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C++ and var_list

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Quote:
Original post by NamelessTwo
Is there a C++ alternative to these?
va_arg
va_end
va_start


Try this.

#include

using namespace std;

Quote:
How to implement a function in C++ with unknown number or parameters?


You can't pass objects through the ellipsis. You can pass pointers to objects.

By using the ellipsis, you forfeit the string type checking and compile-time safety available through C++.

Notice how in the C++ standard library the use of varargs functions is replaced by chaining operators (eg. cout vs. printf).

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See boost::format for an example where C++ operator chaining improved on the vast shortcomings of the printf-style ellipsis construct.

Can't resist to quote Zahlman's signature:
"Basically whenever you invoke the dread ellipses construct you leave the happy world of type safety." -- SiCrane

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Here's a little example of how you can overload the << operator to perform chaining. Note that the result of the operation is a reference to the object itself.


struct _func {
_func& operator <<(const int i) { /* do stuff with int */; return *this; }
_func& operator <<(const double f) { /* do stuff with double */ return *this; }
_func& operator <<(const std::string& s) { /* do stuff with string */; return *this; }
} func;


func << 42 << "Hello" << "world" << 3.14;


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Quote:
Original post by Konfusius
See boost::format for an example where C++ operator chaining improved on the vast shortcomings of the printf-style ellipsis construct.


However, even boost::format's developers note that it is considerably slower than printf. I guess I mention this just to bring notice to the fact that the 'best' way of doing something is not always the most suitable for a given situation, although I agree that the elipses should be avoided whenever possible.

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This topic is 4395 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

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