C ++类Typedef Struct未命名类型

Question

I'm trying to make use of typedef structs inside of my C++ program. I started writing the following code until I received an error when trying to add a method to my class that returns a template typedef struct pointer.

StructSource.h

template <typename T>
class StructSource {
public:
    struct TestStruct{
        T value;
    };
};

User.h

#include "StructSource.h"

class User {
    public:
        typedef StructSource<int>::TestStruct IntStruct;

        IntStruct *getIntStruct();

};

User.cpp

#include "User.h"

IntStruct *User::getIntStruct() {
    return 0;
}

This gives the following error when compiling with GCC.

User.cpp:3:1: error: 'IntStruct' does not name a type

I'm at a loss to explain why this is the case. What type information am I missing?

Answer 1

"User" is also a "namespace" (scope, actually, as most commenters point out - "namespace" was for a quick answer) here, so you have to use

User::IntStruct *User::getIntStruct() {
    return 0;
}

Answer 2

You need:

User::IntStruct *User::getIntStruct() { ... }

IntStruct is defined inside the User scope, but the return value of the function is not in scope. there is a discussion of these scoping issues here .

Answer 3

Since IntStruct was defined within the class, you must use the class name to reference it, except within the class code where it is part of the default name search path.

User::IntStruct *User::getIntStruct() {

This is not the same as a namespace, even though the syntax is identical.