What is assignment makes pointer from integer without a cast

NunoLava1998 · Post by **NunoLava1998** » Wed Dec 07, 2016 4:40 am

I am putting a lot of functions into my OS (i recently added farpeekl, outb, inb, lidt and kbdhandler).

However, in my keyboard handler, a warning occurs (-Wextra and -Wall):

Code: Select all

kernel.c: In function 'kbdhandler':
kernel.c:199:6: warning: assignment makes pointer from integer without a cast [enabled by default]
  key = kbdus[scancode];
      ^

This is to set the key to the translated scancode-key result.

Here's my kbdus and kbdhandler function, inb and terminal_writestring are exactly as shown in the OSDev wikia. (headers not included):

Code: Select all

unsigned char kbdus[128] =
{
    0,  27, '1', '2', '3', '4', '5', '6', '7', '8',	/* 9 */
  '9', '0', '-', '=', '\b',	/* Backspace */
  '\t',			/* Tab */
  'q', 'w', 'e', 'r',	/* 19 */
  't', 'y', 'u', 'i', 'o', 'p', '[', ']', '\n',	/* Enter key */
    0,			/* 29   - Control */
  'a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l', ';',	/* 39 */
 '\'', '`',   0,		/* Left shift */
 '\\', 'z', 'x', 'c', 'v', 'b', 'n',			/* 49 */
  'm', ',', '.', '/',   0,				/* Right shift */
  '*',
    0,	/* Alt */
  ' ',	/* Space bar */
    0,	/* Caps lock */
    0,	/* 59 - F1 key ... > */
    0,   0,   0,   0,   0,   0,   0,   0,
    0,	/* < ... F10 */
    0,	/* 69 - Num lock*/
    0,	/* Scroll Lock */
    0,	/* Home key */
    0,	/* Up Arrow */
    0,	/* Page Up */
  '-',
    0,	/* Left Arrow */
    0,
    0,	/* Right Arrow */
  '+',
    0,	/* 79 - End key*/
    0,	/* Down Arrow */
    0,	/* Page Down */
    0,	/* Insert Key */
    0,	/* Delete Key */
    0,   0,   0,
    0,	/* F11 Key */
    0,	/* F12 Key */
    0,	/* All other keys are undefined */
};
void kbdhandler()
{
	unsigned char scancode;
	const char *key;
	scancode = inb(0x60);
	key = kbdus[scancode];
	terminal_writestring(key);
}

It worked fine with putchar but i am switching to writestring since instead of putting the first letter and continuing it filled the screen with whatever the keyboard was sending, which is not what i want.

How do i fix this? I can't seem to find a solution on the internet.

Kevin · Post by **Kevin** » Wed Dec 07, 2016 4:53 am

key is a const char* (i.e. a pointer type) whereas kbdus[scancode] is an unsigned char (i.e. an integer type). These are fundamentally different types, so the compiler thinks chances are that the assignment is wrong. And the compiler is right, kbdus[scancode] doesn't contain integers that make sense as a pointer.

If you want a string, you need to create one. That is, you need some memory where you can put the character and a '\0' byte. Maybe in this case a local char array of size 2 is what you want.

NunoLava1998 · Post by **NunoLava1998** » Wed Dec 07, 2016 4:59 am

Kevin wrote:key is a const char* (i.e. a pointer type) whereas kbdus[scancode] is an unsigned char (i.e. an integer type). These are fundamentally different types, so the compiler thinks chances are that the assignment is wrong. And the compiler is right, kbdus[scancode] doesn't contain integers that make sense as a pointer.

If you want a string, you need to create one. That is, you need some memory where you can put the character and a '\0' byte. Maybe in this case a local char array of size 2 is what you want.

How do i do it? If i try to change kbdus from unsigned char to const char *, this happens:

