Hello,
I have problems understanding why the following example does not compile in
VC7.1:
std::stringstre am test;
const std::istream& test2 = test; //OK
const std::istream& test3 = std::stringstre am(); // fails
Error is:
'std::basic_str ingstream<_Elem ,_Traits,_Alloc >::__ctor' : no non-explicit
constructor available for implicit conversion
I used to think test + test2 lines and test3 lines are equivalent but it
seems not. Any ideas?
Note: I know that test3 line will lead to undefined behaviour, but I would
like to know why it does not compile?
Thanks in advance,
SerGioGioGio 4 7733
#include<conio. h>
#include<stdio. h>
#include<iostre am.h>
#define re 1 //realis
#define im 2 //imaginalis
typedef int complex;
complex F1 (complex x[2],complex y[2]){
cout<<"Dodawani e liczb zespolonych"<<
"("<<x[re]<<"+"<<x[im]<<"i)+"<<"("< <y[re]<<"+"<<y[im]<<"i)=";
complex z[2];
z[re]=x[re]+y[re];
z[im]=x[im]+y[re];
return z;} // <========Here
void main()
{clrscr();
complex x[2],y[2];
cout<<"Podaj liczbe rzeczywista do pierwszej liczby zespolnoej x+yi x= ";
cin>>x[re];
cout<<"Podaj liczbe urojon¡ do pierwszej liczby zespolnoej x+yi y= ";
cin>>x[im];
cout<<"Podaj liczbe rzeczywista do drugiej liczby zespolnoej x+yi x= ";
cin>>y[re];
cout<<"Podaj liczbe urojon¡ do drugiej liczby zespolnoej x+yi y= ";
cin>>y[im];
complex z[2];
z=F1(x,y); // <========And here
cout<<"("<<z[re]<<"+"<<z[im]<<"i)"<<endl;
getchar();
}
morgan wrote:
The simple answer is:
you can't return an array. Just as you cannot assign
an array:
int i[5], j[5];
...
i = j; // won't work. You cannot assign arrays.
In your case a simple solution would be to *not*
use an array, but use a struct instead:
struct complex
{
int re;
int im;
};
complex F1 (complex x, complex y )
{
cout << "Dodawanie liczb zespolonych" <<
"(" << x.re << "+" << x.im << "i)+" <<
"(" << y.re << "+" << y.im << "i)=";
complex z;
z.re = x.re + y.re;
z.im = x.im + y.re;
return z;
}
void main()
int main()
{
complex x, y;
cout << "Podaj liczbe rzeczywista do pierwszej liczby zespolnoej x+yi x= ";
cin >> x.re;
cout << "Podaj liczbe urojon¡ do pierwszej liczby zespolnoej x+yi y= ";
cin >> x.im;
cout << "Podaj liczbe rzeczywista do drugiej liczby zespolnoej x+yi x= ";
cin >> y.re;
cout << "Podaj liczbe urojon¡ do drugiej liczby zespolnoej x+yi y= ";
cin >> y.im;
complex z;
z = F1( x, y );
cout << "(" << z.re << "+" << z.im << "i)" << endl;
getchar();
}
--
Karl Heinz Buchegger kb******@gascad .at
On Tue, 14 Dec 2004 08:35:55 +0100, "SerGioGio" <se*******@yaho o.fr>
wrote: Hello,
I have problems understanding why the following example does not compile in VC7.1:
std::stringstre am test; const std::istream& test2 = test; //OK const std::istream& test3 = std::stringstre am(); // fails
Error is: 'std::basic_st ringstream<_Ele m,_Traits,_Allo c>::__ctor' : no non-explicit constructor available for implicit conversion
I used to think test + test2 lines and test3 lines are equivalent but it seems not. Any ideas? Note: I know that test3 line will lead to undefined behaviour, but I would like to know why it does not compile?
You cannot bind a temporary to a non-const reference. This is to
prevent code like this compiling:
void f(int& i)
{
i = 10;
}
int main()
{
double d = 0;
f(d); //temporary int created and modified
//here d is still 0!
}
It is legal to bind a temporary to a const reference, since that can't
have the problem above.
It has been suggested that the rule would be better if it were: "You
can't bind a temporary to a non-const reference *unless binding can be
done without any implicit conversions*." Or something like that.
Tom
"SerGioGio" <se*******@yaho o.fr> wrote in message
news:41******** @news.starhub.n et.sg... Hello,
I have problems understanding why the following example does not compile
in VC7.1:
std::stringstre am test; const std::istream& test2 = test; //OK
Why 'const'. You won't be able the modify the stream
(i.e. use it to extract characters).
const std::istream& test3 = std::stringstre am(); // fails
Error is: 'std::basic_str ingstream<_Elem ,_Traits,_Alloc >::__ctor' : no non-explicit constructor available for implicit conversion
This answers your last question below. I used to think test + test2 lines and test3 lines are equivalent but it seems not. Any ideas? Note: I know that test3 line will lead to undefined behaviour, but I would like to know why it does not compile?
Thanks in advance,
Also note that streams are not copyable. (Well you *can* copy them,
but it's a convoluted process (See e.g. Josuttis), and not recommended.
What specifically are you trying to do?
-Mike This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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