Constructors, references, DotNet Strings

  • Thread starter Thread starter RLF
  • Start date Start date
R

RLF

Am upgrading a C++ console app to add a DotNet Front End. Have run into a
couple of issues.

The first one is basically a c++ question. I have a class which maintains a
reference to an istringstream that is passed to it in the constructor.
Since I won't have an istream to give it from the front end, I'd like to add
another ctor that accepts a string and generates the istringstream for me so
that the reference initializer is satisfied.
Haven't found an acceptible way to do that. Could use some help.

The second question involves the string itself. I presume the ctor will most
likely need to deal with a System::String coming from the front end. I am
not familiar with the conversions available to turn that into an acceptable
type that can be handled by the istringstream constructor.

Any advice would be appreciated.
 
RLF said:
Am upgrading a C++ console app to add a DotNet Front End. Have run into a
couple of issues.

The first one is basically a c++ question. I have a class which maintains a
reference to an istringstream that is passed to it in the constructor.
Since I won't have an istream to give it from the front end, I'd like to add
another ctor that accepts a string and generates the istringstream for me so
that the reference initializer is satisfied.
Haven't found an acceptible way to do that. Could use some help.
Click to expand...

You have a lifetime issue here. The existing ctor for your class X stores a
reference to an istringstream object which must outlive the X object, and
you want to add a ctor which creates the istringstream object. One way would
be to add a smart pointer to your class, e.g.

class X
{
public:

X(istringstream& str)
: m_str(str)
{
}

X(const std::string& s)
: m_pStream(new istringstream(s)),
m_str(*m_pStream)
{
}

// Everyone uses m_str

private:

smart_ptr<istringstream> m_pStream;
istringstream& m_str;
};
The second question involves the string itself. I presume the ctor will most
likely need to deal with a System::String coming from the front end. I am
not familiar with the conversions available to turn that into an acceptable
type that can be handled by the istringstream constructor.
Click to expand...

Below is a short example which shows how to pass a System::String to the C
function puts. Once you have a pointer to an unmanaged string, you can
convert it to a std::string or whatever unmanaged type you like. See also
PtrToStringChars in the file <vcclr.h>.

#using <mscorlib.dll>
using namespace System;

#include <stdio.h>

void do_puts(String* s)
{
using namespace System::Runtime::InteropServices;

IntPtr p = Marshal::StringToHGlobalAnsi(s);
// Call unmanaged function.
puts(static_cast<const char*>(p.ToPointer()));
Marshal::FreeHGlobal(p);
}

int main()
{
String* s = S"doug";
// puts(s); // Fails - cannot convert from String* to char*
do_puts(s);
return 0;
}
 
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