What is the difference between local variables and global variables of a C++ function?

C The difference between local variables and global variables: Visibility: Local variables are limited to the defining function, while global variables are visible throughout the program. Memory allocation: local variables are allocated on the stack, while global variables are allocated in the global data area. Scope: Local variables are within a function, while global variables are throughout the program. Initialization: Local variables are initialized when a function is called, while global variables are initialized when the program starts. Recreation: Local variables are recreated on every function call, while global variables are created only when the program starts.

Local variables and global variables of C functions: big difference

In C, there are important differences between local variables and global variables. Understand these The distinction is critical to writing efficient, maintainable code.

Local variables

• are defined within a function and are only visible within the function scope.
• Created when the function is called and destroyed when the function returns.
• Local variables will be recreated every time the function is called.

Sample code:

void myFunction() {
    int localVariable = 5; // 局部变量
    // ... 使用 localVariable
}

int main() {
    myFunction();
    // localVariable 无法访问，因为它不在 main() 函数的范围内
}

Global variables

• are defined outside the function and are visible throughout the entire program.
• Created when the program starts and destroyed when the program terminates.
• Global variables are visible to all functions in the program.

Sample code:

int globalVariable = 10; // 全局变量

void myFunction() {
    // ... 使用 globalVariable
}

int main() {
    // ... 使用 globalVariable
}

Difference

Features	Local variables	Global variables
Visibility	Limited to the function in which they are defined	Entire program
Life cycle	During function call	During program running
Memory allocation	On the stack	In the global data area
Scope	In the function	In the entire program
Initialization	When the function is called	When the program starts
Recreate	Every time the function When called	Only when the program starts

Actual case

Examples of local variables

In the following example , the local variable name is only used within the greet() function, and is recreated each time the function is called:

void greet(std::string name) {
    std::cout << "Hello, " << name << "!" << std::endl;
}

int main() {
    greet("John");
    greet("Mary"); // 局部变量 name 将重新创建
}

Example of global variables

In the following example, the global variable g_count is visible program-wide and is updated every time the function is called:

int g_count = 0; // 全局变量

void incrementCount() {
    g_count++;
}

int main() {
    incrementCount();
    std::cout << "Count: " << g_count << std::endl; // 输出 1

    incrementCount();
    std::cout << "Count: " << g_count << std::endl; // 输出 2
}

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