std::fstream::seekp( ... std::ios::end )

[mathieu]

Hi there,

I think I misunderstood the purpose of std::fstream::seekp. I would
like to append data at the end of a file. So I wrote the following
piece of code (*).

It prints '0' in my console, which means the call to seekp(0,
std::ios::end) did not seek to the end of the file. How am I supposed
to do that in a portable way ? (no such thing as std::ios::app)

Thanks,

#include <fstream>
#include <iostream>

int main()
{
const unsigned int len = 512;
char buffer1[len] = {};
char buffer2[len] = {};
{
std:fstream of( "dummy.raw", std::ios::binary );
of.write( buffer1, len );
of.close();
}

{
std:fstream of( "dummy.raw", std::ios::binary );
of.seekp( 0, std::ios::end );
std::cout << of.tellp() << std::endl;
of.write( buffer2, len );
of.close();
}

}

 

[Bo Persson]

Hi there,

I think I misunderstood the purpose of std::fstream::seekp. I would
like to append data at the end of a file. So I wrote the following
piece of code (*).

It prints '0' in my console, which means the call to seekp(0,
std::ios::end) did not seek to the end of the file. How am I
supposed to do that in a portable way ? (no such thing as
std::ios::app)

Thanks,

#include <fstream>
#include <iostream>

int main()
{
const unsigned int len = 512;
char buffer1[len] = {};
char buffer2[len] = {};
{
std:fstream of( "dummy.raw", std::ios::binary );
of.write( buffer1, len );
of.close();
}

{
std:fstream of( "dummy.raw", std::ios::binary );

This opens/creates a new file, as the default for out-files is
std::ios::trunc. You need to make this std::ios::binary|std::ios::app
to append to the existing file.

 

[mathieu]

Hi there,

I think I misunderstood the purpose of std::fstream::seekp. I would
like to append data at the end of a file. So I wrote the following
piece of code (*).

It prints '0' in my console, which means the call to seekp(0,
std::ios::end) did not seek to the end of the file. How am I
supposed to do that in a portable way ? (no such thing as
std::ios::app)

#include <fstream>
#include <iostream>

int main()
{
const unsigned int len = 512;
char buffer1[len] = {};
char buffer2[len] = {};
{
std:fstream of( "dummy.raw", std::ios::binary );
of.write( buffer1, len );
of.close();
}

{
std:fstream of( "dummy.raw", std::ios::binary );

This opens/creates a new file, as the default for out-files is
std::ios::trunc. You need to make this std::ios::binary|std::ios::app
to append to the existing file.

Thanks. For some reason I was convinced that std::ios::app was not
portable...

Sorry for the noise.