quirks.md

C quirks

This is an (incomplete) list of C quirks and current solutions for them in cxgo.

Compilation and preprocessing

#define instead of const

Due to C being C, const is not really a constant declaration. Because of this, most project define constants with the preprocessor directives like #define.

Unfortunately, cxgo lets the preprocessor replace all those constant with underlying values.

This must be fixed at some point.

Comments

Comments are usually discarded by the preprocessor.

Due to this, cxgo drops all comments for now.

This must be fixed at some point.

#include concatenating files

In C each file is processed individually with all included files concatenated together.

Thanks to information exposed by cc, cxgo can track the source file of each declaration. During translation, it tracks what file is currently active and emits only declarations from that file.

.c and .h files

cxgo considers .c and .h files as a one unit and will automatically merge declarations from both.

Different included file content with #ifdef

cxgo assumes that the user will configure all project-specific #define switches on his own.

However, there is a potential to manipulate a platform-related #define directives that are currently emulated by cxgo. We could potentially translate the same file under different OS/arch combinations and compare the resulting code. All differences can be placed into separate Go files with +build directives.

Private fields with incorrect headers

Some projects define the same struct type differently in public and private header files.

For now cxgo ignores this and lets the user control what to do in this case.

We can be smarter here and guess a private-public struct pair based on names or function signatures. We can then properly merge those structs and set private-public field names accordingly in Go.

Different stdlib headers

Each platform may have different stdlib headers. They might also be located in different places on different distros.

To solve this, cxgo emulates a virtual include file system at /_cxgo_overrides, which contain customized C stdlib headers bundled into cxgo.

It serves two purposes: provides a zero-config experience for common use cases and allows cxgo to implement C stdlib differently and adapt it to the needs of Go.

typedef void

Example from struct_FILE.h:

typedef void _IO_lock_t;

_IO_lock_t *_lock;

For now cxgo interprets it as

typedef struct{} _IO_lock_t;