type cast from float to unsigned char*

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The problem that i m getting in this code is when i try to call WriteHeadAndBuffer(kwdId,sizeof(float),(unsigned char*)&f);
in the below code i am not getting correct value(Don't know what it is unicode or garbage) after type cast (unsigned char*)&f.

Is is possible to type cast float to unsigned char* like this...
I am using vs2008.

C

void CQ3DStreamFile::Write(const unsigned long kwdId,const char* keyword,float f)
{
    if (!CheckStream(kOpenedWrite))
        return;

    if (m_Binary)
    {
        WriteHeadAndBuffer(kwdId,sizeof(float),(unsigned char*)&f);
    }
    else
    {
        doWriteIndent();
        fprintf(m_File,"%s\t%s\n",keyword,STRFLOAT(f));
    }
}

[Modified: added code formatting]

Posted 12-Mar-10 8:19am

HardikVC

Updated 12-Mar-10 10:10am

William Winner

v2

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Avi Berger · Answer 1 · 2010-03-12T09:39:00

If I am understanding your intent correctly, you are misunderstanding type casts and what they do. Your variable f contains a binary representation of a floating point number. You are then casting the address of that variable from float * to char *. This does nothing whatsoever to the contents of f. You now have a pointer that you have demanded that the compiler consider a pointer to char that points to nothing of the sort.

Evidently, what you want is a character representation of the value in f. You have no such thing in your code at present. Neither a C or a C++ cast operator is relevant to creating such a thing.

If I am misunderstanding what you are trying to do, please clarify your question.

There are a number of things around that can be used to do this. Some posibilites that you might look at: CString::Format()[^], sprintf()[^], boost::lexical_cast[^], and std::ostringstream which can be used similarly to std::cout. An article that discusses these is here[^].

Most of these work with chars and not unsigned chars, so you may need a cast from char * to unsigned char *. Also what CString will give you is a const char *.

Note: I have been assuming here that you are not using a unicode build and do not have to worry about conversions to/from a unicode encoding.

Eugen Podsypalnikov · Answer 2 · 2010-03-12T10:00:00

Solution 2

I guess, you want to perform a binary dump of a float,

but the writing does probably finish
at the first 0-byte of the floats content... :)

Could you post the implementation of WriteHeadAndBuffer(..) ?

Posted 12-Mar-10 10:00am

Eugen Podsypalnikov