#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
int main(int argc,char *argv){
fstream inout("C:\\Users\\7\\Desktop\\test.txt",ios::in | ios::out | ios::binary);
if (!inout){
cout<<" cannot open input file.\n";
return 1;
}
long e,i,j;
char c1,c2;
e=5;
for (i=0,j=e;i<j;i++,j--){
inout.seekg(i,ios::beg);
inout.get(c1);
inout.seekg(j,ios::beg);
inout.get(c2);
inout.seekp(i,ios::beg);
inout.put(c2);
inout.seekg(j,ios::beg);
inout.put(c1);
}
inout.close();
return 0;
}
why this code writes can't open file
EDIT:
i have made corrections but here is one problem
in test.txt is written such thing
maiko
miyvarxar
shen
me
so it should write
me shen miyvarxar maiko
but it does not write anything
please help
This seems to work for me:
using namespace std;
int main()
{
fstream inout("C:\\Users\\turdfurguson\\Turds\testfile.txt", ios::in | ios::out | ios::binary);
if (inout.good())
cout << "OK!" << endl;
}
Provided you have a "C:\Users\turdfurgson\Turds\testfile.txt" file that is readable and writable.
The code you've provided looks fine.
You may have supplied the wrong path or something like that.
You could also try attempting to open that file in read only mode
and see if that is ok:
std::ifstream in("path", std::ios::binary);
if (!in) {
// fail
}
Related
i tried to open and read an application in binary mode and get 100 characters(For a large file, i did this so that i could read all the characters) in binary mode and then transfer them to new file(in fact, this program will be the same as the previous program, but with a different name ) to find out if it works properly or not
so anyway my source code is:
#include <iostream>
#include <vector>
#include <fstream>
using namespace std;
int main()
{
//Vector of 100 characters initialised to 0
vector<char> ch(100, 0);
ifstream file("example.exe",ios::in|ios::binary);
if (file.is_open())
{
while (file)
{
file.read(ch.data(), 100);
// Get the number of bytes actually read
size_t count = file.gcount();
ch[file.gcount()] = '\0';
//cout << ch.data() << endl;
ofstream output("output.exe", ios::out | ios::binary | ios::app);
output.write(ch.data(), sizeof(100));
output.close();
}
}
file.close();
}
my problem is the output with the correct information is not included and the size is smaller than the original application(example.exe) what is happening?
The line output.write(ch.data(), sizeof(100));
should be replaced with output.write(ch.data(), count);
Since sizeof(100) only returns 4, which is the size in bytes of an integer.
You should also remove the line ch[file.gcount()] = '\0'; since file.gcount() might be out of bound.
I just tested it and this works for me
#include <iostream>
#include <vector>
#include <fstream>
using namespace std;
int main()
{
vector<char> ch(100, 0);
ifstream file("app.exe",ios::in|ios::binary);
if (file.is_open())
{
ofstream output("app_copy.exe", ios::out | ios::binary | ios::trunc);
while (file)
{
file.read(ch.data(), 100);
output.write(ch.data(), file.gcount());
}
output.close();
}
file.close();
}
Notice that ios::app is replaced by ios::trunc, which will delete the content of the file when opening.
I just started working with binary files in C++, and i have successfully written and read a (.bin) file. Here is the code:
#include <iostream>
#include <cstring>
#include <fstream>
using namespace std;
int main()
{
char input[100];
strcpy(input, "This is a string");
fstream file("example.bin", ios::binary | ios::in | ios::out |
ios::trunc);
if(!file.is_open())
{
cerr << "Error opening file.\n";
} else {
for(int i = 0; i<= strlen(input); i++)
{
file.put(input[i]);
}
}
file.seekg(0);
char ch;
while(file.good())
{
file.get(ch);
cout<<ch;
}
}
And this worked. After that, i tried to redesign the code to just read a binary file. The major changes were: changed fstream to be an ifstream(to read), deleted the part with writing into a file. Once the code was ready, i found a file i want to read (eof0.bin). When i used the code, the only thing i got was an empty string. I noticed that the initial size of the file was 37 kilobytes, while after using my program it became 0. I want to know, how my program cleared the data in the binary file?
This is the code that i used to read the file.
