Scope, Lifetime & Linkage Differences

Understanding variable storage classes is essential for writing robust C programs:

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Complete Working C Code

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>

/* Global variable: External linkage across entire program */
int globalCounter = 0;

/* Static global: Internal linkage restricted to this file */
static int filePrivateCounter = 100;

void demonstrateStaticLocal() {
    int autoVar = 0;       /* Reinitialized on every function call */
    static int staticVar = 0; /* Initialized ONCE; retains state */

    autoVar++;
    staticVar++;
    globalCounter++;
    filePrivateCounter++;

    printf("autoVar = %d | staticVar = %d | global = %d | staticGlobal = %d\n",
           autoVar, staticVar, globalCounter, filePrivateCounter);
}

int main() {
    printf("Executing function multiple times:\n\n");
    for (int i = 1; i <= 3; i++) {
        printf("--- Call #%d ---\n", i);
        demonstrateStaticLocal();
    }

    return 0;
}

Sample Output

text (ISO Standard)
Copy
Executing function multiple times:

--- Call #1 ---
autoVar = 1 | staticVar = 1 | global = 1 | staticGlobal = 101
--- Call #2 ---
autoVar = 1 | staticVar = 2 | global = 2 | staticGlobal = 102
--- Call #3 ---
autoVar = 1 | staticVar = 3 | global = 3 | staticGlobal = 103

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Complexity Analysis

• Time Complexity: O(1) direct variable access without stack reallocation.
• Memory Allocation: Static and global variables persist in the process's data segment (.data / .bss).

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Related Guides

• Review function execution stacks in Functions in C Programming.
• Master variable declarations in C Programming Basics.