Read lines of text file one by one with metro apps

Question

Hello

Iam new to developing metro style apps.

Im trying to develop a C++ app that reads a text file. It reads a single line of text and then displays it in a listbox one line at a time.

But i fail to understand how to read a single line. My app is reading the entire file at once.

The code is as follows:

void metro::MainPage::ReadButton_Click(Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
{
 

StorageFolder^ documentsFolder = KnownFolders::DocumentsLibrary;
    auto fileOperation = documentsFolder->GetFileAsync("sample.txt");
    MainPage^ page = this;
    fileOperation->Completed = ref new AsyncOperationCompletedHandler<StorageFile^>([page](IAsyncOperation<StorageFile^>^ operation)
    {
        if (operation->Status == AsyncStatus::Completed)
        {
            // Get the returned file and attempt to open it for a read operation
            StorageFile^ storagefileSample = operation->GetResults();
            auto openOperation = storagefileSample->OpenAsync(FileAccessMode::Read);
            openOperation->Completed = ref new AsyncOperationCompletedHandler<IRandomAccessStream^>([page](IAsyncOperation<IRandomAccessStream^>^ operation)
            {
                if (operation->Status == AsyncStatus::Completed)
                {
                    // Create a DataReader to read the opened file's contents
                    IRandomAccessStream^ stream = operation->GetResults();
                    DataReader^ dataReader = ref new DataReader(stream->GetInputStreamAt(0));

                    // Load in the full stream size
                    auto readOperation = dataReader->LoadAsync(stream->Size);
                    readOperation->Completed = ref new AsyncOperationCompletedHandler<unsigned int>([page, dataReader](IAsyncOperation<unsigned int>^ operation)
                    {
                        // Read the loaded string and display it in the output textblock
                        page->TextBlock->Text = dataReader->ReadString(operation->GetResults());
                    });
                    readOperation->Start();
                }
            });
            openOperation->Start();
        }
        else
        {
            page->TextBlock->Text = "The file sample.txt does not exist.";
        }
    });
    fileOperation->Start();
}

Please help.

Thanks.

Answer 1

Hi ashi1812,

There is no direct line-by-line reading mode. You will have to read the lines in and break them at the newline yourself.

--Rob

Answer 2

How can I do that exactly?

---

Regards, Ashi

Answer 3

Hi Ashi,

If your not too familiar with C++ string manipulation, you may find C# has some simple ways to accomplish this task as well. Here's a snippet that you can add into to the C++ File Access sample to accomplish your task. You need the #includes as well.

#include <windows.h>
#include <wchar.h>

//paste this into the section containing the line that updates
// the TextBlock: page->TextBlock->Text = dataReader->ReadString(operation->GetResults());
 
//Get the Platform::String
auto s = dataReader->ReadString(operation->GetResults());
//Get the wchar_t
auto s2 = s->Data();
					 				 
//Make a copy of the string to avoid overwriting the original 
size_t nlen;
nlen = (wcslen(s2))+1;
wchar_t* tokenIn = new wchar_t[nlen];
wcscpy_s(tokenIn,nlen,s2); 
wchar_t* tokenOut = NULL;
wchar_t delim[] = L"\r\n";
//get the first 'line' up to a CRLF
tokenIn = wcstok_s( tokenIn, delim, &tokenOut );
//Loop to read each subsequent line
while ( tokenIn != NULL )
{
	OutputDebugString( tokenIn );
	tokenIn = wcstok_s( NULL, delim, &tokenOut);
	OutputDebugString( L"-\n-" );
}
delete [] tokenIn;</wchar.h></windows.h>

Thanks,

-David

Answer 4

Hey David,

Thanks for your reply but the code snippet that you have told me to add is still giving errors:

1 . errno_t wcscpy_s(wchar_t *,rsize_t,const wchar_t *)' : cannot convert parameter 3 from 'int' to 'const wchar_t * in the line :

wcscpy_s(tokenIn,nlen,s2);

2. 'wcslen' : cannot convert parameter 1 from 'int' to 'const wchar_t * in the line:

nlen = (wcslen(s2))+1;

3. 'Platform::String::Data': function call missing argument list; use '&Platform::String::Data' to create a pointer to member in the line :

auto ws = _str->Data;

4. 's2': cannot be used before it is initialized in the line :

wcscpy_s(tokenIn,nlen,s2);

Kindly help me with the solution.

---

Regards, Ashi

Answer 5

Hi all,

I've worked upon the solution by using wstrings.

And it's working fine now.

Thanks a lot for your help. :)

---

Regards, Ashi