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complex number

Posted on 1999-01-24
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this question goes out t othose who have experience in BCB3.
recently, i tried to used the complex class in a SDI application. i declared a variable like this:

#include <complex.h>
complex EM;

the complier gave an error message :"illegal use of template."
Whats wrong ?
can someone pls explained.
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Question by:deuter
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Zoppo earned 400 total points
ID: 1185041
I do not know BCB3, but I know that complex is a template class needing a type as parameter like this:

#include <complex.h>
complex <float> EM;   // create a complex using floats
complex <double> EM_1;   // create a complex using doubles

Explanation:
copmlex is defined as template like this:
------------------------------------------------------------
template<class T> class complex
{
    public:    typedef T value_type;
// and so on ...
------------------------------------------------------------
This tells the compiler to create a own class complex for any type with which it's used (thats the sense of templates).

so you must declare the type !!


hope that help,

ZOPPO
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Author Comment

by:deuter
ID: 1185042
zoppo, thanks for the explanation, can you show me where i can get more info for the template?
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LVL 31

Expert Comment

by:Zoppo
ID: 1185043
I think you just will have to buy a good C++ book to learn more about templates. I can give you a short description:

the expression 'template <class T(,...)>' before a class or function definition tells the compiler to create one class/function for each different type used.

For example:

template <class T> class X // example of a simple template class X
{
public:
typedef T calue_type;

value_type m_data;
void SetData( value_type data ) { m_data = data };
value_type GetData( void ){ return m_data };
.
}

template <class T> T mymin( T w1, T w2 ) // template function mymin
{
if ( w1 < w2 )
   return w1;
else
   return w2;
}

X<char> x_char;               // creates a class X with value_type char
X<double> x_double;        // creates a class X with value_type double
X<CString> x_string;        // creates a class X with value_type CString

int i = mymin( 5, 3 );        // create a call to a funtion 'int mymin( int 5, int 3 );' - returns 3
double d = mymin( 5.3, 7.4 );      // create a call to a funtion 'double mymin( double, double );' - returns 5.2
CString test = mymin( "world", "Hello, " );  // create a call to a funtion CString mymin( CString, CString );' - returns "Hello, world"

that not a good explanaition, but it's all I ever needed to know. But allthough I think it's good to have a good C++ book to learn this more detailed.

hope that helps,

ZOPPO
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