Question

I am working on my little touchscreen code for an embedded microcontroller. I had my code working using functions. But now I want to make it into a class. I get an error:

expression must have class type.

And I don’t know what the problem is. I googled my problem and no clear solution was found. Here’s my code:

main.cpp

#include "screen.h"
#include "mbed.h"
#include "stdio.h"

screen test();

    int main(void)
    {

        while (1)
        {
        test.button(50,70,100,50,"button1"); // line where the compiler sees an error
        }  
    }

screen.h

class screen{

public:

        screen();

        void init();
        void button(int, int, int, int, string);

private:
        int runningstatus; // 0 = stopped // 1 = failure // 2 = running
        point p;


};

screen.cpp

#include "screen.h"

touch_tft TFT(p20,p18,p17,p16,p5, p6, p7, p8, p15,"TFT"); // x+,x-,y+,y-,mosi, miso, sclk, cs, reset


screen::screen(){


}

void screen::init()
{
        TFT.claim(stdout);          // send stdout to the TFT display 
    TFT.background(Black);    // set background to black
    TFT.foreground(White);    // set chars to white
    TFT.cls();                // clear the screen
    TFT.set_orientation(3);
    TFT.set_font((unsigned char*) Arial24x23);
        TFT.locate(60, 100);
}

void screen::button(int x0, int y0, int length, int height, string caption)
{
        TFT.rect(x0     ,y0     ,x0+length      ,y0+height,     LightGrey);
        TFT.rect(x0-1   ,y0-1   ,x0+length+1    ,y0+height+1, LightGrey);
        TFT.fillrect(x0-2,y0-2 ,x0+length-1 ,y0+height-1, Navy);

        TFT.locate(x0+10, y0+10);

        TFT.background(Navy);   
        TFT.printf("%s", caption);
}

Can someone tell me what the problem with this code is. Its driving me totaly nuts!

Answer 1

You need to change: screen test(); to screen test;. As it is right now, you’re declaring a function named test that returns a screen, not defining an object named test of type screen.

This is quite well known as C++’s “most vexing parse” (a good term to search for if you want more information).