C++ question - functions taking dynamic number of arguments...

[Superwormy]

Some C++ functions I've noticed take a random length list of arguements, for instance the .NET Console::Write method, you can do:

Console::Write ("just one");
Console::Write ("one", "two", aString, "three");
Console::Write ("yet", "another", "example", "using", "bunch", "of", arguments");

etc. etc.

cout does the same, you can say:
cout << " string one " << "string two";

I want to write a function that can take any random number of arguments like this... how?

function myFunction ( [ what do I put for arguments, and how to I access them? ] )
{
// stuff goes here
}

 

[PrincessGuard]

http://gethelp.devx.com/techtips/cpp_pro/10min/2001/feb/10min0201.asp

 

[Argo]

What you need is an "ellipse" operator. I'm not too familiar with the syntax but Im sure you can find plenty of material on this.


And FYI, cout doesn't work that way. The reason it works is because << returns cout itself. So it's equivalent to doing something like this:


cout.write("one").write("two").write("three");

Where each write returns the cout stream itself.

 

[Barnaby W. Füi]

Originally posted by: Argo
What you need is an "ellipse" operator. I'm not too familiar with the syntax but Im sure you can find plenty of material on this.


And FYI, cout doesn't work that way. The reason it works is because << returns cout itself. So it's equivalent to doing something like this:


cout.write("one").write("two").write("three");

Where each write returns the cout stream itself.

Ah cool, good to know exactly how that works.

Also, in C++, you can have default arguments, which are somewhat similar to variable arguments, but generally have different uses:

int fooBar(int s, int d=5, char * f="hello") {
.....
}

I might be a tiny bit off, I'm not quite a C++ person.

 

[BFG10K]

To use variable arguments in C/C++ you put an an ellipses (...) in the function prototype/header and then you use commands such as va_list, va_start and va_args to extract them.

It's too complicated to explain in a thread but if you look into any C/C++ guide for those keywords you'll find what you're looking for.

I've used variable arguments quite a few times and they're incredibly useful.

 

[Argo]

Originally posted by: BingBongWongFooey

Originally posted by: Argo
What you need is an "ellipse" operator. I'm not too familiar with the syntax but Im sure you can find plenty of material on this.


And FYI, cout doesn't work that way. The reason it works is because << returns cout itself. So it's equivalent to doing something like this:


cout.write("one").write("two").write("three");

Where each write returns the cout stream itself.

Ah cool, good to know exactly how that works.

Also, in C++, you can have default arguments, which are somewhat similar to variable arguments, but generally have different uses:

int fooBar(int s, int d=5, char * f="hello") {
.....
}

I might be a tiny bit off, I'm not quite a C++ person.

You're close - you do use default arguments that way, however you do that in the function declaration not defintion. For example:

void myFunc(int a, int b = 10, int c = 11);

void myFunc(int a, int b, int c) {
// ....
}

Also, I'm not sure you can use default arguments with non primitive types, i.e. strings, arrays.

 

[Barnaby W. Füi]

Originally posted by: Argo

You're close - you do use default arguments that way, however you do that in the function declaration not defintion. For example:

void myFunc(int a, int b = 10, int c = 11);

void myFunc(int a, int b, int c) {
// ....
}

aah.

Also, I'm not sure you can use default arguments with non primitive types, i.e. strings, arrays.

For some reason, that occured to me as well, so I kept my example simple.

edit: I don't even think char * foo = "hello" is correct, I think it'd have to be char foo[] = "hello", assuming you can even use arrays.

 

[Superwormy]

excellent, thanks!

 

[singh]

I don't recommend that you use the ellipses to pass variable number of arguments. It's unsafe and doesn't really fit with the C++ philosophy.

 

[Barnaby W. Füi]

Originally posted by: singh
I don't recommend that you use the ellipses to pass variable number of arguments. It's unsafe and doesn't really fit with the C++ philosophy.

What is unsafe about it?

 

[PrincessGuard]

Originally posted by: BingBongWongFooey

Originally posted by: singh
I don't recommend that you use the ellipses to pass variable number of arguments. It's unsafe and doesn't really fit with the C++ philosophy.

What is unsafe about it?

No type checking.

 

[Ameesh]

Originally posted by: BFG10K
To use variable arguments in C/C++ you put an an ellipses (...) in the function prototype/header and then you use commands such as va_list, va_start and va_args to extract them.

It's too complicated to explain in a thread but if you look into any C/C++ guide for those keywords you'll find what you're looking for.

I've used variable arguments quite a few times and they're incredibly useful.

exactly correct

 

[Ameesh]

Originally posted by: PrincessGuard

Originally posted by: BingBongWongFooey

Originally posted by: singh
I don't recommend that you use the ellipses to pass variable number of arguments. It's unsafe and doesn't really fit with the C++ philosophy.

What is unsafe about it?

No type checking.

ROFL! a lot of C/C++ coders considers that an advantage, its not a type safe language to begin with, people pass around void * all the time to avoid type checking. it is the power and pitfall of C

 

[Ameesh]

Originally posted by: PrincessGuard

Originally posted by: BingBongWongFooey

Originally posted by: singh
I don't recommend that you use the ellipses to pass variable number of arguments. It's unsafe and doesn't really fit with the C++ philosophy.

What is unsafe about it?

No type checking.

ROFL! a lot of C/C++ coders considers that an advantage, its not a type safe language to begin with, people pass around void * all the time to avoid type checking. it is the power and pitfall of C

 

[singh]

Originally posted by: Ameesh

Originally posted by: PrincessGuard

Originally posted by: BingBongWongFooey

Originally posted by: singh
I don't recommend that you use the ellipses to pass variable number of arguments. It's unsafe and doesn't really fit with the C++ philosophy.

What is unsafe about it?

No type checking.

ROFL! a lot of C/C++ coders considers that an advantage, its not a type safe language to begin with, people pass around void * all the time to avoid type checking. it is the power and pitfall of C

While some people do exactly what you say, it certainly doesn't make it right. The same guys also complain it's so hard to debug C++ programs!

 

[Ameesh]

Originally posted by: singh

Originally posted by: Ameesh

Originally posted by: PrincessGuard

Originally posted by: BingBongWongFooey

Originally posted by: singh
I don't recommend that you use the ellipses to pass variable number of arguments. It's unsafe and doesn't really fit with the C++ philosophy.

What is unsafe about it?

No type checking.

ROFL! a lot of C/C++ coders considers that an advantage, its not a type safe language to begin with, people pass around void * all the time to avoid type checking. it is the power and pitfall of C

While some people do exactly what you say, it certainly doesn't make it right. The same guys also complain it's so hard to debug C++ programs!

it doesnt make it wrong either.

YOURE NOT THE BOSS OF ME!





lol