CODEWITHSUNDEEP
c++io
vdsf
vdsf

Reputation: 1618

Writing std::ostringstream to file without copying?

Given a function that takes an output stringstream as an argument:

void Foo(const std::ostringstream& _oss);

Is there any way of writing the stream buffer to a file WITHOUT having to call str() ?

I want to avoid copying the buffer (which str() does).

void Foo(const std::ostringstream& _oss);
{
  std::ofstream f("foo.bin");

  //WANT: write _oss to f without copying the buffer?
}

Upvotes: 3

Views: 3570

Answers (2)

Puppy
Puppy

Reputation: 146910

You can't write it to file without copying- because that's what writing to a file does, it copies it out of memory and on to the disk.

Of course, if you want to get technical about this, you could utilize a memory mapped file.

Upvotes: 0

sbi
sbi

Reputation: 224029

There's an operator<<() taking a stream buffer: 

f << _oss.rdbuf();

However, the buffer needs to be really big for this to make a noticeable difference. Usually, writing to disk will dominate the time needed for this anyway.

Note that I'd avoid creating identifiers with leading underscores.

Upvotes: 12

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