C++ Any faster method to write a large binary file?

Question

Goal

My goal is to quickly create a file from a large binary string (a string that contains only 1 and 0).

Straight to the point

I need a function that can achieve my goal. If I am not clear enough, please read on.

Example

Test.exe is running...
.
Inputted binary string:
        1111111110101010
Writing to: c:\users\admin\desktop\Test.txt
        Done!
File(Test.txt) In Byte(s):
        0xFF, 0xAA
.
Test.exe executed successfully!

Explanation

• First, Test.exe requested the user to input a binary string.
• Then, it converted the inputted binary string to hexadecimal.
• Finally, it wrote the converted value to a file called Test.txt.

I've tried

As an fail attempt to achieve my goal, I've created this simple (and possibly horrible) function (hey, at least I tried):

void BinaryStrToFile( __in const char* Destination,
                      __in std::string &BinaryStr )
{
    std::ofstream OutputFile( Destination, std::ofstream::binary );

    for( ::UINT Index1 = 0, Dec = 0;
         // 8-Bit binary.
         Index1 != BinaryStr.length( )/8;

         // Get the next set of binary value.
         // Write the decimal value as unsigned char to file.
         // Reset decimal value to 0.
         ++ Index1, OutputFile << ( ::BYTE )Dec, Dec = 0 )
    {
        // Convert the 8-bit binary to hexadecimal using the
        // positional notation method - this is how its done:
        // http://www.wikihow.com/Convert-from-Binary-to-Decimal
        for( ::UINT Index2 = 7, Inc = 1; Index2 + 1 != 0; -- Index2, Inc += Inc )
            if( BinaryStr.substr( Index1 * 8, 8 )[ Index2 ] == '1' ) Dec += Inc;
    }
    OutputFile.close( );
};

Example of usage

#include "Global.h"

void BinaryStrToFile( __in const char* Destination,
                      __in std::string &BinaryStr );

int main( void )
{
    std::string Bin = "";

    // Create a binary string that is a size of 9.53674 mb
    // Note: The creation of this string will take awhile.
    // However, I only start to calculate the speed of writing
    // and converting after it is done generating the string.
    // This string is just created for an example.
    std::cout << "Generating...\n";
    while( Bin.length( ) != 80000000 )
        Bin += "10101010";

    std::cout << "Writing...\n";
    BinaryStrToFile( "c:\\users\\admin\\desktop\\Test.txt", Bin );

    std::cout << "Done!\n";
#ifdef IS_DEBUGGING
    std::cout << "Paused...\n";
    ::getchar( );
#endif

    return( 0 );
};

Problem

Again, that was my fail attempt to achieve my goal. The problem is the speed. It is too slow. It took more than 7 minutes. Are there any method to quickly create a file from a large binary string?

Thanks in advance,

CLearner

Answer 1

I'd suggest removing the substr call in the inner loop. You are allocating a new string and then destroying it for each character that you process. Replace this code:

for(::UINT Index2 = 7, Inc = 1; Index2 + 1 != 0; -- Index2, Inc += Inc )
    if( BinaryStr.substr( Index1 * 8, 8 )[ Index2 ] == '1' )
        Dec += Inc;

by something like:

for(::UINT Index2 = 7, Inc = 1; Index2 + 1 != 0; -- Index2, Inc += Inc )
    if( BinaryStr[Index1 * 8 + Index2 ] == '1' )
        Dec += Inc;

Answer 2

The majority of your time is spent here:

   for( ::UINT Index2 = 7, Inc = 1; Index2 + 1 != 0; -- Index2, Inc += Inc )
        if( BinaryStr.substr( Index1 * 8, 8 )[ Index2 ] == '1' ) Dec += Inc;

When I comment that out the file is written in seconds. I think you need to finetune your conversion.