First commit, fixed appending, create, destroy and get, all working fine

.gitignore

@@ -0,0 +1,54 @@
+# Directories
+build/
+build-*/
+cmake-build-*/
+.cache/
+out/
+out/Debug/
+out/Release/
+
+# Cmake files
+CMakeCache.txt
+CMakeFiles/
+cmake_install.cmake
+CTestTestfile.cmake
+Testing/
+compile_commands.json
+../compile_commands.json
+build/compile_commands.json
+
+# Make / Ninja
+Makefile
+*.ninja
+*.ninja_deps
+*.ninja_log
+rules.ninja
+
+# Object files
+*.o
+*.obj
+*.lo
+*.la
+
+# Binaries
+*.out
+*.exe
+*.dll
+*.so
+*.so.*
+*.dylib
+*.a
+
+# Debug / Sanitizer
+*.dSYM/
+*.gcno
+*.gcda
+*.gcov
+
+# Editors
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.16)
+project(linkedlist VERSION 1.0 LANGUAGES C)
+
+set(CMAKE_C_STANDARD 11)
+set(CMAKE_C_STANDARD_REQUIRED ON)
+
+# Export compile_commands.json (para clangd)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+
+# Warnings globales
+add_compile_options(
+    -Wall
+    -Wextra
+    -Wpedantic
+)
+
+# ------------------------
+# Library
+# ------------------------
+
+add_library(linkedlist
+    src/linkedlist.c
+)
+
+target_include_directories(linkedlist
+    PUBLIC
+        ${PROJECT_SOURCE_DIR}/include
+)
+
+# ------------------------
+# Testing
+# ------------------------
+
+enable_testing()
+add_subdirectory(tests)
+

include/linkedlist.h

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+#ifndef LINKEDLIST_H
+#define LINKEDLIST_H
+
+#include <stdlib.h>
+
+typedef struct LinkedList LinkedList;
+
+typedef enum {
+    LLIST_OK = 0,
+    LLIST_ALLOC,
+    LLIST_NULL,
+    LLIST_NULL_ARG,
+    LLIST_OUT_OF_BOUNDS,
+    LLIST_INVALID_SIZE,
+} LinkedListErr;
+
+LinkedListErr linkedlist_create(LinkedList **out, size_t elem_size);
+LinkedListErr linkedlist_destroy(LinkedList *ll);
+
+LinkedListErr linkedlist_append(LinkedList *ll, void *data);
+LinkedListErr linkedlist_delete(LinkedList *ll, size_t index);
+LinkedListErr linkedlist_pop(LinkedList *ll, size_t index, void *out);
+LinkedListErr linkedlist_insert(LinkedList *ll, size_t index, void *out);
+LinkedListErr linkedlist_get(const LinkedList *ll, size_t index, void *out);
+
+#endif /* ifndef LINKEDLIST_H */

src/linkedlist.c

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+#include "linkedlist.h"
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+
+typedef struct Node {
+    void *data;
+    struct Node *next;
+} Node;
+
+struct LinkedList {
+    size_t len;
+    size_t elem_size;
+    Node *head;
+};
+
+LinkedListErr linkedlist_create(LinkedList **out, size_t elem_size) {
+    if (out == NULL) {
+        return LLIST_NULL;
+    }
+
+    if (elem_size < 1) {
+        return LLIST_INVALID_SIZE;
+    }
+
+    LinkedList *new = malloc(sizeof(LinkedList));
+    if (new == NULL) {
+        return LLIST_ALLOC;
+    }
+    new->elem_size = elem_size;
+    new->len = 0;
+    new->head = NULL;
+
+    *out = new;
+    return LLIST_OK;
+}
+
+LinkedListErr linkedlist_destroy(LinkedList *ll) {
+    if (ll == NULL) {
+        return LLIST_NULL;
+    }
+
+    Node *current = ll->head;
+    if (ll->head == NULL) {
+        free(ll);
+        return LLIST_OK;
+    }
+    while(current->next != NULL) {
+        free(current->data);
+        Node *next = current->next;
+        free(current);
+        current = next;
+    }
+    free(current->data);
+    free(current);
+    free(ll);
+
+    return LLIST_OK;
+}
+
+LinkedListErr linkedlist_append(LinkedList *ll, void *data) {
+    if (ll == NULL) {
+        return LLIST_NULL;
+    }
+
+    if (data == NULL) {
+        return LLIST_NULL_ARG;
+    }
+
+    Node *current = ll->head;
+    if (ll->head != NULL) {
+        while(current->next != NULL) {
+            current = current->next;
+        }
+    }
+
+    Node *new_node = malloc(sizeof(Node));
+    if (new_node == NULL) {
+        return LLIST_ALLOC;
+    }
+
+    new_node->data = malloc(ll->elem_size);
+    if (new_node->data == NULL) {
+        free(new_node);
+        return LLIST_ALLOC;
+    }
+
+    memcpy(new_node->data, data, ll->elem_size);
+    new_node->next = NULL;
+    
+    if (ll->head == NULL) {
+        ll->head = new_node;
+    } else {
+        current->next = new_node;
+    }
+    ll->len = ll->len + 1;
+
+    return LLIST_OK;
+}
+
+LinkedListErr linkedlist_get(const LinkedList *ll, size_t index, void *out) {
+    if (ll == NULL) {
+        return LLIST_NULL;
+    }
+
+    if (out == NULL) {
+        return LLIST_NULL_ARG;
+    }
+
+    if (index >= ll->len) {
+        return LLIST_OUT_OF_BOUNDS;
+    }
+
+    Node *current = ll->head;
+    for (size_t i = 0; i < index; i++) {
+        current = current->next;
+    }
+
+    memcpy(out, current->data, ll->elem_size);
+
+    return LLIST_OK;
+}

tests/CMakeLists.txt

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+find_package(cmocka REQUIRED)
+
+add_executable(test_linkedlist
+    test_linkedlist.c
+)
+
+target_link_libraries(test_linkedlist
+    PRIVATE
+        linkedlist
+        cmocka
+)
+
+target_compile_options(test_linkedlist PRIVATE
+    -fsanitize=address
+)
+
+target_link_options(test_linkedlist PRIVATE
+    -fsanitize=address
+)
+
+add_test(NAME linkedlist_tests
+         COMMAND test_linkedlist)
+

tests/test_linkedlist.c

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+#include "linkedlist.h"
+#include <stdlib.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <setjmp.h>
+#include <cmocka.h>
+
+static void linkedlist_test_append(void **state) {
+    (void) state;
+
+    LinkedList *ll;
+    linkedlist_create(&ll, sizeof(int));
+    for (int i = 10; i < 13; i++) {
+        linkedlist_append(ll, &i);
+    }
+    for (int i = 0; i < 3; i++) {
+        int n;
+        linkedlist_get(ll, i, &n);
+        assert_int_equal(n, i + 10);
+    }
+    linkedlist_destroy(ll);
+}
+
+int main(void) {
+    const struct CMUnitTest tests[] = {
+        cmocka_unit_test(linkedlist_test_append),
+    };
+
+    return cmocka_run_group_tests(tests, NULL, NULL);
+}