I have an assignment that wants plain text data to be read in from a file, and then outputted to a separate binary file. With that being said, I expect to see that the contents of the binary file not to be intelligible for human reading. However, when I open the binary file the contents are still appearing as plain text. I am setting the mode like this _file.open(OUTFILE, std::ios::binary). I can't seem to figure out what I'm missing. I've followed other examples with different methods of implementation, but there's obviously something I'm missing.
For the purpose of posting, I created a slimmed down test case to demonstrate what I'm attempting.
Thanks in advance, help is greatly appreciated!
Input File: test.txt
Hello World
main.cpp
#include <iostream>
#include <fstream>
using namespace std;
#define INFILE "test.txt"
#define OUTFILE "binary-output.dat"
int main(int argc, char* argv[]) {
char* text = nullptr;
int nbytes = 0;
// open text file
fstream input(INFILE, std::ios::in);
if (!input) {
throw "\n***Failed to open file " + string(INFILE) + " ***\n";
}
// copy from file into memory
input.seekg(0, std::ios::end);
nbytes = (int)input.tellg() + 1;
text = new char[nbytes];
input.seekg(ios::beg);
int i = 0;
input >> noskipws;
while (input.good()) {
input >> text[i++];
}
text[nbytes - 1] = '\0';
cout << "\n" << nbytes - 1 << " bytes copied from file " << INFILE << " into memory (null byte added)\n";
if (!text) {
throw "\n***No data stored***\n";
} else {
// open binary file for writing
ofstream _file;
_file.open(OUTFILE, std::ios::binary);
if (!_file.is_open()) {
throw "\n***Failed to open file***\n";
} else {
// write data into the binary file and close the file
for (size_t i = 0U; i <= strlen(text); ++i) {
_file << text[i];
}
_file.close();
}
}
}
As stated here, std::ios::binary isn't actually going to write binary for you. Basically, it's the same as std::ios::out except things like \n aren't converted to line breaks.
You can convert text to binary by using <bitset>, like this:
#include <iostream>
#include <vector>
#include <bitset>
int main() {
std::string str = "String in plain text";
std::vector<std::bitset<8>> binary; // A vector of binaries
for (unsigned long i = 0; i < str.length(); ++i) {
std::bitset<8> bs4(str[i]);
binary.push_back(bs4);
}
return 0;
}
And then write to your file.
In simplest terms, the flag std::ios::binary means:
Do not make any adjustments to my output to aid in readability or conformance to operating system standards. Write exactly what I send.
In your case, you are writing readable text and the file contains exactly what you sent.
You could also write bytes that are unintelligible when viewed as text. In that case, your file would be unintelligible when viewed as text.
Related
I would like to access a file through fstream with the following requirements:
If the files does not exists, it create it
The file can be read (from pos 0)
The file can be (over)written (from pos 0)
Without closing and re-opening the file
ios_base::in seems to disable file creation
ios_base::out seems to disable file reading
Is this possible? How?
#include <iostream>
#include <sstream>
#include <fstream>
#include <cassert>
using namespace std;
int main()
{
auto mode = ios_base::in|ios_base::out;
std::string filePath = "./test.txt";
std::string content1 = "Any content 1";
std::string content2 = "Any content 2";
{
std::remove(filePath.c_str());
}
{// Test creation
// make sure test.txt is missing / does not exists
fstream file(filePath, mode);
assert(file.is_open() && file.good());
file << content1;
}
{ // Test reading & writing
fstream file(filePath, mode);
// read
file.seekg(0);
std::stringstream buffer1;
buffer1 << file.rdbuf();
cout << buffer1.str() << endl;
assert(buffer1.str()==content1);
// write
file.seekp(0);
file << content2;
assert(file.is_open() && file.good());
// read
file.seekg(0);
std::stringstream buffer2;
buffer2 << file.rdbuf();
cout << buffer2.str() << endl;
assert(buffer2.str()==content2);
}
return 0;
}
Run it
Only with fstream I'd say no.
You might want to have something similar with the trunc mode but you'll lose everything if the file exists (which might be a problem, if not go for trunc + out)
The other way is to check if the file exists, if not you create it (whichever way). Then you open with In and Out and do your stuff.
