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Write a Byte array to a file

Posted on 2007-11-29
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Last Modified: 2010-04-01
How can i write a byte array,for eg:

BYTE *buf = new BYTE[200];
buf=somedata ;

into a file,for eg "bytedata.dat"

please provide some good eg
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Question by:aslamshikoh1
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Expert Comment

by:jkr
ID: 20375217
The easiest way would be to

#include <stdio.h>

//...


BYTE *buf = new BYTE[200];

//...

FILE* p = fopen(bytedata.dat","wb");

fwrite(buf, 1, 200);

fclose(p);
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Expert Comment

by:jkr
ID: 20375245
Or, more on the C++ side:

#include <fstream>
using namespace std;


BYTE *buf = new BYTE[200];

//..


ofstream os("bytedata.dat", ios_base::out | ios_base::binary);

os.write(buf,200);

os.close();
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Expert Comment

by:jkr
ID: 20375278
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Expert Comment

by:evilrix
ID: 20375459
Don't forget to free your buffer
BYTE *buf = new BYTE[200];
delete [] buf;

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Expert Comment

by:evilrix
ID: 20375461
Also, in C++ consider using std::string instead...
http://msdn2.microsoft.com/en-us/library/syxtdd4f(VS.80).aspx
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Expert Comment

by:evilrix
ID: 20375525
An example using strings and streams...
#include <string>
#include <iostream>
#include <fstream>
 
int main()
{
	// The data we wish to write to file
	std::string sData("Hello world");
 
	// Open the file as a stream (destructor will close for us)
	std::ofstream ofs("c:\\temp\\data.txt");
 
	// If file was opened ok...
	if(ofs.is_open())
	{
		// Write out data to it
		ofs << sData;
 
		// If write error then report it
		if(!ofs.good())
		{
			std::cerr << "Failed to write data" << std::endl;
		}
	}
 
	return 0;
}

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Author Comment

by:aslamshikoh1
ID: 20375878
Ok i got it but i have a continuous stream of bytes to write to a file.Its a thread which has a while loop like this:

while(oEditStreamImpl->isActive_  && --count)
      {
            

            ofstream os("bytedata.dat", ios_base::out | ios_base::binary);
                 os.write(buf,200);
}

os.close()

so how can i append the data to end of the file,like something to do with the file pointer,right now data is getting overwritten.
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Author Comment

by:aslamshikoh1
ID: 20375906
also write(buf,200) complains about not able to accept a byte,i guess a char array is what it accepts,so im just casting it like

write((char*)buf,200)

is it OK to do this
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Accepted Solution

by:
evilrix earned 125 total points
ID: 20376027
Try: -
ofstream os("bytedata.dat", ios_base::binary);
while(oEditStreamImpl->isActive_  && --count)
{
    os.write(reinterpret_cast<char *>(buf),200);
}
os.close();

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Assisted Solution

by:jkr
jkr earned 125 total points
ID: 20376028
>>is it OK to do this

yes, absolutely, since the stream is openend as binary.
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Expert Comment

by:evilrix
ID: 20376077
>> is it OK to do this
Yes, a stream expects a char * but you can cast any pointer type to that as long as you specify correctly the number of chars when writing it out. It helps if you just think of it as writing signed bytes.

NB. a wide stream expects wchar_t *
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Expert Comment

by:Infinity08
ID: 20376145
btw, this :

        BYTE *buf = new BYTE[200];
        buf=somedata ;

creates a memory leak ... you're overwriting the pointer to the allocated 200 bytes with a new value.
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