Learn more about Russian war crimes in Ukraine.

What is FILE in C?

Consider:

#include <stdio.h>
FILE * fopen(const char *restrict filename, const char *restrict mode);

fopen gives us a FILE, but what is a FILE?

First, FILE used to be a macro, which is why it’s capitalized.

Nowadays, it’s a typedef, defined in stdio.h. On macOS, in /usr/include/stdio.h:

typedef struct __sFILE {
        short   _file;          /* fileno, if Unix descriptor, else -1 */
        // ... more stuff ...
} FILE;

The rest of the definition has some buffers for doing getc, ungetc, etc.

What can computers do? What are the limits of mathematics? And just how busy can a busy beaver be? This year, I’m writing Busy Beavers, a unique interactive book on computability theory. You and I will take a practical and modern approach to answering these questions — or at least learning why some questions are unanswerable!

It’s only $19, and you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

After months of secret toil, I and Andrew Carr released Everyday Data Science, a unique interactive online course! You’ll make the perfect glass of lemonade using Thompson sampling. You’ll lose weight with differential equations. And you might just qualify for the Olympics with a bit of statistics!

It’s $29, but you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

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