Thread: string and function parameter

Hello,
I've been trying to use std:: string with the function's ... functionality. I know how to do it with char*. Anyone can help?

Code:

void Error (string format, ...)
{
   va_list ap;
   va_start, va_end, etc... im confused a bit here.
}

What?
I was asking about the ... parameter.Read it again.

I think we need to see the entire function, or at least tell us what the function does. I don't understand what you want to do, but I don't think variadic functions (functions with a variable arguments list) are a good solution usually ...

Variadic functions, that one. Didn't know the term. Now, what didn't I explain well? I want to create a string from the variable argument list in the function parameters..

Try:

Code:

void Error (string format, ...) {
   string* pErr = &format + sizeof(string);
   string& errString = *pErr;
}

...

std::string err = "Some error";
Error("some format", err);

I'm not sure if copy constructors etc. get called in variadic functions though, so if that doesn't work then:

Code:

void Error (string format, ...) {
   string** ppErr = &format + sizeof(string);
   string* pErrString = *ppErr;
   string& errString = *pErrString;
}

...

std::string err = "Some error";
Error("some format", &err);

Code:

void Error(const string& format, ...)
{
   unsigned char* byteIndex = &format + sizeof(format);
   for(std::string::const_iterator it = format.begin(); it != format.end(); ++it)
   {
	  switch(*it)
	  {
	  case 's': //Argument is a string*
		 string& err = **(string**)byteIndex;
		 byteIndex += sizeof(string*);
		 cout << err << std::endl;
		 break;
	  case 'i': //Argument is an int
		 int& err = *(int*)byteIndex;
		 byteIndex += sizeof(int);
		 cout << err << std::endl;
		 break;
	
	  etc..
	  }
   }
}
 
int main()
{
   ...
   string err = "Error";
   int errCode = 5;
   Error("is", errCode, &err);
}

I'm guessing you're trying to do something along those lines? I haven't tested it and I don't recall exactly how everything works, but that should be close enough for it to work with just a little tinkering.

If I remember correctly, the standard doesn't permit passing non-POD objects as variable parameters.

Cool I will try all and post the reuslts! thanks