c++ - 返回一个 ifstream 实例以在另一个函数中使用

Question

我将 ifstream 的开头分开，这样我就可以在不重新打开它的情况下循环遍历它，但不确定如何返回它以便它可以在另一个函数中使用。实际上，Npc_B_File 超出了第二个函数的范围。如何返回 ifstream？

void battle_start(char const* P_Name)
{
ifstream Npc_B_File(P_Name);
if(Npc_B_File.fail())
    {
    cout << "could not read file.";
    }

}

 void battle_npc(string npc)
 {

    while(btlcommand != npc)
    {
    Npc_B_File >> btlcommand;
    }
    if(btlcommand == npc_pick_dog)
    Npc_B_File >> btlcommand;

    if(btlcommand == "1" && bat_response == true)
    {
    cout << "You are in" << btlcommand;
    Npc_B_File >> btlcommand;
    bat_response = false;
    }
    if(btlcommand == "2" && bat_response == true)
    {
    cout << "You are in" << btlcommand;
    Npc_B_File >> btlcommand;
    bat_response = false;
    }
    if(btlcommand == "3" && bat_response == true)
    {
    cout << "You are in" << btlcommand;
    Npc_B_File >> btlcommand;
    bat_response = false;
    }
}

Answer 1

选项 1

如果您的编译器和库支持 ifstream 的移动语义，您可以简单地使用:

ifstream battle_start(char const* P_Name)
{
    ifstream Npc_B_File(P_Name);
    if(Npc_B_File.fail())
    {
        cout << "could not read file.";
    }
    return Npc_B_File;
}

int main()
{
    ifstream file(battle_start("filename"));
}

选项 2

对于不为 ifstream 实现移动语义的旧编译器或库，您可以使用:

void battle_start(char const* P_Name, /*out*/ifstream &Npc_B_File)
{
    Npc_B_File.open(P_Name);
    if(Npc_B_File.fail())
    {
        cout << "could not read file.";
    }
}

int main()
{
    ifstream file;
    battle_start("filename", file);
}