istringstream and optimization

[mathieu]

Hello there,

Could anyone comment on the following code(*). I would like to
optimize the following line:

is.str( std::string(s,4) );

Seems to me that allocation+initialization of the std::string is a
bit complex for such simple task. Looks to me that I should be able to
manipulate the rdbuf internals.

Comments welcome, thanks.
Mathieu

(*)
#include <iostream>
#include <sstream>

int main()
{
// 9728
const char s[] = "\0&\0\0";
uint32_t n = 0;
memcpy(&n, s, 4);
std::cout << n << std::endl;

uint32_t nn = 0;
std::istringstream is;
is.str( std::string(s,4) ); // <----- this line
is.read( reinterpret_cast<char*>(&nn), 4);
std::cout << is.str() << "->" << nn << std::endl;

std:stringstream os;
os.write( reinterpret_cast<char*>(&n), 4);
std::cout << n << "->" << os.str() << std::endl;

return 0;
}

 

[red floyd]

Hello there,

Could anyone comment on the following code(*). I would like to
optimize the following line:

is.str( std::string(s,4) );

Seems to me that allocation+initialization of the std::string is a
bit complex for such simple task. Looks to me that I should be able to
manipulate the rdbuf internals.

Have you benchmarked to see if this actually is a problem? What is the
obsession that people seem to have with premature optimization, without
regard to Hoare's/Knuth's Law ("Premature optimization is the root of
all evil")?

Manipulating the rdbuf internals will most likely lead to less
understandable and therefore less maintainable code.

I'd code for what my last job used to call the "X-abilities"
(reliability, scalability, maintainability), and worry about
micromanaging performance later, after testing and benchmarks indicate a
problem.

But that's just my opinion.

 

[mathieu]

And the solution is...that you are indeed right !
I was going back and forth in my istringstream/ostringstream. Redoing
my templates I was able to skip this step

Mathieu