How does a lambda expression in a C++ function capture external variables via parameter passing?

C Lambda expressions can capture external variables through parameter passing. The specific steps are as follows: Define a function that accepts a lambda expression as a parameter. Capture external variables in lambda expressions. Pass a lambda expression as a parameter to the function. Call the lambda expression in the function to access the captured external variables.

How Lambda expressions in C functions capture external variables through parameter passing

Lambda expressions are a type of expression in C A convenient way to define anonymous functions. They can capture external variables, making them accessible within function scope. When you need to pass a lambda expression as a parameter to another function, you can capture external variables through parameter passing.

The following steps show how to capture external variables via parameter passing:

#include <iostream>

using namespace std;

// 外部变量
int global_var = 10;

// 接受 lambda 表达式作为参数的函数
void print_captured_var(function<void(int)> lambda) {
    // 在 lambda 表达式中访问捕获的外部变量
    lambda(global_var);
}

int main() {
    // 定义 lambda 表达式，捕获外部变量 global_var
    auto lambda = [](int x) { cout << "捕获的变量：" << x << endl; };

    // 将 lambda 表达式作为参数传递给 print_captured_var 函数
    print_captured_var(lambda);

    return 0;
}

Output:

捕获的变量：10

In this example:

• global_var is an external int variable whose value is initialized to 10.
• print_captured_var The function accepts a function object lambda as a parameter. It will call the function object and pass the value of a captured external variable as an actual parameter.
• lambda A function is a lambda expression that captures the external variable global_var. In a lambda expression, the value of the external variable is printed to standard output. The
• main function passes the lambda expression as a parameter to the print_captured_var function and then calls the function.
• print_captured_var The function prints the value of the captured external variable in the lambda expression, getting the output "Captured variable: 10".

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