bscanf is a standalone sscanf implementation with bounds checking, written in ANSI C (C89). It aims to be a faithful recreation of sscanf, but includes mandatory bounds checking on character sequence-esque types (read on for more information).

It was designed primarily because Intel SGX does not support the <stdio.h> header file 1, as SGX limits I/O inside of an enclave. However, sscanf functionality is helpful in parsing data and has no dependencies on I/O. Hence, bscanf was born.

To use bscanf, simply add copy the source file bscanf.c and include the header file bscanf.h in your project. It has been tested on Linux (GCC) and macOS (Clang) under --std=c89, but it (should) work anywhere you have an ANSI C environment. Open an issue if you are having trouble.

For the most part, bscanf works like the C89 version of sscanf does. It works based on "conversion specifications": the printf format strings you know and love. It accepts the length modifiers h (for type short) and l (for type long). You can also suppress assignment like in sscanf with *. The return value of a call to bscanf is the number of variables it sets. Refer to online documentation 2 for more information on these specifiers.

However, there is one major caveat to bscanf: all character sequence types must have a maximum field width. These look like "%*3c" and "%8s". bscanf does bounds checking on c and s types to make sure it is not pushing more data than the maximum allowed width into a buffer. Note that the specifier for s (string) types must hold room for the width + 1 (for the \0 terminator), just like in sscanf; a specifier %8s would need to be 9 bytes long. To load a single character, use %1c.

If there is no width set for these specifiers, bscanf terminates the parsing of the buffer early. It also stops parsing partway when it encounters "undefined behavior" (such as %*n as a specifier). Make sure you check the result of a call to bscanf before using variables!

Please refer to the tests in test_bscanf.c for example usage. You can make the tests with the included Makefile.

The following specifiers are not supported at this time. I hope to implement these in a future version of bscanf.

• %[: match characters from a set.
• %ls, %lc: match characters/strings of wchar_t.
• %p: match a pointer.
• %a,%A: match a float in C99's hexadecimal exponent notation 3.

Additionally, bscanf does not implement the length modifiers hh, ll, j, z, t or L.