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File Streaming Problem

General and Gameplay Programming Programming

Started by Bagpuss January 11, 2002 07:44 AM

9 comments, last by Bagpuss 22 years, 3 months ago

Bagpuss

122

Author

January 11, 2002 07:44 AM

Quick question today, I am trying to use a filestream to output data in a binary mode. (Using Windows and MS Vis C++) this does not work, but it does go into the strOP.write instruction

  
	#include <fstream>
	#include <ios.h>
	#include <stdiostr.h>
	#include <fstream.h>

	int nMode = ios::out|ios::binary;

	std::ofstream strOp("C:\\matt.bin",nMode);

	if (strOp.is_open==0)
	{
		AfxMessageBox("Failed to open file ",MB_OK,0);
		failed = TRUE;
	}
	else
	{
		strOp.write("This is a test",14);
		strOp.close();
	}

But this code does. It opens a file as text output

  
	int nMode = ios::out;
	std::ofstream strOp("C:\\matt.bin",nMode);

	if (strOp.is_open==0)
	{
		AfxMessageBox("Failed to open file ",MB_OK,0);
		failed = TRUE;
	}
	else
	{
		strOp.write("This is a test",14);
		strOp.close();
	}

What is wrong and how do I open a file in Binary mode ? TIA, BP.

Anonymous

January 11, 2002 07:51 AM

I always use <Stdio.h> for my file stuff :o).

  FILE *out;//Instead of using \\ you can use /out = fopen("C:/matt.bin","wb");if (out) //Open succesful?{//fwrite(void *,size_t,size_t,FILE*);/*The first size is the size of the data type you''re passing, in this case it''s 1 (sizeof(char)), but you can output an array of ints,shorts,float,etc,etc by using sizeof(type), and then the # of array elements.  I dunno, I hate using filestream''s, standard C is more efficient, and just as simple to read/understand.*/ fwrite("This is a test",1,14,out); fclose(out);}else{ AfxMessageBox("Failed to open file",MB_OK,0); failed = true;}

hewhay

122

January 11, 2002 07:56 AM

do not mix the std headers with common headers
use or not both. try with std::ios::binary

humanity will always be slaved by its ignorance

Enjolras

122

January 11, 2002 08:57 AM

Just out of curiosity, why are you opposed to "mixing the standard and common headers" ?

To answer the question. I have NO flipping idea why this matters, and I suspect its a VC++ bug, but you need to remove the namespace decleration from the beginning of :

std::ofstream

IE

ofstream strOp("C:\\matt.bin",nMode);

I tried your code and it never created the file. I took off the qualifier and it worked like a charm.

It worked fine both with the namespace decleration (std:

and without in ASCII mode.

Nick
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Edited by - enjolras on January 11, 2002 10:15:13 AM

SteveC

122

January 11, 2002 09:47 AM

The likely reason as to why you need to remove the std namespace declaration is because you included some of the headers with .h

the C++ standard library headers should all always be included as #include <fstream> #include <ios> etc.

adding the .h includes older versions of the headers ( such as non-template forms of iostreams ) and does not put things into the std namespace

As to why it is not working when you open in binary mode - a possible explanation is that you can''t really write a string to an iostream in binary mode and expect it to make a human readable file. - especially when you use the raw write() method

you should probably use the insertion operators -

eg

strOp << "This is a test";

which will properly write a string to the output stream.

I suggest looking up some info on iostreams - using inserters/extractors is a primary part of their design - it allows typesafe IO with formatting.

hewhay

122

January 11, 2002 10:18 AM

iostream.h, fstream.h, ios.h, blah...
All belong to an old implemetation of the C++ standard. The newest uses the classes in iostream, fstream, etc. The only (i think) *io*.h that is still the same is iosfwd.h. Even stdio.h turned into cstdio alogn with string.h (cstring), stdlib.h(cstdlib), ctype.h (cctype) because the old c headers are now cheadername and intrudeced into the std namespace.

humanity will always be slaved by its ignorance

pink_daisy

200

January 11, 2002 04:31 PM

sorry, i started this about 7am, and had to leave. It''s now 2:30pm. I''m sure your question has already been answered, but i''ll hit post anyways.

  #include <fstream>using namespace std;int main(){// get a file pointer and open the fileofstream fileOut;//fileOut.open("test.bin", ios::out | ios::in | ios::binary); // used for appendingfileOut.open("test.bin", ios::binary); // delets old file firstchar test[] = "this is a test";fileOut.write((char *)(&test), sizeof(test));fileOut << flush;fileOut.close();return 0;}

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Kylotan

10,510

January 11, 2002 09:44 PM

Yep: you don''t mix use of the ''.h'' extension headers with the headers that lack the ''h''. At best, they won''t work together and will give you compilation or linking errors, or at worst, they still compile fine and yet produce the wrong behaviour, which is what you have here. The ios:: flags you want are included for you when you #include fstream, so you don''t need to include ios anyway. Certainly not ios.h, which is the old library as previously stated.

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Bagpuss

122

Author

January 13, 2002 07:47 AM

OK, thanks for all your input and help !

Bp.

abdulla

164

January 13, 2002 07:57 AM

i''ve had really bad experience with microsoft implementation of iostream, it wouldn''t do tellg, seekg, tellp or seekp properly, and those are simple fundamental things, i prefer C stdio, simply because its small, clean and efficient, it also works off the bat, no pissing around

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