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basic_ostream question

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  basic_ostream question Ruben Safir <ruben@mrbrklyn.com> - 2011-06-01 01:45 +0000
    Re: basic_ostream question red floyd <no.spam.here@its.invalid> - 2011-05-31 21:50 -0700
      Re: basic_ostream question ruben safir <ruben@mrbrklyn.com> - 2011-06-02 22:44 -0400
        Re: basic_ostream question Michael Doubez <michael.doubez@free.fr> - 2011-06-03 02:56 -0700

#5934 — basic_ostream question

can simeone explain why the last 3 lines don't behave like expected

#include <iomanip>


int main(int argv, char ** argc){

   char x = 'm';
   float a = 3.14, b = 9.3453, e = 3, f = 1/3;
   f = (1.0 / 3);
   short c = 6;
   std::cerr.write( "x = ", 4);
   std::cerr.put(x);
   std::cerr.put( '\n');
   std::cerr << "x = " << x << std::endl;
   std::cout << "a + b + c = " << std::scientific << a + b + c << " hello World" << std::endl;
   std::cout << "a + b + c = " << std::fixed << a + b + c << std::endl;
   std::cout << "e * f  = " << e << " * " << f << "=" << e * f << std::endl;
   ((std::cout.write("x= ", 3)).operator<<(x)).operator<<(std::endl);
   ((std::cout.operator<<("x= ")).operator<<(x)).operator<<(std::endl);
   std::cout << "x = " << x << std::endl;
}

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#5937

On 5/31/2011 6:45 PM, Ruben Safir wrote:
> can simeone explain why the last 3 lines don't behave like expected
>
> #include<iomanip>
>
>
> int main(int argv, char ** argc){
>
>     char x = 'm';
>     float a = 3.14, b = 9.3453, e = 3, f = 1/3;
>     f = (1.0 / 3);
>     short c = 6;
>     std::cerr.write( "x = ", 4);
>     std::cerr.put(x);
>     std::cerr.put( '\n');
>     std::cerr<<  "x = "<<  x<<  std::endl;
>     std::cout<<  "a + b + c = "<<  std::scientific<<  a + b + c<<  " hello World"<<  std::endl;
>     std::cout<<  "a + b + c = "<<  std::fixed<<  a + b + c<<  std::endl;
>     std::cout<<  "e * f  = "<<  e<<  " * "<<  f<<  "="<<  e * f<<  std::endl;
>     ((std::cout.write("x= ", 3)).operator<<(x)).operator<<(std::endl);
>     ((std::cout.operator<<("x= ")).operator<<(x)).operator<<(std::endl);
>     std::cout<<  "x = "<<  x<<  std::endl;
> }
>

Ignoring the missing #include <iostream>, exactly how were you
expecting it to behave, and what did you see instead?

Please see FAQ 5.8

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#6119

On 06/01/2011 12:50 AM, red floyd wrote:
> ((std::cout.operator<<("x= ")).operator<<(x)).operator<<(std::endl);


well for one thing, this one I didn't expect to get hex code.

Ruben

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#6128

On 3 juin, 04:44, ruben safir <ru...@mrbrklyn.com> wrote:
> On 06/01/2011 12:50 AM, red floyd wrote:
>
> > ((std::cout.operator<<("x= ")).operator<<(x)).operator<<(std::endl);
>
> well for one thing, this one I didn't expect to get hex code.

Because, the only ioperator available is:
basic_ostream<charT,traits>& operator<<(const void* p);

Which writes the pointer value (like %#p in printf).

The string version is the free function:

template<class charT, class traits>
basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&
out,
const char* s);
// ... other templates cf. 27.6.2.5.4 of the standard

Which computes the length and inserts the string into the stream.
AFAIK there are no corresponding function in the std::ostream
interface (for formated output).

--
Michael

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