沒有來自“lambda []()-&gt; 的合適的用戶定義轉換<error-type> &quot; 到 &quot; 常量 std::vector <int, std::allocator<int> &gt;&quot;

Question

我嘗試實現 lambda 函數：-

    vector<int> numbers;
    int value = 0;

    cout << "Pushing back...\n";
    while (value >= 0) {
        cout << "Enter number: ";
        cin >> value;
        if (value >= 0)
            numbers.push_back(value);
    }
    print( [numbers]() ->  
    {

        cout << "Vector content: {  ";
        for (const int& num : numbers)
            cout << num << "  ";
        cout << "}\n\n";  


    });

我收到一個錯誤：-

1.Severity  Code    Description Project File    Line    Source  Suppression State
Error (active)  E0312   no suitable user-defined conversion from "lambda []()-><error-type>" to "const std::vector<int, std::allocator<int>>" exists    consoleapplication  C:\Users\insmitr\source\repos\consoleapplication\consoleapplication.cpp 46  IntelliSense    

2.Severity  Code    Description Project File    Line    Source  Suppression State
Error (active)  E0079   expected a type specifier   consoleapplication  C:\Users\insmitr\source\repos\consoleapplication\consoleapplication.cpp 47  IntelliSense

你能在這方面幫助我嗎

Answer 1

問題是print接受一個vector<int>但是在調用print時你傳遞了一個 lambda 並且由於沒有從 lambda 到向量的隱式轉換，你會得到提到的錯誤。

您不一定需要調用print ，因為您可以調用 lambda 本身，如下所示。 另一種方法是print一個函數模板，以便它可以接受任何可調用對象，然后調用傳遞的可調用對象。

int main()
{
    std::vector<int> numbers;
    int value = 0;

    cout << "Pushing back...\n";
    while (value >= 0) {
        cout << "Enter number: ";
        cin >> value;
        if (value >= 0)
            numbers.push_back(value);
    }
//-------------------vvvv------>void added here
    ( [numbers]() -> void 
    {

        cout << "Vector content: {  ";
        for (const int& num : numbers)
            cout << num << "  ";
        cout << "}\n\n";  

//----vv---->note the brackets for calling
    })();
    return 0;
}

演示