[英]C++ compile time error: expected identifier before numeric constant
I have read other similar posts but I just don't understand what I've done wrong. 我读过其他类似的文章,但我只是不明白自己做错了什么。 I think my declaration of the vectors is correct.
我认为我对向量的声明是正确的。 I even tried to declare without size but even that isn't working.What is wrong??
我什至试图声明没有大小,但那还是行不通。怎么了? My code is:
我的代码是:
#include <vector>
#include <string>
#include <sstream>
#include <fstream>
#include <cmath>
using namespace std;
vector<string> v2(5, "null");
vector< vector<string> > v2d2(20,v2);
class Attribute //attribute and entropy calculation
{
vector<string> name(5); //error in these 2 lines
vector<int> val(5,0);
public:
Attribute(){}
int total,T,F;
};
int main()
{
Attribute attributes;
return 0;
}
You cannot do this: 你不能做这个:
vector<string> name(5); //error in these 2 lines
vector<int> val(5,0);
in a class outside of a method. 在方法之外的类中。
You can initialize the data members at the point of declaration, but not with ()
brackets: 您可以在声明时初始化数据成员,但不能使用
()
括号进行初始化:
class Foo {
vector<string> name = vector<string>(5);
vector<int> val{vector<int>(5,0)};
};
Before C++11, you need to declare them first, then initialize them eg in a contructor 在C ++ 11之前,您需要先声明它们,然后在例如构造器中对其进行初始化
class Foo {
vector<string> name;
vector<int> val;
public:
Foo() : name(5), val(5,0) {}
};
Initializations with (...)
in the class body is not allowed. 不允许在类主体中使用
(...)
进行初始化。 Use {..}
or = ...
. 使用
{..}
或= ...
Unfortunately since the respective constructor is explicit
and vector
has an initializer list constructor, you need a functional cast to call the wanted constructor 不幸的是,由于相应的构造函数是
explicit
并且vector
具有初始化列表构造函数,因此您需要进行函数转换以调用所需的构造函数
vector<string> name = decltype(name)(5);
vector<int> val = decltype(val)(5,0);
As an alternative you can use constructor initializer lists 或者,您可以使用构造函数初始化器列表
Attribute():name(5), val(5, 0) {}
由于您的编译器可能还不支持所有C ++ 11(支持相似的语法),因此会出现这些错误,因为您必须在构造函数中初始化类成员:
Attribute() : name(5),val(5,0) {}
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