OpenCV -- Function to grab frame - opencv

Question

I'm trying to create a function that gives the frame at the moment the function is called. So when i call the function, it should give the picture of the object that is in front of the camera at the moment the function is called.
I have been trying for hours, but i can't succeed. Anyone?
main file:
#include "camera.h"
#include <iostream>
#include <unistd.h>
int main(int argc, const char *argv[])
{
Camera cam;
cam.setVideoSource(0);
cv::Mat image;
cv::Mat image2;
cam.openCamera();
cam.grabFrame(image); // grap first frame
sleep(5); // wait 5 seconds
cam.grabFrame(image2); // capture seconds frame
cv::namedWindow("1",CV_WINDOW_KEEPRATIO);
cv::imshow("1",image);
cv::namedWindow("2",CV_WINDOW_KEEPRATIO);
cv::imshow("2",image2);
cv::waitKey();
return 0;
}
camera.h file
#include <iostream>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/core/core.hpp>
class Camera{
private:
int videoSource; //video source
cv::VideoCapture cap; //capture of camera
public:
//constructor default videoSourceNumber
Camera() : videoSource(0) {};
//Setter: videoSourceNumber
void setVideoSource(int sourceNumber){
videoSource = sourceNumber;
}
//function OPEN CAMERA
//opens the video capture
//returns true if successfull
bool openCamera() {
cap.open(videoSource);
if (!cap.isOpened()){
std::cout << "---- Error ----" << std::endl;
return false;
}
return true;
}
//function GRAB FRAME
//grabs the frame of the video capture
//returns true if successfull
bool grabFrame(cv::Mat& cameraFrame){
cap >> cameraFrame;
if (cameraFrame.empty()){
std::cout << "---- Error ----" << std::endl;
return false;
}
return true;
}
};

Answer 1

A somewhat unsatisfying solution:
//function GRAB FRAME
//grabs the frame of the video capture
//returns true if successfull
bool grabFrame(cv::Mat& cameraFrame){
int attempts = 0;
do {
cap >> cameraFrame;
attempts++;
} while (cameraFrame.empty() && attempts < 10);
if (cameraFrame.empty()){
std::cout << "---- Error ----" << std::endl;
return false;
}
return true;
}
I also played with this for a while and could not find a solution. My instinct was to give the camera more "warm-up" time before asking for the first frame. A sleep of 10 seconds seems to do so reliably, but that is not acceptable. If I don't give it any sleep before the first grabFrame() call, the while loop I added only seems to run twice.
Credit to: https://stackoverflow.com/a/9285151/2518451