访问typedef映射结构中的成员？

Question

My question should be simple and I've spent that last few hours trying to get an answer to it by figuring it out on my own (and google-ing) answers and getting nowhere.

I've got the following in my header file:

Window.hpp

typedef struct {
    SDL_Window* window = 0;
    const char* title = 0;
    int width;
    int height;
    int flags;
} m_windowStruct;

typedef std::map<std::string, m_windowStruct> m_windowMap;

m_windowMap windowMap; /* <-- Made this accessible */

and in my source file I've the following code:

Window.cpp

bool Window::createWindow(std::string id, const char* title, int width, int height, int flags) {
    m_windowMap* windowMap;
    m_windowStruct windowData;

    windowData.window = SDL_CreateWindow("insert window creation info here");

    if (!windowData.window) {
        windowData.title = title;
        windowData.width = width;
        windowData.height = height;
        windowData.flags = flags;
        windowMap->insert(m_windowMap::value_type(id, &windowData));
        SDL_LogInfo(INFO, "Window creation successful");
        return true;
    }
    else {
        return false;
    }
};

Which works all fine and dandy... The problem I'm having is accessing the mapped struct members after.

For example if I want the instance of the primary window I'd want the following function:

/* Returns the window instance from the mapped struct */
SDL_Window* Window::getWindow(std::string id) {
    m_windowMap::const_iterator keyValuePair = windowMap.find(id); /* <-- New error: Error: expression must have a class type */

    if (keyValuePair == windowMap.end()) { /* <-- same error as just above */
        return 0;
    }

    return keyValuePair->second.window; /* <-- Same error as just above */
};

I cannot for the life of me figure out how to access the second window member so that I can then give it to my renderer!

Any ideas?

Answer 1

I guess you want the windowMap being a global variable which is accessible across multiple source files (ie, .cpp). Here are the changes you need to make,

In header file, replace the last line with extern m_windowMap* windowMap; . This makes variable accessible to all source files that include the header.

In your main function (or anywhere appropriate), add this line to initialize the map windowMap = new m_windowMap();

Remove m_windowMap* windowMap; in the Window::createWindow function, otherwise the re-declaration creates a new local m_windowMap and the rest of the function makes no effect to the global windowMap .

Lastly, since the global windowMap is a pointer, change .find() and .end() to ->find() and ->end() in the getWindow function.

Answer 2

If the windowMap is indeed a class member of Window , it is actually easier and cleaner.

From the code you originally posted, remove m_windowMap* windowMap; in the Window::createWindow function. Otherwise the insert goes to this newly created local map. Also, change ->insert to .insert as you did not declare windowMap as an pointer in the header.