Binary output to file w/C++ ??
Zack Moore
Can anybody tell me if there is a 'nice' and 'C++' way of reading and
writing a float from a file in binary format?
I now realize that
OutFile << Myfloat;
just outputs the text equivalent of the value stored in Myfloat.
Currently I'm using a union and writing the 4 bytes as unsigned char's
one at a time, but there has to be a better way.
Thanks
--
Zack Moore-
"Feel free to use it, but don't give me credit -'Anonymous Cynic'
should suffice. I don't want to piss off half the planet - some
of them may be the people who make gasoline, bread, and electricity."
-[Request to quote an Anonymous Cynic]
Ramón Jiménez
Zack Moore wrote in message <66femn$q...@mtinsc02.worldnet.att.net>...
>Can anybody tell me if there is a 'nice' and 'C++' way of reading and
>writing a float from a file in binary format?
Ramón Jiménez:
Use functions fopen() and fprintf(), like this:
FILE *fp; /*pointer to file*/
fp=fopen("OutFile", "b"); /*OutFile is a filename, b*/
/* tells C++ file is binary*/
fprintf(fp, "%f", Myfloat'); /* Write MyFloat to bin file OutText
Pete Becker
Zack Moore wrote:
>
> Can anybody tell me if there is a 'nice' and 'C++' way of reading and
> writing a float from a file in binary format?
>
>
> OutFile << Myfloat;
>
> just outputs the text equivalent of the value stored in Myfloat.
>
> Currently I'm using a union and writing the 4 bytes as unsigned char's
> one at a time, but there has to be a better way.
cout.write(&f,sizeof(f));
R124c4u2
Zack Moore <tmo...@mail.dodge.public.lib.ga.us> writres:
-----------
When you use << you specify a binary to ASCII conversion. Use
ofstream::write() and ifstream::read() instead.
michael j tobler
the person said "C++" way of doing things,
the example you gave is "C".
do this:
float myfloat ;
ofstream out( "file.txt", ios::out ) ;
out.write( (char *)&myfloat, sizeof(float) ) ;
out.close( ) ;
ifstream in( "file.txt", ios::in ) ;
in.read( (char *)&myfloat, sizeof(float) ) ;
in.close( ) :
--
blue skies
michael j. tobler, mailto:mjto...@NOSPAMix.netcom.com
(Remove NOSPAM in return address if replying by email)
Ramón Jiménez wrote:
> Zack Moore wrote in message <66femn$q...@mtinsc02.worldnet.att.net>...
> >Can anybody tell me if there is a 'nice' and 'C++' way of reading and
> >writing a float from a file in binary format?
>
Slawomir Marczynski
: Zack Moore wrote:
: >
: > Can anybody tell me if there is a 'nice' and 'C++' way of reading and
: > writing a float from a file in binary format?
Define an _binary_ i/o streams (derived from "normal" istream and ostream),
and operator << (binary_ostream& osb, float value) etc. ;)
--
Slawomir Marczynski (Mr)
Institute of Physics, Technical University of Szczecin
Al. Piastow 48/49, 70-310 Szczecin, Poland
sla...@arcadia.inter.tuniv.szczecin.pl, tel:+(048-91)-494056
Michael J. Tobler
This is WAY overboard ... the way to
do is with existing classes and their
respective member functions. Please see
my other post within this thread for the answer.
--
blue skies
michael j. tobler, mailto:mto...@no-spam-ibm.net
(Remove the "no-spam-" in return address)
Michael Benzinger
Slawomir,
You need to be careful with this. Yes, you can derive a class from
istream and ostream, but this does create one problem. Since the
operator<< and operator>> functions are not declared virtual in
ostream and istream, the following will not quite do what you think:
class MyClass
{
public:
...
friend ostream&
operator<<(ostream& os, const MyClass& myClass)
{
os << intMem;
}
private:
int intMem;
};
...
int
main()
{
binary_ostream bos("somefile.dat");
MyClass anInst;
bos << anInstr; // Unfortunately, this calls ostream::operator<<
// not the binary_ostream<<!!
return(0);
}
What function gets called???
Mike Benzinger
On 10 Dec 97 12:15:08 GMT, sla...@arcadia.tuniv.szczecin.pl (Slawomir
Robert P. Ruth
>>: Zack Moore wrote:
>>: >
>>: > Can anybody tell me if there is a 'nice' and 'C++' way of reading and
>>: > writing a float from a file in binary format?
>>
I may have missed something really critical here but, is there a reason that
you cant use the binary flag when you open the file?
file.open("myfile.dat,ios::out|ios::binary);
???
Michael Benzinger
Robert,
He wanted a "C++" way, i.e. "cout << text" way of doing things. Let's
take a look at the following program:
#include <fstream>
int
main()
{
std::ofstream file("testit.bin", std::ios_base::out |
std::ios_base::binary);
int x = 0x01020304;
file << x;
return( 0 );
}
This small program produces the following results in testit.bin:
Offset 0 1 2 3 4 5 6 7 8 9 A B C D E F ASCII
------ -------- -------- -------- -------- -------------
000000 31363930 39303630 16909060
This is not exactly the desired results. As you can see, the values
was still output in ASCII format. The only standard, out-of-the-box,
C++ way to truly write binary data is to use the 'write' function as
follows:
#include <fstream>
int
main()
{
std::ofstream file("testit.bin", std::ios_base::out |
std::ios_base::binary);
int x = 0x01020304;
file.write(reinterpret_cast<char*>(&x), sizeof(x));
return( 0 );
}
This produces the correct results:
Offset 0 1 2 3 4 5 6 7 8 9 A B C D E F ASCII
------ -------- -------- -------- -------- -------------
000000 04030201 ····
NB: The PC uses little-endian byte order, hence the order of the bytes
is backwards.
Mike Benzinger
Jim Ragsdale
How about something like:
#include <fstream.h>
main()
{
float num;
fstream f1("mydata.bin",ios::in|ios::binary);
if( !f1 )
{
cerr << "NO Way Jose" << endl;
return 1;
}
f1.read( &num, sizeof( float ) );
}
Michael J. Tobler <mto...@ibm.net> wrote in article
<348EA12C...@ibm.net>...
> This is WAY overboard ... the way to
> do is with existing classes and their
> respective member functions. Please see
> my other post within this thread for the answer.
> --
> blue skies
> michael j. tobler, mailto:mto...@no-spam-ibm.net
> (Remove the "no-spam-" in return address)
>
> Slawomir Marczynski wrote:
>
> > : Zack Moore wrote:
> > : >
> > : > Can anybody tell me if there is a 'nice' and 'C++' way of reading
and
> > : > writing a float from a file in binary format?
> >
> > Define an _binary_ i/o streams (derived from "normal" istream and
ostream),
> > and operator << (binary_ostream& osb, float value) etc. ;)
> >