#include <iostream>
#include <cstring>
#include <fstream>
using namespace std;
int main()
{
ifstream file("eof0.bin", ios::binary | ios::in | ios::out | ios::trunc);
if(!file.is_open())
{
cerr << "Error opening file.\n";
} else {
// Nothing.
}
file.seekg(0);
char ch;
while(file.good())
{
file.get(ch);
cout<<ch;
}
}
Everything compiles, but using it on a file 37 kilobytes in size gives me a 0 kilobyte file.
You open with an openmode std::ios_base::trunc. From http://en.cppreference.com/w/cpp/io/ios_base/openmode we can see that it
discard[s] the contents of the stream when opening
So just use:
// also dropped ios::out since you only want to read, not write
ifstream file("eof0.bin", ios::binary | ios::in);
Further, this
char ch;
while(file.good())
{
file.get(ch);
cout<<ch;
}
is not an appropriate way to read the file. Think about what happens with an empty file: After opening it, it's "good" (remember, the eofbit is only set when some input operation encounters eof). Then the get fails, leaving ch as it is, thus invoking undefined behavior. Better test on the stream state directly after the input operation:
char ch;
while (file.get(ch)) {
// use ch
}
// optionally distinguish eof and fail cases
For more background on reading files, see Why is iostream::eof inside a loop condition considered wrong?
I have written a program which opens a file then displays line by line its contents (text file)
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main (int argc, char* argv[])
{
string STRING;
ifstream infile;
infile.open(argv[1]);
if (argc != 2)
{
cout << "ERROR.\n";
return 1;
}
if(infile.fail())
{
cout << "ERROR.\n";
return 1;
}
else
{
while(!infile.eof())
{
getline(infile,STRING);
cout<<STRING + "\n";
}
infile.close();
return 0;
}
}
What do I need to add to make the file be read only ?
(infile.open(argv[1]) is where am guessing something goes)
The class ifstream is for reading only so, problem solved. Also, did you really mean to check argc after using argv[1] ?
On the other hand, when you use fstream you need to specify how you want to open the file:
fstream f;
f.open("file", fstream::in | fstream::out); /* Read-write. */
The default mode parameter of open for ifstream class is ios::in. That is
infile.open(argv[1]);
is same as:
infile.open(argv[1], ios::in);
So you are opening the file in read-only mode.
You already open the file for read-only. Your can't write to it if you use ifstream. Even:
infile.rdbuf()->sputc('a');
is guaranteed to fail.
You don't need to do anything as the default value for the openmode is already ios_base::in. So you're already good to go :)
See here for more details: http://en.cppreference.com/w/cpp/io/basic_ifstream/open
I'm trying to open a binary file for writing without erasing the content. But I do not want to write to eof. I want to write to a specific position in file.
Here is a litte example:
ofstream out("test.txt", ios::binary | ios::app);
for(int i = 0; i < 100; i++)
out.put('_');
out.write("Hallo", 5);
out.close();
ofstream out2("test.txt", ios::binary | ios::app);
out2.seekp(10);
out2.write("Welt", 4);
out2.close();
If using app, seek doesn't work. If not using app opening file erases data. Does anybody know an answer?
try the second overload of seekp, which allows you to provide an offset and a direction, this could be begining of file in your case (i.e. ios_base::beg). This of course assumes you know what you are doing and all you want to do is overwrite an existing number of characters.
EDIT: here is fully working example:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
{
ofstream out("test.txt", ios::binary);
for(int i = 0; i < 100; i++)
out.put('_');
out.write("Hallo", 5);
}
{
fstream out2("test.txt", ios::binary | ios::out | ios::in);
out2.seekp(10, ios::beg);
out2.write("Welt", 4);
}
}
When opening with ios::app, it is as if you open a new file that just happened to be attached to an existing file: you can not access the existing file. I'm not sure, because I would do as in Kerrek's answer, but if you really want to try, you probably have to open with "ios::in | ios::out", similar to fopen("test.txt", "rw").
Or as crashmstr points out: ios::out might be enough.
You cannot magically extend the file from the middle. Perhaps easiest to write to a new file: First copy the initial segment, then write your new data, then copy the remaining segment. When all is done, you can overwrite the original file.
