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Libgit2 Conventions

We like to keep the source consistent and readable. Herein are some guidelines that should help with that.

Naming Things

All types and functions start with git_, and all #define macros start with GIT_.

Functions with a single output parameter should name that parameter out. Multiple outputs should be named foo_out, bar_out, etc.

Parameters of type git_oid should be named id, or foo_id. Calls that return an OID should be named git_foo_id.

Where there is a callback passed in, the void * that is passed into it should be named "payload".


Wherever possible, use typedef. If a structure is just a collection of function pointers, the pointer types don't need to be separately typedef'd, but loose function pointer types should be.


All exported functions must be declared as:

GIT_EXTERN(result_type) git_modulename_functionname(arg_list);


Functions whose modulename is followed by two underscores, for example git_odb__read_packed, are semi-private functions. They are primarily intended for use within the library itself, and may disappear or change their signature in a future release.


Out parameters come first.

Whenever possible, pass argument pointers as const. Some structures (such as git_repository and git_index) have internal structure that prevents this.

Callbacks should always take a void * payload as their last parameter. Callback pointers are grouped with their payloads, and come last when passed as arguments:

int foo(git_repository *repo, git_foo_cb callback, void *payload);

Memory Ownership

Some APIs allocate memory which the caller is responsible for freeing; others return a pointer into a buffer that's owned by some other object. Make this explicit in the documentation.

Return codes

Return an int when a public API can fail in multiple ways. These may be transformed into exception types in some bindings, so returning a semantically appropriate error code is important. Check errors.h for the return codes already defined.

Use giterr_set to provide extended error information to callers.

If an error is not to be propagated, use giterr_clear to prevent callers from getting the wrong error message later on.

Opaque Structs

Most types should be opaque, e.g.:

typedef struct git_odb git_odb;

...with allocation functions returning an "instance" created within the library, and not within the application. This allows the type to grow (or shrink) in size without rebuilding client code.

To preserve ABI compatibility, include an int version field in all opaque structures, and initialize to the latest version in the construction call. Increment the "latest" version whenever the structure changes, and try to only append to the end of the structure.

Option Structures

If a function's parameter count is too high, it may be desirable to package up the options in a structure. Make them transparent, include a version field, and provide an initializer constant or constructor. Using these structures should be this easy:

git_foo_options opts = GIT_FOO_OPTIONS_INIT;
opts.baz = BAZ_OPTION_ONE;


Typedef all enumerated types. If each option stands alone, use the enum type for passing them as parameters; if they are flags, pass them as unsigned int.

Code Layout

Try to keep lines less than 80 characters long. Use common sense to wrap most code lines; public function declarations should use this convention:

GIT_EXTERN(int) git_foo_id(
   git_oid **out,
   int a,
   int b);

Indentation is done with tabs; set your editor's tab width to 3 for best effect.


All comments should conform to Doxygen "javadoc" style conventions for formatting the public API documentation. Try to document every parameter, and keep the comments up to date if you change the parameter list.

Public Header Template

Use this template when creating a new public header.

#ifndef INCLUDE_git_${filename}_h__
#define INCLUDE_git_${filename}_h__

#include "git/common.h"

 * @file git/${filename}.h
 * @brief Git some description
 * @defgroup git_${filename} some description routines
 * @ingroup Git
 * @{

/* ... definitions ... */

/** @} */
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