Making my own printf function?

Question

I was wondering how I could do this. I'm mostly puzzled by the N arguments part:

printf("Hello, I'm %i years old and my mom is %i .",me.age(),mom.age());

I want to make a function that will take a formatted string like this and return a std string.

How is the N arguments part done?

James McNellis · Accepted Answer · 2010-12-27 03:31:16Z

10

printf is a variadic function; you can implement your own variadic functions using the facilities provided by <stdarg.h>.

In C++, you should avoid variadic functions wherever possible. They are quite limited in what types they can accept as arguments and they are not type safe. C++0x adds variadic templates to C++; once support for this feature is widespread, you'll be able to write type safe variadic functions.

In the meantime, it's best to use some other type safe method. Boost.Format, for example, overloads the % operator to perform formatting.

answered Dec 27, 2010 at 3:31

James McNellis

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10 Comments

engf-010 Over a year ago

@James McNellis: Why are variadic limited ? I think the only limitation is the stacksize. You can use any type as long as it's interpreted right.

Michael Aaron Safyan Over a year ago

@Edwin, they are limited in that you cannot pass in a user-defined structure. (E.g. passing an std::string).

James McNellis Over a year ago

@Edwin: Among other things, all arguments passed in the variable arguments pack must be POD.

James McNellis Over a year ago

@Michael: You can pass a class-type object as long as it is POD.

Clifford Over a year ago

@Micheal: ... and you can always pass a pointer to any type or array.

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