). Then you are just printing out the integers as if they are integers, so you are seeing a string of numbers.
As for why your first method cut off some of the bytes, you're right in that it's probably some bug in your code. I thought it was more important to explain what the ideas are in this case, rather than debug some test code.
I wanted to use fstream to read a txt file.
I am using inFile >> characterToConvert, but the problem is that this omits any spaces and newline.
I am writing an encryption program so I need to include the spaces and newlines.
What would be the proper way to go about accomplishing this?
Probably the best way is to read the entire file's contents into a string, which can be done very easily using ifstream's rdbuf() method:
std::ifstream in("myfile");
std::stringstream buffer;
buffer << in.rdbuf();
std::string contents(buffer.str());
You can then use regular string manipulation now that you've got everything from the file.
While Tomek was asking about reading a text file, the same approach will work for reading binary data, though the std::ios::binary flag needs to be provided when creating the input file stream.
For encryption, you're better off opening your file in binary mode. Use something like this to put the bytes of a file into a vector:
std::ifstream ifs("foobar.txt", std::ios::binary);
ifs.seekg(0, std::ios::end);
std::ifstream::pos_type filesize = ifs.tellg();
ifs.seekg(0, std::ios::beg);
std::vector<char> bytes(filesize);
ifs.read(&bytes[0], filesize);
Edit: fixed a subtle bug as per the comments.
I haven't tested this, but I believe you need to clear the "skip whitespace" flag:
inFile.unsetf(ios_base::skipws);
I use the following reference for C++ streams:
IOstream Library
std::ifstream ifs( "filename.txt" );
std::string str( ( std::istreambuf_iterator<char>( ifs ) ),
std::istreambuf_iterator<char>()
);
The following c++ code will read an entire file...
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main ()
{
string line;
ifstream myfile ("foo.txt");
if (myfile.is_open()){
while (!myfile.eof()){
getline (myfile,line);
cout << line << endl;
}
myfile.close();
}
return 0;
}
post your code and I can give you more specific help to your problem...
A lot of the benefit of the istream layer is providing basic formatting and parsing for simple types ro and from a stream. For the purposes that you describe, none of this is really important and you are just interested in the file as a stream of bytes.
For these purpose you may be better of just using the basic_streambuf interface provided by a filebuf. The 'skip whitespace' behaviour is part of the istream interface functionality that you just don't need.
filebuf underlies an ifstream, but it is perfectly valid to use it directly.
std::filebuf myfile;
myfile.open( "myfile.dat", std::ios_base::in | std::ios_base::binary );
// gets next char, then moves 'get' pointer to next char in the file
int ch = myfile.sbumpc();
// get (up to) the next n chars from the stream
std::streamsize getcount = myfile.sgetn( char_array, n );
Also have a look at the functions snextc (moves the 'get' pointer forward and then returns the current char), sgetc (gets the current char but doesn't move the 'get' pointer) and sungetc (backs up the 'get' pointer by one position if possible).
When you don't need any of the insertion and extraction operators provided by an istream class and just need a basic byte interface, often the streambuf interface (filebuf, stringbuf) is more appropriate than an istream interface (ifstream, istringstream).
You can call int fstream::get(), which will read a single character from the stream. You can also use istream& fstream::read(char*, streamsize), which does the same operation as get(), just over multiple characters. The given links include examples of using each method.
I also recommend reading and writing in binary mode. This allows ASCII control characters to be properly read from and written to files. Otherwise, an encrypt/decrypt operation pair might result in non-identical files. To do this, you open the filestream with the ios::binary flag. With a binary file, you want to use the read() method.
Another better way is to use istreambuf_iterator, and the sample code is as below:
ifstream inputFile("test.data");
string fileData(istreambuf_iterator<char>(inputFile), istreambuf_iterator<char>());
For encryption, you should probably use read(). Encryption algorithms usually deal with fixed-size blocks. Oh, and to open in binary mode (no translation frmo \n\r to \n), pass ios_base::binary as the second parameter to constructor or open() call.
Simple
#include <fstream>
#include <iomanip>
ifstream ifs ("file");
ifs >> noskipws
that's all.
ifstream ifile(path);
std::string contents((std::istreambuf_iterator<char>(ifile)), std::istreambuf_iterator<char>());
ifile.close();
I also find that the get() method of ifstream object can also read all the characters of the file, which do not require unset std::ios_base::skipws. Quote from C++ Primer:
Several of the unformatted operations deal with a stream one byte at a time. These operations, which are described in Table 17.19, read rather ignore whitespaces.
These operations are list as below:
is.get(), os.put(), is.putback(), is.unget() and is.peek().
Below is a minimum working code
#include <iostream>
#include <fstream>
#include <string>
int main(){
std::ifstream in_file("input.txt");
char s;
if (in_file.is_open()){
int count = 0;
while (in_file.get(s)){
std::cout << count << ": "<< (int)s <<'\n';
count++;
}
}
else{
std::cout << "Unable to open input.txt.\n";
}
in_file.close();
return 0;
}
The content of the input file (cat input.txt) is
ab cd
ef gh
The output of the program is:
0: 97
1: 98
2: 32
3: 99
4: 100
5: 10
6: 101
7: 102
8: 32
9: 103
10: 104
11: 32
12: 10
10 and 32 are decimal representation of newline and space character. Obviously, all characters have been read.
As Charles Bailey correctly pointed out, you don't need fstream's services just to read bytes. So forget this iostream silliness, use fopen/fread and be done with it. C stdio is part of C++, you know ;)