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Libgit2 example more concrete #1897

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Libgit2 example more concrete #1897

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Piece of code to a concrete program
pauljoohyunkim Aug 20, 2023
e938e16
Minor paragraph edit from code modification.
pauljoohyunkim Aug 20, 2023
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52 changes: 34 additions & 18 deletions book/B-embedding-git/sections/libgit2.asc
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Original file line number Diff line number Diff line change
Expand Up @@ -10,27 +10,43 @@ Here's a whirlwind tour:

[source,c]
----
// Open a repository
git_repository *repo;
int error = git_repository_open(&repo, "/path/to/repository");

// Dereference HEAD to a commit
git_object *head_commit;
error = git_revparse_single(&head_commit, repo, "HEAD^{commit}");
git_commit *commit = (git_commit*)head_commit;

// Print some of the commit's properties
printf("%s", git_commit_message(commit));
const git_signature *author = git_commit_author(commit);
printf("%s <%s>\n", author->name, author->email);
const git_oid *tree_id = git_commit_tree_id(commit);
// If the name of this file is "head_commit_print.c", Compile this with:
// CC head_commit_print.c -o head_commit_print -lgit2
// where CC is the C compiler of your choice (eg. gcc, clang, ...)
#include <stdio.h>
#include <git2.h>

// Cleanup
git_commit_free(commit);
git_repository_free(repo);
int main()
{
// Initialize global state of git
git_libgit2_init();

// Open a repository
git_repository *repo;
int error = git_repository_open(&repo, "/path/to/repository");

// Dereference HEAD to a commit
git_object *head_commit;
error = git_revparse_single(&head_commit, repo, "HEAD^{commit}");
git_commit *commit = (git_commit*)head_commit;

// Print some of the commit's properties
printf("%s", git_commit_message(commit));
const git_signature *author = git_commit_author(commit);
printf("%s <%s>\n", author->name, author->email);
const git_oid *tree_id = git_commit_tree_id(commit);

// Cleanup
git_commit_free(commit);
git_repository_free(repo);

// Freeing resources from git_libgit2_init()
git_libgit2_shutdown();
}
----

The first couple of lines open a Git repository.
The first line in the main function initializes the global state for using libgit2 library functions.
The next couple of lines open a Git repository.
The `git_repository` type represents a handle to a repository with a cache in memory.
This is the simplest method, for when you know the exact path to a repository's working directory or `.git` folder.
There's also the `git_repository_open_ext` which includes options for searching, `git_clone` and friends for making a local clone of a remote repository, and `git_repository_init` for creating an entirely new repository.
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