Question

我试图将字符串与结构向量中的struct元素进行比较。我已正确创建了向量，但似乎无法使if语句生效。它总是返回true。这样做的正确方法是什么？的结构：

struct customer{
    string name;
    string phoneNumber;
    string addressLine1;
    string addressLine2;
};

循环迭代包含if语句的向量：

cout<<"Input customer's phone number: ", cin>>phoneNumber, cout<<endl;
int foundIndex = 0;
bool found = false;
for(int it = 1; it < customers.size(); it++){
    if(phoneNumber.compare(customers[it].phoneNumber)){
        cout<<"Found at "<<foundIndex<<endl;
        cout<<"Name: "<<customers[foundIndex].name<<endl;
        cout<<"Phone Number: "<<customers[foundIndex].phoneNumber<<endl;
        cout<<"Address: "<<customers[foundIndex].addressLine1<<endl<<"                 "<<customers[foundIndex].addressLine2<<endl;
        found = true;
        break;
    }
}

从CSV填充Vector的功能：

vector<customer> readFile(void){
    string name;
    string phoneNumber;
    string addressLine1;
    string addressLine2;
    vector<customer> customers;
    vector<string> temper;
    customer temp;
    fstream ioFile;
    ioFile.open("customers.csv", fstream::in | fstream::out | fstream::app);
    while (!ioFile.eof()){
        getline(ioFile, name);
        temper = split(name);
        temp.name = temper[0];
        temp.phoneNumber = temper[1];
        temp.addressLine1 = temper[2];
        temp.addressLine2 = temper[3];
        customers.push_back(temp);
    }

    ioFile.close();
    return customers;
}

Answer 1

标准库提供std::find_if功能，使用自定义谓词搜索容器。

std::vector<customer> customers;

auto result = std::find_if(
    customers.begin(),
    customers.end(),
    [&phoneNumber](customer const& c) {
        return c.phoneNumber == phoneNumber;
    }
);

if (result != customers.end()) {
    std::cout << *result << '\n';
}

Answer 2

通常，您编写的代码应该有效，但您有一些问题需要监督

Vector从索引0开始。所以你应该从索引0开始迭代

您正在初始化foundIndex = 0但findIndex永远不会更改（为此代码片段没有必要。我修改了你的代码。它现在应该工作

cout<<"Input customer's phone number: ", cin>>phoneNumber, cout<<endl;
bool found = false;
for(int it = 0; it < customers.size(); it++){
        if(phoneNumber.compare(customers[it].phoneNumber){
            cout<<"Found at "<<it<<endl;
            cout<<"Name: "<<customers[it].name<<endl;
            cout<<"Phone Number: "<<customers[it].phoneNumber<<endl;
            cout<<"Address: "<<customers[it].addressLine1<<endl<<"                 "<<customers[it].addressLine2<<endl;
            found = true;
            break;
        }
}

你是否认识到我使用“它”？如果你需要foundIndex 添加

foundIndex=it;

之前

    break;

在不改变FoundIndex的情况下，您将始终获得第一个条目。

Answer 3

替换

phoneNumber.compare（客户[它] .phoneNumber）

通过

phoneNumber.compare（customers [it] .phoneNumber）== 0

说明：compare是一个度量，如果不存在差异则返回零。因此，例如，＆＃34; Foo＆＃34; .compare（＆＃34; Bar＆＃34;）＆gt; 0，因此评估为真，而＆＃34; Foo＆＃34; .compare（＆＃34; Foo＆＃34;）= 0如果用作布尔值，将评估为false。

参见http://www.cplusplus.com/reference/string/string/compare/

中的示例

Answer 4

如果字符串相等，

std::string::compare会返回0。 phoneNumber.compare(customers[it].phoneNumber)对于匹配数字将为false，对于错误的数字为true。只需使用==运算符：

for (size_t i = 0; i < customers.size(); ++i) 
{
    if (customers[i].phoneNumber == phoneNumber) 
    {
        std::cout << "Found: " << customers[i].name;
        break;
    }
}

要改进代码，您可以使用标准库中的std::find_if模板：

auto it = std::find_if(begin(customers), end(customers),
                      [&phoneNumber](const customer& c) { 
                          return c.phoneNumber == phoneNumber; 
                      });

if (it != end(customers))
    std::cout << it->name;

搜索字符串C ++的结构向量

4 个答案: