Adding add example.

examples/add.c

+#include <git2.h>
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+
+enum print_options {
+	SKIP = 1,
+	VERBOSE = 2,
+};
+
+struct print_payload {
+	enum print_options options;
+	git_repository *repo;
+};
+
+void init_array(git_strarray *array, int argc, char **argv)
+{
+	unsigned int i;
+
+	array->count = argc;
+	array->strings = malloc(sizeof(char*) * array->count);
+	assert(array->strings!=NULL);
+
+	for(i=0; i<array->count; i++) {
+		array->strings[i]=argv[i];
+	}
+
+	return;
+}
+
+int print_matched_cb(const char *path, const char *matched_pathspec, void *payload)
+{
+	(void)matched_pathspec;
+
+	struct print_payload p = *(struct print_payload*)(payload);
+	int ret;
+	git_status_t status;
+
+	if (git_status_file(&status, p.repo, path)) {
+		return -1; //abort
+	}
+
+	if (status & GIT_STATUS_WT_MODIFIED ||
+	         status & GIT_STATUS_WT_NEW) {
+		if (p.options & VERBOSE || p.options & SKIP) {
+			printf("add '%s'\n", path);
+		}
+		ret = 0;
+	} else {
+		ret = 1;
+	}
+
+	if(p.options & SKIP) {
+		ret = 1;
+	}
+
+	return ret;
+}
+
+int main (int argc, char** argv)
+{
+	git_index_matched_path_cb matched_cb = NULL;
+	git_repository *repo = NULL;
+	git_index *index;
+	git_strarray array = {0};
+	int i, options = 0;
+	struct print_payload payload = {0};
+
+	if (argc < 2) {
+		fprintf(stderr, "usage: add file-spec [file-spec] [...]\n");
+		return 1;
+	}
+
+	for (i = 1; i < argc; ++i) {
+		if (argv[i][0] != '-') {
+			break;
+		}
+		else if(!strcmp(argv[i], "--verbose") || !strcmp(argv[i], "-v")) {
+			options |= VERBOSE;
+		}
+		else if(!strcmp(argv[i], "--dry-run") || !strcmp(argv[i], "-n")) {
+			options |= SKIP;
+		}
+		else if(!strcmp(argv[i], "--")) {
+			break;
+		}
+		else {
+			fprintf(stderr, "Unsupported option %s.\n", argv[i]);
+			return 1;
+		}
+	}
+	
+	init_array(&array, argc-i, argv+i);
+
+	printf("args:\n");
+	for(i=0; i<array.count; i++) {
+		printf(" - %s\n", array.strings[i]);
+	}
+
+	if (git_repository_open(&repo, ".") < 0) {
+		fprintf(stderr, "No git repository\n");
+		return 1;
+	}
+
+	if (git_repository_index(&index, repo) < 0) {
+		fprintf(stderr, "Could not open repository index\n");
+		return 1;
+	}
+
+	matched_cb = &print_matched_cb;
+
+	payload.options = options;
+	payload.repo = repo;
+	git_index_add_all(index, &array, 0, matched_cb, &payload);
+
+	git_index_write(index);
+	git_index_free(index);
+	git_repository_free(repo);
+
+	return 0;
+}