# V3555\. AUTOSAR\. The 'static' storage class specifier should be used in all declarations of functions that have internal linkage\.

This diagnostic rule is based on the software development guidelines developed by [AUTOSAR](https://www.autosar.org/) \(AUTomotive Open System ARchitecture\)\.

A function declared once with 'internal linkage', when redeclared or defined, will also have 'internal linkage'\. This may not be obvious to developers, and therefore you should explicitly specify the 'static' specifier in each declaration and definition\.

The following code does not comply with the rule, since the definition does not reflect the internal linkage type specified in the 'foo' function declaration with the 'static' keyword:

```cpp
static void foo(int x);
void foo(int x)
{
  ....
}
```

According to the rule, the code fragment should be as follows:

```cpp
static void foo(int x);
static void foo(int x)
{
  ....
}
```

In the example below, the definition of the 'foo' function with the 'extern' storage class specifier does not specify the 'external linkage' type, as it might seem\. The linkage type remains 'internal linkage':

```cpp
static void foo(int x);
extern void foo(int x)
{
  ....
}
```

The correct option:

```cpp
extern void foo(int x);
extern void foo(int x)
{
  ....
}
```