错误 - 无法在 C++ 中调用没有对象的成员函数
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Error - cannot call member function without object in C++
提问by user2059901
I get the compile error
我收到编译错误
cannot call member function ‘bool GMLwriter::write(const char*, MyList<User*>&, std::vector<std::basic_string<char> >)' without object
cannot call member function ‘bool GMLwriter::write(const char*, MyList<User*>&, std::vector<std::basic_string<char> >)' without object
when I try to compile
当我尝试编译时
class GMLwriter{
public:
bool write(const char *fn, MyList<User*>& my_vec, vector<string>edges);
};
the function is defined later and called in mainwith
功能被后面定义和被叫main用
GMLwriter::write(argv[3], Users, edges);
GMLwriter::write(argv[3], Users, edges);
Users is declared before with MyList<User*> Users;(MyList is a List ADT and I have a User class) and edges is declared with vector<string>edges
用户之前声明为MyList<User*> Users;（MyList 是一个列表 ADT，我有一个用户类）并且边声明为vector<string>edges
to what objectis this error referring?
什么object是这个错误指？
回答by billz
GMLwriter::writeis not static function of GMLwriter, you need to call it through object. For example:
GMLwriter::write不是 GMLwriter 的静态函数，你需要通过对象调用它。例如：
GMLwriter gml_writer;
gml_writer.write(argv[3], Users, edges);
If GMLwriter::writedoesn't depend on any GMLwriter state(access any member of GMLwriter), you can make it a static member function. Then you could call it directly without object:
如果GMLwriter::write不依赖于任何 GMLwriter 状态（访问 的任何成员GMLwriter），则可以将其设为静态成员函数。然后你可以不用对象直接调用它：
class GMLwriter
{
public:
static bool write(const char *fn, MyList<User*>& my_vec, vector<string>edges);
^^^^
};
then you could call:
那么你可以调用：
GMLwriter::write(argv[3], Users, edges);
回答by Pubby
GMLwriteris not an object, it's a class type.
GMLwriter不是一个对象，它是一个类类型。
Calling member functions requires an object instance, ie:
调用成员函数需要一个对象实例，即：
GMLwriter foo;
foo.write(argv[3], Users, edges);
Although there's a good chance you intended the function to be free or static:
尽管您很可能希望该功能是免费的或静态的：
class GMLwriter{
public:
// static member functions don't use an object of the class,
// they are just free functions inside the class scope
static bool write(const char *fn, MyList<User*>& my_vec, vector<string>edges);
};
// ...
GMLwriter::write(argv[3], Users, edges);
or
或者
bool write(const char *fn, MyList<User*>& my_vec, vector<string>edges);
// ...
write(argv[3], Users, edges);
回答by Ronaldo Nazarea
You might be trying to call / create a static method, to be
您可能正在尝试调用/创建一个静态方法，以便
In this case, you might want to precede your declaration with a 'static' modifier.
在这种情况下，您可能希望在声明之前使用 'static' 修饰符。
