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Alex Vinokur · Guest

Technical Report on C++ Performance
ISO/IEC PDTR 18015; Date: 2003-08-11; WG21 N1487=03-0070
* http://std.dkuug.dk/JTC1/SC22/WG21/docs/PDTR18015.pdf
* http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1487.pdf

Appendix D: Timing Code

D.5 Measuring the Cost of Synchronized I/O

<QUOTE>
Test program to
(1) compare the performance of classic iostreams,
standard iostreams, and C-style stdio for output, and
(2) test any overhead of sync_with_stdio(true). Standard
iostreams by default are synchronized with stdio streams;
the opposite was true of classic iostreams.
optional command line argument:
- how many numbers to output (default 1,000,000)
- name of output file (default cout)
When compiling, define CLASSIC or STDIO to enable
those options; otherwise the default is to use
standard iostreams.

#if defined (STDIO)
#include <stdio.h>
#elif defined (CLASSIC)
#include <iostream.h>
#include <fstream.h>
#else
#include <iostream> // use standard iostreams
#include <fstream>
using namespace std;
#endif

</QUOTE>

Here are two programs which use classic and standard iostreams.

One can see that GNU g++ compiler generates the same code for both programs.

Is there any situation that different assembly code is generated while using classic and standard iostreams ?

====== foo1.cpp ======
// classic iostreams

#include <iostream.h>

int main ()
{
cout.sync_with_stdio (false);
cout << 123 << endl;

cout.sync_with_stdio (true);
cout << 456 << endl;

return 0;
}

======================

====== foo2.cpp ======
// standard iostreams

#include using namespace std;

int main ()
{
cout.sync_with_stdio (false);
cout << 123 << endl;

cout.sync_with_stdio (true);
cout << 456 << endl;

return 0;
}

======================

====== Compilation & Comparison ======

$ g++ -Wno-deprecated -save-temps foo1.cpp

$ g++ -save-temps foo2.cpp

$ diff foo1.s foo2.s
1c1
< .file "foo1.cpp"
---

P.J. Plauger · Guest

"Alex Vinokur" <alexvn (AT) bigfoot (DOT) com> wrote

Alex Vinokur · Guest

"P.J. Plauger" <pjp (AT) dinkumware (DOT) com> wrote

kanze@gabi-soft.fr · Guest

"Alex Vinokur" <alexvn (AT) bigfoot (DOT) com> wrote