Question

If a function is defined as static, it means

• A. The value returned by the function does not change
• B. all the variable declared inside the function automatically will be assigned initial value of zero
• C. It should be called only within the same source code program file.
• D. None of the other choices as it is wrong to add static prefix to a function

Hint:

Using static on functions is a common and excellent practice in C programming to hide helper functions from the global scope, effectively achieving a form of encapsulation.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The topic of this question is Scope and Linkage in Programming (specifically in C or C++). The keyword `static` is one of the most versatile and sometimes confusing keywords in these languages because its meaning changes depending on where it is applied (to a local variable, a global variable, or a function). This question specifically asks about its effect when applied to a function declaration.
Step 2: Key Formulas and approach:
The approach involves understanding the concept of "Translation Units" and "Linkage."
1. External Linkage: By default, functions are visible to all files in a project.
2. Internal Linkage: Using `static` limits visibility to the current file.
We evaluate the options to see which one correctly describes the restriction on visibility and accessibility caused by the `static` prefix on a function.
Step 3: Detailed Explanation:}

In a large software project consisting of multiple source files (.c or .cpp files), the compiler processes each file individually into an object file.

Normally, if you define a function in `file1.c`, you can call it from `file2.c` by using an `extern` declaration. This is known as external linkage.

However, if you define a function as `static void myFunc() { ... }`, you are telling the compiler that this function has internal linkage.

This means the function is private to that specific file. It cannot be seen or accessed by the linker when it tries to resolve function calls from other files.

This is a form of encapsulation used to prevent "namespace pollution" or naming conflicts. For example, two different files can both have a `static` function named `init()` without interfering with each other.

Option A is incorrect because `static` doesn't affect the return value. Option B is incorrect because that describes static variables, not the function itself.

Step 4: Final Answer:
A static function is restricted to internal linkage, meaning it can only be called from within the same source code file where it is defined.

Answer 2

Consider a small two-file program to see what static actually restricts. Suppose file1.c contains:
static void helper() { }
and file2.c contains a call to helper(); along with a declaration extern void helper(); at the top.

Normally, if helper were declared without static, file2.c's extern declaration would let the linker find helper's definition in file1.c's compiled object file, and the program would build successfully.
But because helper is declared static in file1.c, its linkage becomes internal rather than external. When the linker processes file2.c's object file and looks for a definition of helper to satisfy the extern declaration, it will not find one, since the static definition in file1.c is deliberately hidden from every other translation unit.
The result is a linker error such as an undefined reference to helper, even though the function clearly exists and is correctly written inside file1.c.

This demonstrates concretely that static does not affect what the function does when called; it only affects where the function is allowed to be called from, restricting it strictly to the file where it is defined.

Therefore, the correct answer is It should be called only within the same source code program file.