使用Maps和make_pair编译错误
Compile error with Maps and make_pair
我正在复习几个关键的STL概念。我写了下面的程序来理解std::pair
和maps
的工作,但是我得到了一个严重的编译错误。尝试添加所有的头,但无法找出什么错误到目前为止。请帮助。
void testMaps()
{
DB_Type phoneDb;
PhoneInfoList_Type v1(8);
PhoneInfo_Type(*phoneInfoGenerator)() = phoneInfoGen;
DBIT_Type it;
PhoneInfoList_Type::iterator phit;
int i = 0, j = 0;
for (phit = v1.begin(); phit != v1.end(); ++phit)
{
v1.push_back(phoneInfoGen());
}
for (phit = v1.begin(); phit != v1.end(); ++phit)
{
phoneDb.insert(*phit);
}
int choice;
std::cout << "Enter choice 0. Search by name, 1. Search by no., 2. Exitn";
while (1)
{
switch (choice)
{
case 0:
{
std::cout << "Enter name:";
std::string name;
std::cin >> name;
DBIT_Type it = std::find(phoneDb.begin(), phoneDb.end(), name);
if (it != phoneDb.end())
{
std::cout <<"n Phone no of " << name << "is " << it->second << "n";
}
else
{
std::cout << "Name not foundn";
}
}break;
case 1:
{
std::cout << "Enter phone no:";
int ph;
std::cin >> ph;
DBIT_Type it = std::find(phoneDb.begin(), phoneDb.end(), ph);
if (it != phoneDb.end())
{
std::cout << "n Name of person with phone no " << ph << "is " << it->first << "n";
}
else
{
std::cout << "Name not foundn";
}
}
break;
default:
break;
}
}
}
得到的编译错误:
warning C4244: 'argument' : conversion from 'time_t' to 'unsigned int', possible loss of data
1>c:program files (x86)microsoft visual studio 12.0vcincludexutility(3026): error C2678: binary '==' : no operator found which takes a left-hand operand of type 'std::pair<const _Kty,_Ty>' (or there is no acceptable conversion)
1> with
1> [
1> _Kty=std::string
1> , _Ty=int
1> ]
1> c:program files (x86)microsoft visual studio 12.0vcincludesystem_error(410): could be 'bool std::operator ==(const std::error_condition &,const std::error_code &) throw()'
1> c:program files (x86)microsoft visual studio 12.0vcincludesystem_error(402): or 'bool std::operator ==(const std::error_code &,const std::error_condition &) throw()'
1> c:program files (x86)microsoft visual studio 12.0vcincludeexception(507): or 'bool std::operator ==(const std::exception_ptr &,std::nullptr_t)'
1> c:program files (x86)microsoft visual studio 12.0vcincludeexception(502): or 'bool std::operator ==(std::nullptr_t,const std::exception_ptr &)'
1> c:program files (x86)microsoft visual studio 12.0vcincludeexception(497): or 'bool std::operator ==(const std::exception_ptr &,const std::exception_ptr &)'
1> while trying to match the argument list '(std::pair<const _Kty,_Ty>, const std::string)'
1> with
1> [
1> _Kty=std::string
1> , _Ty=int
1> ]
有两个错误
-
第一个在这一行:
DBIT_Type it = std::find(phoneDb.begin(), phoneDb.end(), name);
map中的元素类型为
std::pair
,包含键(名称)和值(电话号码)。如果您想使用std::find()
,您需要为它提供您正在寻找的值对,而不仅仅是键。可以通过使用
std::map::find()
来查找密钥:DBIT_Type it = phoneDb.find(name);
-
第二个在这一行:
DBIT_Type it = std::find(phoneDb.begin(), phoneDb.end(), ph);
这个操作失败了,因为
ph
是int
,但是映射的键是std::string
。您显然试图通过其值(电话号码)而不是通过其键(名称)搜索元素。