在C ++中声明if-else块中的变量 [英] Declaring a variable in an if-else block in C++

问题描述

我正在尝试在if-else块中声明一个变量，如下所示：

I'm trying to declare a variable in an if-else block as follows:

int main(int argc, char *argv[]) {

    if (argv[3] == string("simple")) {
        Player & player = *get_Simple();
    } else if (argv[3] == string("counting")) {
        Player & player = *get_Counting();
    } else if (argv[3] == string("competitor")) {
        Player & player = *get_Competitor();
    }

    // More code
}

但是，当我尝试编译时，我遇到以下错误：

But, I'm getting the following errors when I try to compile:

driver.cpp：38：错误：未使用的变量
'player'
driver.cpp：40：错误：
未使用的变量'player'

driver.cpp：42：错误：未使用的变量
'player'< br> driver.cpp：45：错误：
'玩家'未在此
范围内声明

driver.cpp:38: error: unused variable ‘player’
driver.cpp:40: error: unused variable ‘player’
driver.cpp:42: error: unused variable ‘player’
driver.cpp:45: error: ‘player’ was not declared in this scope

有什么想法吗？

推荐答案

你的问题是每个if / else if块的播放器超出范围。

Your problem is that player falls out of scope in each if / else if block.

您需要在所有if语句之上声明您的变量。

You need to declare your variable above all of the if statements.

但是你不能使用引用，因为你必须立即初始化引用。

But you can't use a reference for that because you must initialize a reference right away.

你可能想要这样的东西：

Instead you probably want something like this:

int main(int argc, char *argv[]) {

    Player * pPlayer = NULL;
    if (argv[3] == string("simple")) {
        pPlayer = get_Simple();
    } else if (argv[3] == string("counting")) {
        pPlayer = get_Counting();
    } else if (argv[3] == string("competitor")) {
        pPlayer = get_Competitor();
    }

    //Then if you really want to...
    Player &player = *pPlayer;

}

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