[c++] How to write a large buffer into a binary file in C++, fast?

Could you use FILE* instead, and the measure the performance you've gained? A couple of options is to use fwrite/write instead of fstream:

#include <stdio.h>

int main ()
{
  FILE * pFile;
  char buffer[] = { 'x' , 'y' , 'z' };
  pFile = fopen ( "myfile.bin" , "w+b" );
  fwrite (buffer , 1 , sizeof(buffer) , pFile );
  fclose (pFile);
  return 0;
}

If you decide to use write, try something similar:

#include <unistd.h>
#include <fcntl.h>

int main(void)
{
    int filedesc = open("testfile.txt", O_WRONLY | O_APPEND);

    if (filedesc < 0) {
        return -1;
    }

    if (write(filedesc, "This will be output to testfile.txt\n", 36) != 36) {
        write(2, "There was an error writing to testfile.txt\n", 43);
        return -1;
    }

    return 0;
}

I would also advice you to look into memory map. That may be your answer. Once I had to process a 20GB file in other to store it in the database, and the file as not even opening. So the solution as to utilize moemory map. I did that in Python though.

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