# Referensi Cepat C *Sintaks, pointer, manajemen memori, esensial standard library* > Source: C Standard Library (cppreference.com) · MIT ## Dasar ### Hello World ``` #include int main(void) { printf("Hello, World!\n"); return 0; } ``` ### Kompilasi & Jalankan ``` gcc -o app main.c # compile gcc -Wall -Wextra -std=c17 main.c # strict ./app # run ``` ### Komentar ``` // single-line comment (C99+) /* multi-line comment */ ``` ## Tipe Data ### Tipe Primitif | Command | Description | |---------|-------------| | `char` | 1 byte, karakter atau integer kecil | | `short` | Minimal 16 bit | | `int` | Minimal 16 bit (biasanya 32) | | `long` | Minimal 32 bit | | `long long` | Minimal 64 bit (C99+) | | `float` | IEEE-754 32-bit | | `double` | IEEE-754 64-bit | | `_Bool / bool` | `0` atau `1` (gunakan `` untuk `bool`) | ### Tipe Lebar Tetap (stdint.h) | Command | Description | |---------|-------------| | `int8_t, uint8_t` | Tepat 8-bit bertanda / tak bertanda | | `int16_t, uint16_t` | Tepat 16-bit | | `int32_t, uint32_t` | Tepat 32-bit | | `int64_t, uint64_t` | Tepat 64-bit | | `size_t` | Tak bertanda, hasil `sizeof` | ### Type Casting ``` int i = (int)3.14; // explicit cast double d = (double)5 / 2; // 2.5, not 2 char c = (char)65; // 'A' ``` ## Control Flow ### If / Else ``` if (x > 0) { printf("positive\n"); } else if (x == 0) { printf("zero\n"); } else { printf("negative\n"); } ``` ### Switch ``` switch (choice) { case 1: printf("one\n"); break; case 2: printf("two\n"); break; default: printf("other\n"); } ``` ### Loop ``` for (int i = 0; i < 10; i++) { } while (condition) { } do { } while (condition); ``` ### Pernyataan Lompat | Command | Description | |---------|-------------| | `break` | Keluar dari loop atau switch terdalam | | `continue` | Lanjut ke iterasi berikutnya | | `return` | Keluar fungsi dengan nilai opsional | | `goto label` | Lompat ke label (gunakan seperlunya) | ## Fungsi ### Deklarasi & Definisi ``` int add(int a, int b); // prototype int add(int a, int b) { return a + b; } ``` ### Function Pointer ``` int (*op)(int, int) = add; int result = op(3, 4); // calls add(3, 4) typedef int (*MathFn)(int, int); MathFn fn = add; ``` ### Fungsi Static ``` // visible only within this translation unit static int helper(int x) { return x * 2; } ``` ## Pointer ### Dasar Pointer ``` int x = 42; int *p = &x; // p points to x printf("%d\n", *p); // dereference: 42 *p = 100; // x is now 100 ``` ### Aritmatika Pointer ``` int arr[] = {10, 20, 30}; int *p = arr; printf("%d\n", *(p + 1)); // 20 printf("%d\n", p[2]); // 30 (same as *(p+2)) ``` ### Pola Pointer Umum | Command | Description | |---------|-------------| | `int *p = NULL` | Pointer null (selalu inisialisasi) | | `void *` | Pointer generik (harus di-cast untuk digunakan) | | `const int *p` | Pointer ke konstanta (nilai tidak bisa diubah) | | `int *const p` | Pointer konstanta (pointer tidak bisa di-reassign) | | `int **pp` | Pointer ke pointer (double indirection) | ## Array & String ### Array ``` int nums[5] = {1, 2, 3, 4, 5}; int matrix[2][3] = {{1,2,3}, {4,5,6}}; int len = sizeof(nums) / sizeof(nums[0]); ``` ### Fungsi String (string.h) | Command | Description | |---------|-------------| | `strlen(s)` | Panjang (tidak termasuk null terminator) | | `strcpy(dst, src)` | Salin string (tidak aman, lebih baik `strncpy`) | | `strncpy(dst, src, n)` | Salin maksimal n karakter | | `strcat(dst, src)` | Gabungkan string | | `strcmp(a, b)` | Bandingkan: 0 jika sama, <0 atau >0 jika tidak | | `strchr(s, c)` | Temukan kemunculan pertama karakter | | `strstr(haystack, needle)` | Temukan substring | ### String Literal ``` char greeting[] = "hello"; // mutable array const char *msg = "world"; // pointer to literal char buf[64]; snprintf(buf, sizeof(buf), "%s %s", greeting, msg); ``` ## Struct ### Definisi & Penggunaan ``` struct Point { double x; double y; }; struct Point p = {1.0, 2.0}; printf("(%g, %g)\n", p.x, p.y); ``` ### Typedef ``` typedef struct { char name[50]; int age; } Person; Person p = {"Alice", 30}; ``` ### Pointer ke Struct ``` void set_age(Person *p, int age) { p->age = age; // arrow operator } ``` ### Enum & Union ``` enum Color { RED, GREEN, BLUE }; union Data { int i; float f; char c; }; // union members share the same memory ``` ## Manajemen Memori ### Alokasi Dinamis (stdlib.h) ``` int *arr = malloc(10 * sizeof(int)); if (arr == NULL) { /* handle error */ } arr = realloc(arr, 20 * sizeof(int)); free(arr); arr = NULL; // avoid dangling pointer ``` ### Fungsi Alokasi | Command | Description | |---------|-------------| | `malloc(size)` | Alokasi memori tanpa inisialisasi | | `calloc(count, size)` | Alokasi dan inisialisasi nol | | `realloc(ptr, size)` | Ubah ukuran blok yang sudah dialokasi | | `free(ptr)` | Bebaskan memori yang dialokasi | ### Kesalahan Umum | Command | Description | |---------|-------------| | `Memory leak` | Lupa memanggil `free()` pada memori yang dialokasi | | `Double free` | Memanggil `free()` dua kali pada pointer yang sama | | `Dangling pointer` | Menggunakan pointer setelah `free()` — set ke NULL | | `Buffer overflow` | Menulis melampaui batas alokasi | ## File I/O ### Membaca File ``` FILE *f = fopen("data.txt", "r"); if (!f) { perror("open"); return 1; } char line[256]; while (fgets(line, sizeof(line), f)) printf("%s", line); fclose(f); ``` ### Menulis ke File ``` FILE *f = fopen("out.txt", "w"); fprintf(f, "value: %d\n", 42); fputs("hello\n", f); fclose(f); ``` ### Mode File | Command | Description | |---------|-------------| | `"r"` | Baca (file harus ada) | | `"w"` | Tulis (potong atau buat baru) | | `"a"` | Tambahkan (buat jika tidak ada) | | `"rb", "wb"` | Baca / tulis binary | | `"r+"` | Baca dan tulis (file harus ada) | ## Preprocessor ### Direktif ``` #include // system header #include "myheader.h" // local header #define PI 3.14159 #define MAX(a, b) ((a) > (b) ? (a) : (b)) ``` ### Kompilasi Kondisional ``` #ifdef DEBUG printf("debug: x = %d\n", x); #endif #ifndef HEADER_H /* include guard */ #define HEADER_H /* ... */ #endif ``` ### Macro Umum | Command | Description | |---------|-------------| | `__FILE__` | Nama file sumber saat ini | | `__LINE__` | Nomor baris saat ini | | `__func__` | Nama fungsi saat ini (C99+) | | `__DATE__` | String tanggal kompilasi | | `NULL` | Konstanta pointer null | | `sizeof(x)` | Ukuran tipe atau variabel dalam byte |