没有合适的用户定义转换

Question

在'CompaniesMap.h'中：

class CompaniesMap
{
public:
...
    // The companies map
    map<string, CompanyP> companies;
};

typedef map<string, CompanyP>::iterator map_it;

在'CompaniesMap.cpp'中：

string* CompaniesMap::displayCompaniesList() const
{
    string* compList = new string[companies.size() + 1];        // We add 1 so we can start with the [1] index for simplicity

    // Check if 'companies' is empty
    if (companies.empty())
    {
        cout << "No companies in the database." << endl;
        return nullptr;
    }

    for (map_it it = companies.begin(), int i = 1; it != companies.end(); ++it, i++)
    {
        cout << "   " << i << ") " << it->first << endl;
        compList[i] = it->first;
    }
}

Visual Studio在companies.begin()下显示一条红线，并显示以下错误消息：

我已尝试将代码从map_it it =更改为map<string, CompanyP>::iterator但我仍然收到此错误

我在main.cpp中使用相同的代码，但决定将其移至单独的类，我包含相同的相关标题，但仍然看到此错误。当我尝试构建时，我从这个文件中得到了不同的错误：

1>d:\asaf\c\vs\hw5\hw5\hw5\companiesmap.cpp(66): error C2062: type 'int' unexpected
1>d:\asaf\c\vs\hw5\hw5\hw5\companiesmap.cpp(66): error C2065: 'i' : undeclared identifier
1>d:\asaf\c\vs\hw5\hw5\hw5\companiesmap.cpp(66): error C2143: syntax error : missing ';' before ')'
1>d:\asaf\c\vs\hw5\hw5\hw5\companiesmap.cpp(67): error C2143: syntax error : missing ';' before '{'
1>d:\asaf\c\vs\hw5\hw5\hw5\companiesmap.cpp(68): error C2065: 'i' : undeclared identifier
1>d:\asaf\c\vs\hw5\hw5\hw5\companiesmap.cpp(69): error C2065: 'i' : undeclared identifier

Answer 1

displayCompaniesList是const函数，这意味着您无法对类中定义的变量进行任何更改。

因此，{p> companies将是const std::map<std::string, CompanyP>，而不是std::map<std::string, CompanyP>，因此您必须相应地更改迭代器：

std::map<std::string, CompanyP>::const_iterator it = companies.begin();

//Or even better if you use C++11
auto it = companies.begin();