It kind of doesn't make sense to be able to read inside an empty file you just created from the cpp point of view
I am trying to count the characters in my program. Initially my variable "words" was a char and the file read just fine. When trying to determine the length of the variable, it wouldn't work with .length(). Can you explain how I can make my "words" variable as a string so that the words.length() executes correctly?
error on line words = readFile.get(); is:
no match for ‘operator!=’ in ‘words != -0x00000000000000001’
#include <iostream>
#include <cmath>
#include <fstream>
#include <cstdlib>
#include <string>
#include <stdio.h>
#include <math.h>
using namespace std;
int main() {
//buff array to hold char words in the input text file
string words;
//char words;
//read file
ifstream readFile("TextFile1.txt");
//notify user if the file didn't transfer into the system
if (!readFile)
cout <<"I am sorry but we could not process your file."<<endl;
//read and output the file
while (readFile)
{
words = readFile.get();
if(words!= EOF)
cout <<words;
}
cout << "The size of the file is: " << words.length() << " bytes. \n";
return 0;
}
char c;
while (readFile.get(c))
{
words.insert(c);
}
Of course, if you were solely doing this to count the number of characters (and were intent on using std::istream::get) you'd probably be better off just doing this:
int NumChars = 0;
while (readFile.get())
{
NumChars++;
}
Oh, and by the way, you might want to close the file after you're done with it.
You should read some reference.. try cppreference.com and look for std::instream::get
I'm not sure what do you want, but if you wanna just count words, you can do something like this:
std::ifstream InFile(/*filename*/);
if(!InFile)
// file not found
std::string s;
int numWords = 0;
while(InFile >> s)
numWords++;
std::cout << numWords;
Or if you want to get to know how many characters are in file, change std::string s to char s and use std::ifstream::get instead:
std::ifstream InFile(/*filename*/);
if(!InFile)
// file not found
char s;
int numCharacters = 0;
while(InFile.get(s)) //this will read one character after another until EOF
numCharacters++;
std::cout << numCharacters;
The second approach is easier:
If file uses ASCII, numCharacters == fileSize;
Otherwise if it uses UNICODE, numCharacters == fileSize / 2;
get() returns an int, to do what you're doing, you must check that int before appending to "words" instead of checking words against EOF, e.g.:
...
//read and output the file
while (readFile)
{
const int w = readFile.get();
if (w!= EOF) {
words += w;
cout <<words;
}
}
...
I am under the impression fstream objects in c++ can be used to both read and write, using the same stream.
I have successfully been able to first write to a stream and then read from it. If I however try to write to it again the file is not affected.
Here is a code example that successfully compiles on windows using MinGw:
int main()
{
std::string path="file.txt";
std::fstream fs(path.c_str());
int buffSize=100;
int bytesRead=0;
char* buffer=new char[buffSize];
fs.write("hello", 5);
fs.seekp(0, std::ios::beg);
fs.read(buffer, buffSize);
bytesRead=fs.gcount();
for(int i=0;i<bytesRead;i++) {std::cout << buffer[i];}
std::cout << "\n";
fs.clear();
fs.seekp(1, std::ios::beg);
fs.write("E", 1);
std::cout << "fail: " << fs.fail() << "\n";
delete[] buffer;
}
The initial content of "file.txt" was only:
AAAAAAA
And the program outputs:
helloAA
fail: 0
Looking at the file in a text editor after running the program shows that the final content is:
helloAA
The final writing of the "E" has not taken effect, why is this and how do I fix it?
EDIT:
I tried using fs.clear() before writing again as user 0x499602D2 suggested. Also added a line printing out whether the failbit or badbit has been set or not and updated the program output. The final file content stays the same however, the problem remains.
(more verbose answer from what I posted in comments on the question)
You need to call flush() on output stream objects (derived from ostream) in order for the data to actually be written on the output stream. More information on flush() is available on this c++ reference page.
This work in GCC 4.9.0 and VS2013.
Notes:
seekg is for move the read pointer
seekp is for move the write pointer
In the sample code in line fs.seekp(0, std::ios::beg); need to be seekg. There is no problem because the read pointer has not been move (there is no read until there).
Code:
#include <algorithm>
#include <iostream>
#include <fstream>
using namespace std;
int main(int argc, char* argv[]) {
std::string path = "H:\\save.txt";
int buffSize = 100;
int bytesRead = 0;
char* buffer = new char[buffSize];
std::fstream fs(path.c_str());
fs.write("hello", 5);
fs.flush(); // flushing to disk file
fs.seekg(0, std::ios_base::beg); // moving the read pointer
fs.read(buffer, buffSize);
bytesRead = fs.gcount();
for (int i = 0; i < bytesRead; i++) {
std::cout << buffer[i];
}
std::cout << "\n";
fs.clear();
fs.seekp(1, std::ios::beg);
fs.write("E", 1);
fs.flush(); // flushing to disk file
std::cout << "fail: " << fs.fail() << "\n";
delete[] buffer;
return 0;
}
string data="";
string Newdata="New Data";
std::fstream output_file(fileName, ios::in| ios::out);
output_file >> data; //read Data
output_file.seekg( 0, ios::beg );//set point to zero
output_file<<Newdata<<"\n"; //write new Data
output_file.close();
once you read a file using fstream, tellg < read pointer > and tellp < write pointer > points to -1.
to be able to write again using fstream, just call fstream.clear() and it will reset read and write pointer to where it was before reading.
none of the solution posted above work but fstream.clear() works.
