Declaring a structure with no members in C language

In C programming, it is possible to declare a structure with no members. This creates what is known as an empty structure or zero-size structure. While not commonly used in practice, understanding this concept helps in grasping how C handles structure memory allocation.

Syntax

struct structure_name {
    // No members declared
};

Size of Empty Structure

When a structure is declared with no members, its size is implementation-defined. In most C compilers, the size of an empty structure is 0 bytes, but some compilers may assign a minimal size (like 1 byte) to ensure each structure instance has a unique address in memory.

Example

Here's a complete program demonstrating an empty structure −

#include <stdio.h>

// Structure with no members
struct empty_struct {
};

int main() {
    // Declaring structure variable
    struct empty_struct T;
    
    printf("Size of empty structure: %zu bytes
", sizeof(T));
    printf("Size using struct name: %zu bytes
", sizeof(struct empty_struct));
    
    return 0;
}

Size of empty structure: 0 bytes
Size using struct name: 0 bytes

Practical Considerations

• Memory allocation: Empty structures consume no memory but still have valid addresses
• Compiler behavior: Different compilers may handle empty structures differently
• Usage: Rarely used in practice, mainly for placeholder purposes or advanced template programming

Key Points

• Empty structures are legal in C but have limited practical use
• The sizeof() operator returns 0 for most implementations
• Each instance of an empty structure still has a unique memory address

Conclusion

While C allows declaring structures with no members, resulting in zero-size structures, this feature is rarely used in practical programming. Understanding this concept helps in comprehending C's flexible structure definition capabilities.