Programming Forums > Application Development > C++

Lesliect6 · Aug 24th, 2007, 5:56 PM

Hello,

I have been trying to figure this out myself, but without success. I have recently started wxWidgets programming, and I was trying to find a way to write a string to an existing file. The name of the file is a string which I extract from a textBox. Now, in wxWidgets, the string type contained in a textBox is a wxString, so I cannot use it with the standard ofstream. There is a wxFile class, but the Write() method produces a weird error. Here is the code and the error message :

(Toggle Plain Text)

wxFile *file_to_write_to = new wxFile(WxEdit1->GetLineText(1));
if (!file_to_write_to->IsOpened()) // if error while opening file
    ErrorDialog->ShowModal();
else // if file could be opened
{
    file_to_write_to->Seek(pos); // go to a given position in the file
    wxString x="string to write";
    file_to_write_to->Write(x);
    delete file_to_write_to;
}

The program compiles correctly, but when I try to execute this code, I get :

(Toggle Plain Text)

can't write to file descriptor 3 (error 5: access refused)

Now I am pretty sure I have access to everything on my computer, I am in Administrator mode, the file I am opening is just an example file created using Notepad, "example.txt", there are no writing restrictions, no read-only, everything is fine. I get this error with every other file too. I narrowed down the problem and what I can be sure of is that the file IS opened successfully. The problem occurs after the "delete file_to_write_to;", even if I change it to "file_to_write_to->Close();". However, nothing is written to the file.

If there is an easier way to write to a file, please let me know, or help me out with this code, which appears to me to be logical.

Thank you,

Leslie

DaWei · Aug 24th, 2007, 6:10 PM

You can get the C string with the .c_str () method. Just pass that as the name of the file when you call wxFile::Open. You WILL need to open the file before writing to it.

Lesliect6 · Aug 25th, 2007, 6:23 AM

Thank you DaWei, but the problem still persists. I did exactly as you said, and now I get the error :

(Toggle Plain Text)

can't write to file descriptor 8 (error 9: wrong file descriptor)

The modified code is as follows :

(Toggle Plain Text)

wxFile *file_to_write_to = new wxFile(WxEdit1->GetLineText(0).c_str());
if (!file_to_write_to->IsOpened()) // if error while opening file
    ErrorDialog->ShowModal();
else // if file could be opened
{
    file_to_write_to->Seek(pos); // go to a given position in the file
    wxString x="string to write";
    file_to_write_to->Write(x);
    delete file_to_write_to;
}

The program does not show the ErrorDialog, which means the file is opened correctly. However, nothing is written to it.

Thank you,

Leslie

dr.p · Aug 25th, 2007, 6:43 AM

You need to use wxFile::write as the second parameter to your wxFile constructor call, since the file is opened in read mode by default.

e.g.

(Toggle Plain Text)

wxFile *file_to_write_to = new wxFile(WxEdit1->GetLineText(0).c_str(), wxFile::write);

Your error message probably changed, by the way, because you didn't explicitly identify your c_str as a const char *. It looks like it's being interpreted as an integer, so you're actually calling the secondary constructor, which requires an integer value that identifies the file descriptor.

Check out the wxFile class in the widget docs for more details. You can download the docs from the wxWidget web site in a number of formats to have handy.

DaWei · Aug 25th, 2007, 7:24 AM

Absolutely. If you only give a single value to the constructor, without casting, it will be interpreted as a file descriptor. If you add the second argument, open mode, the first argument will be interpreted as a const char * without the cast.

As dr.p says, a visit to the documentation is in order.

Lesliect6 · Aug 25th, 2007, 8:33 AM

Thank you very much! Now it works! I should have read the documentation more closely. This was a valuable lesson.

