Global vs Static in C++

Key Differences

Aspect	Global Variable	Static Variable
Scope	Accessible throughout program	Limited to file, function, or class scope
Visibility	Shared across files (extern)	Restricted to declaring scope
Lifetime	Entire program duration	Entire program duration

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Example Code

Global Variable

// globals.cpp
int globalVar = 42; // Global variable

// main.cpp
#include <iostream>
extern int globalVar; // Declaration for the global variable from another file

void modifyGlobal() {
    globalVar++; // Accessible across files
}

int main() {
    modifyGlobal();
    std::cout << "Global Variable: " << globalVar << std::endl; // Prints: 43
    return 0;
}

File-Scope Static Variable

#include <iostream>

static int staticVar = 10; // File-scope static

void modifyStatic() {
    staticVar++; // Accessible only within this file
}

int main() {
    modifyStatic();
    std::cout << "Static Variable: " << staticVar << std::endl; // Prints: 11
    return 0;
}

Function-Scope Static Variable

#include <iostream>

void counter() {
    static int count = 0; // Retains value across calls
    count++;
    std::cout << "Count: " << count << std::endl;
}

int main() {
    counter(); // Prints: 1
    counter(); // Prints: 2
    return 0;
}