According to the specification of fstream here
fstream::open
the ios::app "Sets the stream's position indicator to the end of the stream before EACH output operation." So ios::app doesn't work for replacing, seeks of any sort fail, at least for me.
Just using ios::out does wipe out the file contents preserving only the size, basically turning the file into trash.
ios::in|ios::out turned out as the only working thing for me.
Working Code: This code searches for a string (OLD-STRING) in cout.exe and replaces with a new string (NEW-STRING).
`#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main(int argc, char *argv[])
{
fstream ifs;
ifs.open ("C:\\Users\\user\\Desktop\\cout.exe", fstream::binary | fstream::in | fstream::out);
std::string str((std::istreambuf_iterator<char>(ifs)), std::istreambuf_iterator<char>());
size_t pos = str.find("OLD-STRING");
if (pos != string::npos)
{
cout << "string found at position: " << int(pos) << endl;
ifs.seekp(pos);
ifs.write("NEW-STRING", 10);
}
else
{
cout << "could not find string" << endl;
}
if (ifs.is_open())
ifs.close();
return 0;
}`
I've been all over the ifstream questions here on SO and I'm still having trouble reading a simple text file. I'm working with Visual Studio 2008.
Here's my code:
// CPPFileIO.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <fstream>
#include <conio.h>
#include <iostream>
#include <string>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
ifstream infile;
infile.open("input.txt", ifstream::in);
if (infile.is_open())
{
while (infile.good())
cout << (char) infile.get();
}
else
{
cout << "Unable to open file.";
}
infile.close();
_getch();
return 0;
}
I have confirmed that the input.txt file is in the correct "working directory" by checking the value of argv[0]. The Open method just won't work.
I'm also having trouble debugging- should I not be able to set a watch on infile.good() or infile.is_open()? I keep getting
Error: member function not present.
EDIT: Updated code listing with full code from .CPP file.
UPDATE: The file was NOT in the Current Working Directory. This is the directory where the project file is located. Moved it there and it works when debugging in VS.NET.
Try using the bitwise OR operator when specifying the open mode.
infile.open ("input.txt", ios::ate | ios::in);
The openmode parameter is a bitmask. ios::ate is used to open the file for appending, and ios::in is used to open the file for reading input.
If you just want to read the file, you can probably just use:
infile.open ("input.txt", ios::in);
The default open mode for an ifstream is ios::in, so you can get rid of that altogether now. The following code is working for me using g++.
#include <iostream>
#include <fstream>
#include <cstdio>
using namespace std;
int main(int argc, char** argv) {
ifstream infile;
infile.open ("input.txt");
if (infile)
{
while (infile.good())
cout << (char) infile.get();
}
else
{
cout << "Unable to open file.";
}
infile.close();
getchar();
return 0;
}
Sometimes Visual Studio puts your exe file away from your source code. By default VS may only look for the file starting from your exe file. This process is a simple step for getting the input txt file from the same directory as your source code. Should you not want to fix your IDE setup.
using namespace std;
ifstream infile;
string path = __FILE__; //gets source code path, include file name
path = path.substr(0,1+path.find_last_of('\\')); //removes file name
path+= "input.txt"; //adds input file to path
infile.open(path);
Hopefully this helps other people for a quick solution. It took me a while to find this setup myself.
I've found two problems in your code:
a) syntax error in "ios::ate || ios::in" => should be "ios::ate | ios::in"
b) "ios::ate" sets the cursor to the end of file - so you get nothing when you start reading
So just remove "ios::ate" and you are fine :)
ciao,
Chris
infile.open ("input.txt", ios::ate || ios::in);
|| is the logical or operator, not the bitwise operator (as Bill The Lizzard said).
so i guess you are doing the equivalent to:
infile.open ("input.txt", true);
(assuming neither ios::ate or ios::in are 0)
Try using:
ifstream fStm("input.txt", ios::ate | ios::in);
I'm also having trouble debugging- should I not be able to set a watch on "infile.good()" or "infile.is_open()"? I keep getting "Error: member function not present."
and the proper includes:
#include <fstream>
etc.
If you use the default Vs code setup, place the text file that you want to read from in the same folder as your executable, I know it is not pretty but yeah it works