Loading image from memory - c++

Question

According to the documentation, one can load an sf::Texture three different ways: from file, from stream, from memory. I think I need the latter, but I'm not even sure about that. And if I do, I can't figure out how to use it.
I have a method, which, given an url to work with, needs to return an sf::Sprite. I'm successfully downloading the binary data, and storing it in a string (since Http::Response::getBody() returns that). I know for a fact, that this is the right data, because if I write and save it to a file, I can view the image. I don't want a file however, I just need the image displayed.
Here is the function:
sf::Sprite Downloader::GetPicture(const std::string &url)
{
sf::Http http;
std::string host = url.substr(0, url.find("net/")+4 );
std::string uri = url.substr(url.find("net/")+4, url.size());
http.setHost(host);
request.setUri(uri);
response = http.sendRequest(request);
std::string data = response.getBody();
//THIS IS WRONG
sf::Texture texture;
texture.loadFromMemory((void*)data, sizeof(data));
return sf::Sprite(texture);
/* THIS WORKS, BUT I DON'T WANT TO SAVE, REOPEN, THEN DELETE AT THE END
std::ofstream fileout("test.jpg", std::ios::binary);
fileout << data;
fileout.close();
*/
}
Here is loadFromMemory's signature for the lazy (the void* confuses me, that's probably the problem).
Also, this might be a completely wrong way to do it; maybe extending sf::InputStream, and using loadFromStream?
The problem is, returned sf::Sprite has 0×0 dimension and 0 size, that's how I know it's wrong.

Answer 1

There are two mistakes in your code. One was spotted by Casey, that is you should use texture.loadFromMemory(data.data(), data.length()).
The problem with texture.loadFromMemory((void*)data, sizeof(data)); is that you will load some garbage and not necessarily the picture data; you will load the other attributes of the string (like an integer for the length, and maybe a pointer for the data itself).
The other one is related to the white square problem: you return a sprite but not the texture. After the function returns, the texture is destroyed and the sprite will display only a white rectangle instead.
You could do something like:
sf::Texture dlpicture(std::string host, std::string uri)
{
sf::Http http(host);
sf::Http::Request request(uri);
auto response = http.sendRequest(request);
auto data = response.getBody();
sf::Texture text;
text.loadFromMemory(data.data(), data.length());
return text;
}
which you can try with sf::Texture texture = dlpicture("www.sfml-dev.org", "download/goodies/sfml-logo-small.png");.
SFML indeed support jpg format but not all its variants. Progressive jpg is not supported for example. You'll have to use another format.