Leslie

Aug 24th, 2007, 5:56 PM	#1
Lesliect6 Programmer Join Date: Aug 2005 Posts: 68 Rep Power: 3	wxFile problem Hello, I have been trying to figure this out myself, but without success. I have recently started wxWidgets programming, and I was trying to find a way to write a string to an existing file. The name of the file is a string which I extract from a textBox. Now, in wxWidgets, the string type contained in a textBox is a wxString, so I cannot use it with the standard ofstream. There is a wxFile class, but the Write() method produces a weird error. Here is the code and the error message : (Toggle Plain Text) wxFile file_to_write_to = new wxFile(WxEdit1->GetLineText(1)); if (!file_to_write_to->IsOpened()) // if error while opening file ErrorDialog->ShowModal(); else // if file could be opened { file_to_write_to->Seek(pos); // go to a given position in the file wxString x="string to write"; file_to_write_to->Write(x); delete file_to_write_to; } wxFile file_to_write_to = new wxFile(WxEdit1->GetLineText(1)); if (!file_to_write_to->IsOpened()) // if error while opening file ErrorDialog->ShowModal(); else // if file could be opened { file_to_write_to->Seek(pos); // go to a given position in the file wxString x="string to write"; file_to_write_to->Write(x); delete file_to_write_to; } The program compiles correctly, but when I try to execute this code, I get : (Toggle Plain Text) can't write to file descriptor 3 (error 5: access refused) can't write to file descriptor 3 (error 5: access refused) Now I am pretty sure I have access to everything on my computer, I am in Administrator mode, the file I am opening is just an example file created using Notepad, "example.txt", there are no writing restrictions, no read-only, everything is fine. I get this error with every other file too. I narrowed down the problem and what I can be sure of is that the file IS opened successfully. The problem occurs after the "delete file_to_write_to;", even if I change it to "file_to_write_to->Close();". However, nothing is written to the file. If there is an easier way to write to a file, please let me know, or help me out with this code, which appears to me to be logical. Thank you, Leslie

Aug 24th, 2007, 6:10 PM	#2
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	You can get the C string with the .c_str () method. Just pass that as the name of the file when you call wxFile::Open. You WILL need to open the file before writing to it. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Aug 25th, 2007, 6:23 AM	#3
Lesliect6 Programmer Join Date: Aug 2005 Posts: 68 Rep Power: 3	Thank you DaWei, but the problem still persists. I did exactly as you said, and now I get the error : (Toggle Plain Text) can't write to file descriptor 8 (error 9: wrong file descriptor) can't write to file descriptor 8 (error 9: wrong file descriptor) The modified code is as follows : (Toggle Plain Text) wxFile file_to_write_to = new wxFile(WxEdit1->GetLineText(0).c_str()); if (!file_to_write_to->IsOpened()) // if error while opening file ErrorDialog->ShowModal(); else // if file could be opened { file_to_write_to->Seek(pos); // go to a given position in the file wxString x="string to write"; file_to_write_to->Write(x); delete file_to_write_to; } wxFile file_to_write_to = new wxFile(WxEdit1->GetLineText(0).c_str()); if (!file_to_write_to->IsOpened()) // if error while opening file ErrorDialog->ShowModal(); else // if file could be opened { file_to_write_to->Seek(pos); // go to a given position in the file wxString x="string to write"; file_to_write_to->Write(x); delete file_to_write_to; } The program does not show the ErrorDialog, which means the file is opened correctly. However, nothing is written to it. Thank you, Leslie

Aug 25th, 2007, 6:43 AM	#4
dr.p Programmer Join Date: Feb 2006 Location: Ohio Posts: 93 Rep Power: 3	You need to use wxFile::write as the second parameter to your wxFile constructor call, since the file is opened in read mode by default. e.g. (Toggle Plain Text) wxFile file_to_write_to = new wxFile(WxEdit1->GetLineText(0).c_str(), wxFile::write); wxFile file_to_write_to = new wxFile(WxEdit1->GetLineText(0).c_str(), wxFile::write); Your error message probably changed, by the way, because you didn't explicitly identify your c_str as a const char *. It looks like it's being interpreted as an integer, so you're actually calling the secondary constructor, which requires an integer value that identifies the file descriptor. Check out the wxFile class in the widget docs for more details. You can download the docs from the wxWidget web site in a number of formats to have handy. __________________ Neeley.org

Aug 25th, 2007, 7:24 AM	#5
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Absolutely. If you only give a single value to the constructor, without casting, it will be interpreted as a file descriptor. If you add the second argument, open mode, the first argument will be interpreted as a const char * without the cast. As dr.p says, a visit to the documentation is in order. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Aug 25th, 2007, 8:33 AM	#6
Lesliect6 Programmer Join Date: Aug 2005 Posts: 68 Rep Power: 3	Thank you very much! Now it works! I should have read the documentation more closely. This was a valuable lesson. Leslie

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Programming Forums > Application Development > C++

wxFile problem