How do I make " fstream " to accept ALL characters?

Question

0.00/5 (No votes)

See more:

The attached code works only when "test.txt" is used as name of the file.
When ""test_1.txt" is used it fails to create / open the file.
Of course it does not work when REAL file name is used.
Obviously I need the real Mc Coy to work, but so far it fails just testing it.

//#define MERGE_1 "/media/z/DEV_COPY_LABEL/ECLIPSE_FOLDER/2019-12/Eclipse_2019_12/eclipse/Workspace_2019_12/RPI_BT_LIB_ARM/MODULE/M_ARM_SOCKET/CARMSOCKET.h"
#define MERGE_1  "test_1.txt"
#define MERGE_1  "test.txt"
	std::string str(MERGE_1);
	char *cstr = new char[str.length() + 1];
	std::strcpy(cstr, str.c_str());
	cout << "cstr " << +cstr << endl;
	fstream fs;
	fs.open(cstr);
	perror_cpp("File state ");
	cout << " Merged file created OK " << endl;

What I have tried:

Flowed instruction to use c_str and it does not work with anything but alpha characters.

Posted 31-Jan-20 5:15am

Vaclav_

Updated 1-Feb-20 7:44am

Add a Solution

3 solutions

Solution 1

Works fine for me. But why are you copying from a string to a char array? All you need is:

fs.open(str); // fstream methods can handle string variables

Also the str.c_str() will handle all characters in the ASCII set: alpha, numeric, special etc. So, whatever problem you are seeing is not clear from the above code.

Posted 31-Jan-20 5:53am

Richard MacCutchan

Comments

Vaclav_ 1-Feb-20 13:48pm

I have tried both char and string - failed same way.

Richard MacCutchan 2-Feb-20 3:43am

It appears that if you do not specify ios_base::out in the open call, the library expects the file to exist already.

Solution 2

At a guess, it's a permissions problem.
You don't specify a path, which means it will try to open or create a file in eth current folder - which for an installed executable will be the application installation folder. On many systems (including Windows) those are by default write protected to reduce virus activity.

Try specifying your file with an explicit absolute path to a "safe" folder and it should work.

Posted 31-Jan-20 5:59am

OriginalGriff

Comments

Vaclav_ 31-Jan-20 12:48pm

Why would different name format behave this way ?

OriginalGriff 31-Jan-20 14:01pm

it probably isn't: it may be that the folder you are working in doesn't have create file permission, or the file may be in use. The first thing to do is to find out exactly what is going on, and for that you need to explicitly specify the folder, and start checking what is happening.
If I try it code, it works - just as I'd expect it to - so it's something specific to your environment or how your app is working that I can't duplicate.

Vaclav_ 31-Jan-20 14:17pm

To "find out what is going on" comment is superfluous. Not really helpful...As far as I remember "open" creates a file IF it does not exist then opens it for whatever mode is specified or in case of stream by the actual "command".
The file location in this case is immaterial, perhaps I will get a different error if file cannot be created "in folder". ( I'll will select non existent folder next ) I am trying to debug this in some logical way by altering analysing the ONLY thing which is changing - the file name.

Here is my latest

ofstream file_1;
file_1.open("file_1.txt"); //open a file
if (file_1.is_open())
cout << "open " << endl;
else
cout << "closed " << endl;

socket.perror_cpp("File 1 state ");
file_1 << "Hello file\n" << 75; //write to it
file_1.close(); //close it

fstream file_2;
file_2.open("file_2.txt"); //open a file
if (file_2.is_open())
cout << "open " << endl;
else
cout << "closed " << endl;
socket.perror_cpp("File 2 state ");
file_2 << "Hello file\n" << 75; //write to it
file_2.close(); //close it

The first "open" works, the second fails - consistently.

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Vaclav_ · Accepted Answer · 2020-02-01T07:45:00

C++

<a href="http://www.cplusplus.com/reference/fstream/fstream/open/">fstream::open - C++ Reference</a>[<a href="http://www.cplusplus.com/reference/fstream/fstream/open/" target="_blank" title="New Window">^</a>]

From the above reference and its example (attached) it looks as fstream despite being advertised as "input / output"  still needs in/ out parameters. 

I am now successfully   using ifstream and ofstream. 
(May try plain fstream with  i/o parameters later )  

PS I woudl even question the necessity of usage of std::(fstream)  in the example. 

// fstream::open / fstream::close
#include <fstream>      // std::fstream

int main () {

  std::fstream fs;
  fs.open ("test.txt", std::fstream::in | std::fstream::out | std::fstream::app);
  fs << " more lorem ipsum";
  fs.close();
  return 0;
}