I'm following a tutorial on how to make an operating system in C. Everything works in the tutorial, no error messages, nothing, while I get the error specified in the title. Is making variables from the struct "Char" global even an option?

#include "print.h"

const static size_t NUM_COLS = 80;
const static size_t NUM_ROWS = 25;

struct Char {
    uint8_t character;
    uint8_t color;
};

struct Char* buffer = (struct Char*) 0xb8000;
size_t col = 0;
size_t row = 0;
uint8_t color = PRINT_COLOR_WHITE | PRINT_COLOR_BLACK << 4;

void clear_row(size_t row) {
    struct Char empty = (struct Char) {
        character: ' ',
        color: color,
    };

    for (size_t col = 0; col < NUM_COLS; col  ) {
        buffer[col   NUM_COLS * row] = empty;
    }
}

void print_clear() {
    for (size_t i = 0; i < NUM_ROWS; i  ) {
        clear_row(i);
    }
}

void print_newline() {
    col = 0;

    if (row < NUM_ROWS - 1) {
        row  ;
        return;
    }

    for (size_t row = 1; row < NUM_ROWS; row  ) {
        for (size_t col = 0; col < NUM_COLS; col  ) {
            struct Char character = buffer[col   NUM_COLS * row];
            buffer[col   NUM_COLS * (row - 1)] = character;
        }
    }

    clear_row(NUM_COLS - 1);
}

void print_char(char character) {
    if (character == '\n') {
        print_newline();
        return;
    }

    if (col > NUM_COLS) {
        print_newline();
    }

    buffer[col   NUM_COLS * row] = (struct Char) {
        character: (uint8_t) character,
        color: color,
    };

    col  ;
}

void print_str(char* str) {
    for (size_t i = 0; 1; i  ) {
        char character = (uint8_t) str[i];

        if (character == '\0') {
            return;
        }

        print_char(character);
    }
}

void print_set_color(uint8_t foreground, uint8_t background) {
    color = foreground   (background << 4);
}

I am fairly new to C, so I might not know even easier things than this. Thanks in advance!

I also apologize if this question has been asked already, I couldn't find the answer anywhere.

CodePudding user response：

struct Char empty = (struct Char) {
    character: ' ',
    color: color,
};

That is not how you initialize a struct object in C. You need to do something like

struct Char empty = { ' ', color };

or

struct Char empty = { .character = ' ', .color = color };

or

struct Char empty;

empty.character = ' ';
empty.color = color;

Also, C doesn't like trailing commas in initializers or enumerations - the compiler will complain about a missing expression in that case.

CodePudding user response：

For making a struct variable/object global in C:

//m.c - the content of the global struct variable will be printed in this translational unit

#include<stdio.h>

struct node
{
    int i;
    char c;
};

extern struct node no;
void fun();

int main()
{
    fun();
    printf("i = %d, c= %c\n",no.i,no.c);
    return 0;
}

in the other translational unit where the global struct variable is declared and defined:

//n.c
struct node
{
    int i;
    char c;
}no;

void fun()
{
    no.i=89;
    no.c='S';
}

The struct needs to be present in both the translational units, so it is better to declare that in a header and then include that header wherever required.