Why cfile::read() returns garbage value at the end of file

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Here's my snippet:

CFile cfile_object;
char szSampleText[50];
UINT lBytesRead = cfile_object.Read(szSampleText, 50);

I'm reading text file using above code but it has garbage value at end of file.

Here "szSampleText" has garbage value while debugging. How to use CFile::Read() without
returning garbage value. Pls help!

What I have tried:

CFile cfile_object;
char szSampleText[50];
UINT lBytesRead = cfile_object.Read(szSampleText, 50);

Posted 21-Jan-19 1:54am

rmds

Updated 21-Jan-19 2:31am

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Richard MacCutchan 21-Jan-19 8:06am

You need to check the return value (lBytesRead) to see how much new data was actually received.

[no name] 21-Jan-19 8:12am

+5

rmds 21-Jan-19 8:20am

I don't get it.

rmds 21-Jan-19 8:19am

This is what I get in lBytesRead in debugging
"lBytesRead 44 unsigned int"

rmds 21-Jan-19 8:19am

This is what I get in lBytesRead in debugging
"lBytesRead 44 unsigned int"

Richard MacCutchan 21-Jan-19 8:41am

And? What is that supposed to mean? If you have a problem with your code then you need to provide proper details of the problem. All you have told us is that you are getting "garbage values". But you have not given any detail of what those values are, and why you think they should not be there.

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OriginalGriff · Accepted Answer · 2019-01-21T02:31:00

Solution 1

Quote:
This is what I get in lBytesRead in debugging
"lBytesRead 44 unsigned int"

So what has been read is 44 bytes out of a possible max of 50. So 44 bytes will be transferred to yoru buffer, and the remaining elements will not be affected in any way; their previous content - random according to your snippet - will remain as they were. This may give an impression of "random data at the end" and no terminating null '\0' will be appended. So if you print the array as a string assuming it is a valid null-terminated string, you will get random rubbish after your actual data.

In addition, Read is really intended for binary data, it takes no account of the file content. So check your file with a hex editor and make sure that it contains text, and only text: it if contains binary data, then you will get binary data, which may not be immediately printable! Use the debugger to compare the file content shown in the hex editor with the actual content of your array.

Posted 21-Jan-19 2:31am

OriginalGriff

Comments

rmds 21-Jan-19 12:23pm

Thanks! you're eye opener

OriginalGriff 21-Jan-19 12:34pm

You're welcome!

rmds 21-Jan-19 12:33pm

I also have another doubt. I'm sending file from server to client using CSocket. I'm calling Socketid.Receive() in client end. Where the text file will be received? Here's the snippet.
"Server-end"
ULONGLONG dwLength = sourceFile.GetLength();
char* buffer = new char[(int)dwLength + 1];
buffer[dwLength] = 0;
UINT nActual = sourceFile.Read(buffer, dwLength);
if(DataBytes == SOCKET_ERROR) {
AfxMessageBox(L"Error while sending");
return;
}
nActual = nActual - DataBytes;
}
"Client-End"

char *pBuf =new char [1025];
CString strData;
int iLen;
iLen=m_SocketClient.Receive(pBuf,1024);

After I run this code, I'm not finding any text file in Client Folder.

OriginalGriff 21-Jan-19 12:35pm

Well no ... it won't save it to disk unless you explicitly tell it to!

rmds 21-Jan-19 12:46pm

Is there a way to save the file to drive... instead of CFile::ModeCreate and then write into file? I dont wanna create file and then write into it. Thanks!

Rick York 21-Jan-19 13:40pm

If this is a console application you can have it write to stdout and then redirect that to a file. If it's a GUI app then you will have to open, write, and close the file.

OriginalGriff 21-Jan-19 14:19pm

You can't write to a file without opening it in some fashion, writing the data to it, and saving it.
Even Rick's suggestion does that!