出乎意料的是不是所有的控制路徑都返回一個值？

Question

我目前正在 C++ 中編寫一個程序，並創建了一個名為 parseText 的 function。 當我運行此 function 時，我收到警告“並非所有控制路徑都返回值”，但是在多次查看此代碼后，我無法找出發生這種情況的原因。 這是一個不正確的錯誤還是我錯過了什么。

int parseText(std::string line, std::string *posResponses) {
    for (int x = 0; x < line.length(); x++) {
        line.at(x) = toupper(line.at(x));
    }
    if (line == "HELP") {
        runHelp(3);
        return 0;           //returns 0 if user entered invalid response and needs to repeat the code
    }else if (line == "QUIT") {
        return 2;           //returns 2 if user wants to quit 
    }
    if (posResponses->size() == 1 && posResponses[0] == line) {
        return 1;           //returns 1 if there was a valid response               
    }else if (posResponses[0] == "int") {
        int x = posResponses[1].size();
        for (int i = 0; i <= x; i++) {
            if (posResponses[1].at(i) < 48 || posResponses[1].at(i) > 57) {
                return 0;   //returns 0 if user entered invalid response and needs to repeat the code
            }
            return 1;       //returns 1 if there was a valid response
        }
    }
    else{
        int x = posResponses->size();
        for (int i = 0; i <= x; i++) {
            if (posResponses[i] == line) {
                return 1;   //returns 1 if there was a valid response
            }
        }
        return 0;           //returns 0 if user entered invalid response and needs to repeat the code
    }
}

Answer 1

在這個if分支

} else if (posResponses[0] == "int") {
    int x = posResponses[1].size();
    for (int i = 0; i <= x; i++) {
        if (posResponses[1].at(i) < 48 || posResponses[1].at(i) > 57) {
            return 0;   //returns 0 if user entered invalid response and needs to repeat the code
        }
        return 1;       //returns 1 if there was a valid response
    }
}

如果x被賦值< 0 ，則根本不會進入for循環，那么這個分支就沒有return語句。

也許您確定x在運行時不會為負數，但編譯器必須在編譯時確認所有分支的這一點。

我不確定你的意圖，你可能想要

} else if (posResponses[0] == "int") {
    if (posResponses[1].size() == 0 || posResponses[1].at(0) < 48 || posResponses[1].at(0) > 57) {
        return 0;   //returns 0 if user entered invalid response and needs to repeat the code
    }
    return 1;       //returns 1 if there was a valid response
}