是否可以使用对自定义结构的FILE *起作用的函数？

Question

Very often I see libraries that implements their own stream functionalities, instead of using FILE* . The typical interface will have a close function, similar to fclose() , and several open functions, one of which usually mimics fopen() and one of which usually accepts a few callbacks that should be used to open/close the stream, read to/write from the stream.

As a reference, good examples of what I am talking about are http://www.xmlsoft.org/xmlio.html or https://developer.gnome.org/gio/ .

The approach, in general, seems very straightforward to me, however these libraries do not usually implement a replacement for all the functions in the standard library (eg, fscanf() , fprintf() , ...).

Thus I wonder if an extension mechanism is available for standard library FILE* as well (eg: opening by providing callbacks for some low-level required functionalities). I was not able to find any reference about this capability, so I guess it is not part of any standard.

Anyway, here is my question: is this functionality available in the C standard library (any standard is fine, as long as it is portable)? If not is there any easy (ie, it does not require to re-implement the whole stdio.h functions) option that allows to implement it on top of the standard library?

Answer 1

It depends on the C library you're using. Glibc, for example, supports custom streams through fopencookie ( further documentation here ). FreeBSD (and probably other BSDs as well, including OS X) have funopen . It doesn't look like Microsoft's C library supports such a feature.