Code: Select all

kernel.c:46:5: warning: initialization makes pointer from integer without a cast [enabled by default]
     0,  27, '1', '2', '3', '4', '5', '6', '7', '8', /* 9 */
     ^
kernel.c:46:5: warning: (near initialization for 'kbdus[1]') [enabled by default]
kernel.c:46:5: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:46:5: warning: (near initialization for 'kbdus[2]') [enabled by default]
kernel.c:46:5: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:46:5: warning: (near initialization for 'kbdus[3]') [enabled by default]
kernel.c:46:5: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:46:5: warning: (near initialization for 'kbdus[4]') [enabled by default]
kernel.c:46:5: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:46:5: warning: (near initialization for 'kbdus[5]') [enabled by default]
kernel.c:46:5: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:46:5: warning: (near initialization for 'kbdus[6]') [enabled by default]
kernel.c:46:5: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:46:5: warning: (near initialization for 'kbdus[7]') [enabled by default]
kernel.c:46:5: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:46:5: warning: (near initialization for 'kbdus[8]') [enabled by default]
kernel.c:46:5: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:46:5: warning: (near initialization for 'kbdus[9]') [enabled by default]
kernel.c:47:3: warning: initialization makes pointer from integer without a cast [enabled by default]
   '9', '0', '-', '=', '\b', /* Backspace */
   ^
kernel.c:47:3: warning: (near initialization for 'kbdus[10]') [enabled by default]
kernel.c:47:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:47:3: warning: (near initialization for 'kbdus[11]') [enabled by default]
kernel.c:47:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:47:3: warning: (near initialization for 'kbdus[12]') [enabled by default]
kernel.c:47:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:47:3: warning: (near initialization for 'kbdus[13]') [enabled by default]
kernel.c:47:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:47:3: warning: (near initialization for 'kbdus[14]') [enabled by default]
kernel.c:48:3: warning: initialization makes pointer from integer without a cast [enabled by default]
   '\t',   /* Tab */
   ^
kernel.c:48:3: warning: (near initialization for 'kbdus[15]') [enabled by default]
kernel.c:49:3: warning: initialization makes pointer from integer without a cast [enabled by default]
   'q', 'w', 'e', 'r', /* 19 */
   ^
kernel.c:49:3: warning: (near initialization for 'kbdus[16]') [enabled by default]
kernel.c:49:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:49:3: warning: (near initialization for 'kbdus[17]') [enabled by default]
kernel.c:49:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:49:3: warning: (near initialization for 'kbdus[18]') [enabled by default]
kernel.c:49:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:49:3: warning: (near initialization for 'kbdus[19]') [enabled by default]
kernel.c:50:3: warning: initialization makes pointer from integer without a cast [enabled by default]
   't', 'y', 'u', 'i', 'o', 'p', '[', ']', '\n', /* Enter key */
   ^
kernel.c:50:3: warning: (near initialization for 'kbdus[20]') [enabled by default]
kernel.c:50:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:50:3: warning: (near initialization for 'kbdus[21]') [enabled by default]
kernel.c:50:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:50:3: warning: (near initialization for 'kbdus[22]') [enabled by default]
kernel.c:50:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:50:3: warning: (near initialization for 'kbdus[23]') [enabled by default]
kernel.c:50:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:50:3: warning: (near initialization for 'kbdus[24]') [enabled by default]
kernel.c:50:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:50:3: warning: (near initialization for 'kbdus[25]') [enabled by default]
kernel.c:50:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:50:3: warning: (near initialization for 'kbdus[26]') [enabled by default]
kernel.c:50:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:50:3: warning: (near initialization for 'kbdus[27]') [enabled by default]
kernel.c:50:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:50:3: warning: (near initialization for 'kbdus[28]') [enabled by default]
kernel.c:52:3: warning: initialization makes pointer from integer without a cast [enabled by default]
   'a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l', ';', /* 39 */
   ^
kernel.c:52:3: warning: (near initialization for 'kbdus[30]') [enabled by default]
kernel.c:52:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:52:3: warning: (near initialization for 'kbdus[31]') [enabled by default]
kernel.c:52:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:52:3: warning: (near initialization for 'kbdus[32]') [enabled by default]
kernel.c:52:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:52:3: warning: (near initialization for 'kbdus[33]') [enabled by default]
kernel.c:52:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:52:3: warning: (near initialization for 'kbdus[34]') [enabled by default]
kernel.c:52:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:52:3: warning: (near initialization for 'kbdus[35]') [enabled by default]
kernel.c:52:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:52:3: warning: (near initialization for 'kbdus[36]') [enabled by default]
kernel.c:52:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:52:3: warning: (near initialization for 'kbdus[37]') [enabled by default]
kernel.c:52:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:52:3: warning: (near initialization for 'kbdus[38]') [enabled by default]
kernel.c:52:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:52:3: warning: (near initialization for 'kbdus[39]') [enabled by default]
kernel.c:53:2: warning: initialization makes pointer from integer without a cast [enabled by default]
  '\'', '`',   0,  /* Left shift */
  ^
kernel.c:53:2: warning: (near initialization for 'kbdus[40]') [enabled by default]
kernel.c:53:2: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:53:2: warning: (near initialization for 'kbdus[41]') [enabled by default]
kernel.c:54:2: warning: initialization makes pointer from integer without a cast [enabled by default]
  '\\', 'z', 'x', 'c', 'v', 'b', 'n',   /* 49 */
  ^
kernel.c:54:2: warning: (near initialization for 'kbdus[43]') [enabled by default]
kernel.c:54:2: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:54:2: warning: (near initialization for 'kbdus[44]') [enabled by default]
kernel.c:54:2: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:54:2: warning: (near initialization for 'kbdus[45]') [enabled by default]
kernel.c:54:2: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:54:2: warning: (near initialization for 'kbdus[46]') [enabled by default]
kernel.c:54:2: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:54:2: warning: (near initialization for 'kbdus[47]') [enabled by default]
kernel.c:54:2: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:54:2: warning: (near initialization for 'kbdus[48]') [enabled by default]
kernel.c:54:2: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:54:2: warning: (near initialization for 'kbdus[49]') [enabled by default]
kernel.c:55:3: warning: initialization makes pointer from integer without a cast [enabled by default]
   'm', ',', '.', '/',   0,    /* Right shift */
   ^
kernel.c:55:3: warning: (near initialization for 'kbdus[50]') [enabled by default]
kernel.c:55:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:55:3: warning: (near initialization for 'kbdus[51]') [enabled by default]
kernel.c:55:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:55:3: warning: (near initialization for 'kbdus[52]') [enabled by default]
kernel.c:55:3: warning: initialization makes pointer from integer without a cast [enabled by default]
kernel.c:55:3: warning: (near initialization for 'kbdus[53]') [enabled by default]
kernel.c:56:3: warning: initialization makes pointer from integer without a cast [enabled by default]
   '*',
   ^
kernel.c:56:3: warning: (near initialization for 'kbdus[55]') [enabled by default]
kernel.c:58:3: warning: initialization makes pointer from integer without a cast [enabled by default]
   ' ', /* Space bar */
   ^
kernel.c:58:3: warning: (near initialization for 'kbdus[57]') [enabled by default]
kernel.c:68:3: warning: initialization makes pointer from integer without a cast [enabled by default]
   '-',
   ^
kernel.c:68:3: warning: (near initialization for 'kbdus[74]') [enabled by default]
kernel.c:72:3: warning: initialization makes pointer from integer without a cast [enabled by default]
   '+',
   ^
kernel.c:72:3: warning: (near initialization for 'kbdus[78]') [enabled by default]

