问题
After perusing the web and messing around myself, I can't seem to convert a void*'s target (which is a string) to a std::string. I've tried using sprintf(buffer, "%p", *((int *)point)); as recommended by this page to get to a C string, but to no avail. And sadly, yes, I have to use a void*, as that's what SDL uses in their USEREVENT struct.
The code I'm using to fill the Userevent, for those interested, is:
std::string filename = "ResumeButton.png";
SDL_Event button_press;
button_press.type = BUTTON_PRESS;
button_press.user.data1 = &filename;
SDL_PushEvent(&button_press);
Any ideas?
EDIT: Thanks for all the responses, I just needed to cast the void* to a std::string*. Silly me. Thank you guys so much!
回答1:
You just need to dynamically allocate it (because it probably needs to outlive the scope you're using it in), then cast it back and forth:
// Cast a dynamically allocated string to 'void*'.
void *vp = static_cast<void*>(new std::string("it's easy to break stuff like this!"));
// Then, in the function that's using the UserEvent:
// Cast it back to a string pointer.
std::string *sp = static_cast<std::string*>(vp);
// You could use 'sp' directly, or this, which does a copy.
std::string s = *sp;
// Don't forget to destroy the memory that you've allocated.
delete sp;
回答2:
Based on your comment "What I meant was to convert what the void* is pointing to (which is a string) into a string."
Assuming you have this:
std::string str = ...;
void *ptr = &str;
You can just cast back to the string:
std::string *pstr = static_cast<std::string *>(ptr);
Note that it is on you to verify that ptr actually points to a std::string. If you are mistaken and it points to something else, this will cause undefined behavior.
回答3:
If you trying to format the address as text you can use a stringstream:
std::stringstream strm;
strm << ptr;
std::string str = strm.str();
// str will now have something like "0x80004567"
If that's not what you are interested in, please clarify your question.
回答4:
If the void is a const char*, then you can just call the std::string constructor with it, i.e.
const char* cakes = something;
std::string lols = std::string(cakes);
来源：https://stackoverflow.com/questions/3076968/converting-a-void-to-a-stdstring