I need to read a jpg file to a string. I want to upload this file to our server, I just find out that the API requires a string as the data of this pic. I followed the suggestions in a former question I've asked Upload pics to a server using c++ .
int main() {
ifstream fin("cloud.jpg");
ofstream fout("test.jpg");//for testing purpose, to see if the string is a right copy
ostringstream ostrm;
unsigned char tmp;
int count = 0;
while ( fin >> tmp ) {
++count;//for testing purpose
ostrm << tmp;
}
string data( ostrm.str() );
cout << count << endl;//ouput 60! Definitely not the right size
fout << string;//only 60 bytes
return 0;
}
Why it stops at 60? It's a strange character at 60, and what should I do to read the jpg to a string?
UPDATE
Almost there, but after using the suggested method, when I rewrite the string to the output file, it distorted. Find out that I should also specify that the ofstream is in binary mode by ofstream::binary. Done!
By the way what's the difference between ifstream::binary & ios::binary, is there any abbreviation for ofstream::binary?
Open the file in binary mode, otherwise it will have funny behavior, and it will handle certain non-text characters in inappropriate ways, at least on Windows.
ifstream fin("cloud.jpg", ios::binary);
Also, instead of a while loop, you can just read the whole file in one shot:
ostrm << fin.rdbuf();
You shouldn't read the file to a string because it is legal for a jpg to contain values that are 0. However in a string, the value 0 has a special meaning (it's the end of string indicator aka \0). You should instead read the file into a vector. You can do this easily like so:
#include <algorithm>
#include <iostream>
#include <fstream>
#include <vector>
int main(int argc, char* argv[])
{
std::ifstream ifs("C:\\Users\\Borgleader\\Documents\\Rapptz.h");
if(!ifs)
{
return -1;
}
std::vector<char> data = std::vector<char>(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>());
//If you really need it in a string you can initialize it the same way as the vector
std::string data2 = std::string(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>());
std::for_each(data.begin(), data.end(), [](char c) { std::cout << c; });
std::cin.get();
return 0;
}
Try opening the file in binary mode:
ifstream fin("cloud.jpg", std::ios::binary);
At a guess, you were probably trying to read the file on Windows and the 61st character was probably 0x26 -- a control-Z, which (on Windows) will be treated as marking the end of the file.
As far as how to best do the reading, you end up with a choice between simplicity and speed, as demonstrated in a previous answer.
So I have made a program that opens up a text file using ifstream. Now I want to make it so it outputs this file in binary. I have tried ofstream and using .write() but when I do the program crashes. I set it up correctly when using .write() as I have seen online but I haven't seen anyone do it with what I was working with. Anybody have a solution to this? Also, I do not know why 'InputFile' and 'OutputFile' are both highlighted blue like that.
#include <iostream>
#include <fstream>
#include <string>
#include <bitset>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
int main(int argc, char* argv[])
{
if (argc < 2)
{
cout << "Error 1";
return 0;
}
else
{
int WIDTH, HEIGHT;
ifstream InputFile;
InputFile.open(argv[1], ios::in);
ofstream OutputFile;
OutputFile.open("OUTPUT.raw", ios::binary | ios::app);
cout << "Enter Width" << endl;
WIDTH = cin.get();
HEIGHT = WIDTH;
for (int x = 0; x < WIDTH; x++)
{
for (int y = 0; y < HEIGHT; y++)
{
OutputFile.write((char*)InputFile.get(), sizeof(InputFile));
}
}
}
//cout << bitset<8>(txt[i]);
return 0;
};
OutputFile.write((char*)InputFile.get(), sizeof(InputFile));
First, istream::get() extracts one characters from the stream and returns its value casted to an integer. The result is a temporary, which you cast to a pointer to char! It compiles, because the C-style cast basically tells the compiler "shoosh, I know what I'm doing!", but it will certainly do weird things at run-time. You need to get an adress of some object where the value you want to write is stored in, and cast that adress.
The second thing, sizeof(InputFile) returns size of ifstream class that manages the file stream. It's not in any way related to how many data is in the stream's buffer.
If you open a stream in text mode, then the correct way to extract data from it is to use extraction operator (>>). Then it's pretty simple:
std::ifstream in_file("numbers.txt");
std::ofstream out_file("numbers.bin", std::ios::binary);
int i;
while (in_file >> i)
out_file.write(reinterpret_cast<char*>(&i), sizeof(int));
The above snippet will work with an input text file like this: -4 21 1990 5425342 -3432 0 100.
You will have to parse your text file to get int for every string in file and just create a new file and write your binary data with fputc() or fwrite() functions.