main.c

#include <stdio.h>
#include "git2.h"

// Build: gcc -o main -lgit2 main.c

void print_error(int error_code, const char *action)
{
  const git_error *error = giterr_last();
  if (!error_code)
    return;

  printf("Error %d %s - %s\n", error_code, action,
      (error && error->message) ? error->message : "???");

  exit(1);
}

int main() {
  const char* name = "foo.bar";
  const char* value = "baz";

  git_libgit2_init();

  int error = 0;

  git_config *cfg = NULL;

  error = git_config_open_default(&cfg);
  print_error(error, "open_default");

  git_config *global_cfg = NULL;
  error = git_config_open_global(&global_cfg, cfg);
  print_error(error, "open_global");

  error = git_config_set_string(global_cfg, name, value);
  print_error(error, "set_string");
  // This fails with
  // Error -1 set_string - failed to stat '/Users/user/.gitconfig/Users/user/workspace/dotfiles/.gitconfig': Not a directory
  // when /Users/user/.gitconfig -> /Users/user/workspace/dotfiles/.gitconfig

  git_config *snap_cfg = NULL;
  error = git_config_snapshot(&snap_cfg, global_cfg);
  print_error(error, "config_snapshot");

  const char* result = NULL;
  error = git_config_get_string(&value, snap_cfg, name);
  print_error(error, "get_string");

  printf("foo.bar is %s\n", result);

  git_libgit2_shutdown();
  return 0;
}