C / C++ / MFC

26-Jun-06 18:34

Hi all,
Im creating a .dll using ATL. Recently I have got to add the file operation part to it but as soon as I did it, it started to throw error saying :

" Drawing Assertion failed
Program : c:\windows........
File : fprintf.c
Line :55
Expression : (str!= NULL)
.................. "

This is the part of code which I'm using. It works well as far as I'll keep
fprintf(......);
statement away. But as soon as I included that its throwing error.

<br />
STDMETHODIMP CYourClass::YourATLMethod(BSTR Filepath, BSTR* ReturnString)<br />
{<br />
	_bstr_t LbstrFilepath = Filepath;<br />
		<br />
	XMP_VersionInfo version;<br />
	SXMPMeta::GetVersionInfo ( &version );<br />
	FILE * sLogFile=fopen( "XMPLog.txt", "wb" ); ;<br />
	fprintf ( sLogFile, "Version : %s\n" , version.message ); //here it is throwing errror<br />

please guide me. where and why it is throwing error. What I'm supposed to get rid of this.

Regards,
Arun

David Crow28-Jun-06 5:48

28-Jun-06 5:48

Is sLogFile a valid file pointer? Per the assertion, it is NULL.

What type is version.message?

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

agarunk28-Jun-06 6:26

28-Jun-06 6:26

As per me yes it is. Is there something I need to takecare about that??? Its just a File pointer. Its creating empty file but while coming to "fprintf" it'll throw the error.

version.message is a string.
I have got lots of "fprintf" statement in the module and I checked with all of them one by one its throwing the same error as above.

I'm creatin .dll using ATL in VS 2005.

Regards,
Arun

David Crow28-Jun-06 6:36

28-Jun-06 6:36

agarunk wrote:
version.message is a string.

Then you should probably be using the c_str() method.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

agarunk28-Jun-06 19:16

28-Jun-06 19:16

No I'm not making use of c_str().

Please let me know if it is required to take someother way to get this thing done. If possible with a sample piece of code.

Thanking you
Arun

Jörgen Sigvardsson28-Jun-06 22:08

Jörgen Sigvardsson

28-Jun-06 22:08

The %s directive makes printf() and friends expect a string pointer on the stack. If you pass an object, such as std::string, you'll give it "garbage". If you give it a pointer to the internal string buffer instead, it'll work.

std::string str;
const char* pInternalBuffer = str.c_str();
printf("A string: %s\n", pInternalBuffer);

agarunk29-Jun-06 4:11

29-Jun-06 4:11

Thanks. I tried it but didnt solve the problem. I refered in some other atricles and I think it might happening because of default debugging output directory.

What do you think???

David Crow29-Jun-06 2:37

29-Jun-06 2:37

Have you tried:

fprintf(sLogFile, "Version : %s\n", version.message.c_str());

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

agarunk29-Jun-06 3:50

29-Jun-06 3:50

Thanks. I tried that too but didn't work either.

David Crow29-Jun-06 4:10

29-Jun-06 4:10

The problem, as I mentioned here, is that the FILE* passed to fprintf() is NULL. That's what the assertion is telling you.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

agarunk29-Jun-06 4:14

29-Jun-06 4:14

But it is creating the file in the "fopen" statement.

Ok incase as you said if it is doing so then what is the solution for that. What I'm supposed to do on that case.

David Crow29-Jun-06 4:25

29-Jun-06 4:25

agarunk wrote:
What I'm supposed to do on that case.

I'm out of ideas at this point. You might try setting a breakpoint on the fprintf() statement and verify the value of sLogFile.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

agarunk29-Jun-06 5:16

29-Jun-06 5:16

I'm writing dll and using it in C# so I cant put the break point. That is main problem to trace out.

David Crow29-Jun-06 5:39

29-Jun-06 5:39

At a minimum:

FILE *sLogFile = fopen("XMPLog.txt", "wb");
if (sLogFile != NULL)
{
    fprintf(sLogFile, "Version : %s\n", version.message.c_str()); 
    fclose(sLogFile);
}
else
    MessageBox(...);

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

Jörgen Sigvardsson28-Jun-06 14:14

Jörgen Sigvardsson

28-Jun-06 14:14

I agree with David's suggestion. Passing C++ as a "optional" parameter yeilds undefined behaviour. With CStrings, you can do this, and I bet Microsoft engineers did some tweaking to make that work. I don't know about std::string, but chances are that they are not crafted in such a way that they will work with printf()-like functions...

--
100% natural. No superstitious additives.

agarunk28-Jun-06 19:29