---
title: "1.25 Basic Storage-Class Specifiers"
description: "Storage-class specifiers affect the storage duration, linkage, or declaration behavior of an object or function. The commonly used C storage-class specifiers are `auto`, `register`, `static`, and `extern`. ``` #include int global_value = 10; static int file_value = 20; int main()…"
url: "https://edcret.in/docs/c-programming/basic-refreshers/1-25-basic-storage-class-specifiers/"
updated: "2026-09-06"
category: C Programming / Basic Refreshers
---

# 1.25 Basic Storage-Class Specifiers

Storage-class specifiers affect the storage duration, linkage, or declaration behavior of an object or function. The commonly used C storage-class specifiers are `auto`, `register`, `static`, and `extern`.

```
#include <stdio.h>

int global_value = 10;

static int file_value = 20;

int main()
{
    auto int local_value = 30;
    register int counter = 40;

    printf("%d\n", global_value);
    printf("%d\n", file_value);
    printf("%d\n", local_value);
    printf("%d\n", counter);

    return 0;
}
```

### Example Output

```
10
20
30
40
```

### Explanation

`auto` declares an object with automatic storage duration. For a block-scope variable, automatic storage duration is already the default:

```
auto int local_value = 30;
```

`register` requests that the implementation keep the object in a processor register when appropriate:

```
register int counter = 40;
```

The compiler is not required to place the object in a register.

`static` has different effects depending on where it appears. At file scope, it gives an object or function internal linkage:

```
static int file_value = 20;
```

`extern` declares an object or function that is defined elsewhere or later in the program:

```
extern int global_value;
```

### Storage-Class Specifiers

| Specifier | Typical use | Main effect |
| --- | --- | --- |
| `auto` | Block-scope objects | Automatic storage duration |
| `register` | Block-scope objects | Requests register storage |
| `static` | Objects and functions | Static storage duration or internal linkage, depending on scope |
| `extern` | Objects and functions | Declares an entity with external linkage or refers to an existing definition |

The meaning of `static` depends on declaration scope, so it is covered separately in the storage-class and linkage section.