And terminal_writestring only accepts const char *, so i can't change "key"'s type.

Ycep · Post by **Ycep** » Wed Dec 07, 2016 5:14 am

Please, learn C already...
This is probably what you wanted:

Code: Select all

void kbdhandler()
{
   unsigned char scancode, key;
   scancode = inb(0x60);
   key = kbdus[scancode];
   terminal_writestring(key);
}

Making mistakes like this one would lead you nowhere in operating system development, as in algorithmic programming, general programming, game programming, etc.

NunoLava1998 · Post by **NunoLava1998** » Wed Dec 07, 2016 5:25 am

Lukand wrote:Please, learn C already...
This is probably what you wanted:
Code: Select all
void kbdhandler()
{
   unsigned char scancode, key;
   scancode = inb(0x60);
   key = kbdus[scancode];
   terminal_writestring(key);
}
Making mistakes like this one would lead you nowhere in operating system development, as in algorithmic programming, general programming, game programming, etc.

Except terminal_writestring expects a const char *. Therefore...

Code: Select all

kernel.c: In function 'kbdhandler':
kernel.c:199:4: warning: passing argument 1 of 'terminal_writestring' makes pointer from integer without a cast [enabled by default]
    terminal_writestring(key);
    ^
kernel.c:152:6: note: expected 'const char *' but argument is of type 'unsigned char'
 void terminal_writestring(const char* data) {

iansjack · Post by **iansjack** » Wed Dec 07, 2016 5:44 am

Why are you using a string writing function to write a character? Just program a function that writes a single character to the screen.

NunoLava1998 · Post by **NunoLava1998** » Wed Dec 07, 2016 6:29 am

iansjack wrote:Why are you using a string writing function to write a character? Just program a function that writes a single character to the screen.

Beacuse terminal_write won't work and terminal_putchar puts the letter that is pressed into every single slot of the screen for some reason.
Also, terminal_writechar with 1 note and 1 warning like you said brings... here, have the bin file, test it on qemu.

here's an image demonstrating what happens if you move your mouse and hold something that keeps the "S " screen
http://i.imgur.com/iS9IUmz.png ((mod edit: Turned oversized image into a link))

iansjack · Post by **iansjack** » Wed Dec 07, 2016 6:38 am

It's kind of you to offer me the chance to debug your code but I'm afraid I must decline the offer.

NunoLava1998 · Post by **NunoLava1998** » Wed Dec 07, 2016 6:46 am

iansjack wrote:It's kind of you to offer me the chance to debug your code but I'm afraid I must decline the offer.

It's not to debug my code, it's beacuse i don't know how to explain it so i figured out you could see it.

Solar · Post by **Solar** » Wed Dec 07, 2016 7:16 am

You might want to check the Required Knowledge page in the Wiki. Kernel level programming is a very poor environment to practice your programming skills. You should be proficient in whatever programming language you chose, before you start with OSDev.

User space has much superior debugging tools and features, errors don't require a reboot, examples are easier for others to reproduce, plus several other advantages. There are specialized websites for questions regarding user-space programming, like stackoverflow.com.

Kevin · Post by **Kevin** » Wed Dec 07, 2016 7:59 am

NunoLava1998 wrote:Beacuse terminal_write won't work and terminal_putchar puts the letter that is pressed into every single slot of the screen for some reason.

Then fix that.

How do i do it? If i try to change kbdus from unsigned char to const char *, this happens

This is not what I told you to do.

Octacone · Post by **Octacone** » Wed Dec 07, 2016 11:22 pm

This topic is really scary. How are you expecting your "print string" function to work if your "print character" function is not working... You CANNOT print a character using "print string" function, you need to use "print character" function. I would suggest you fixing your C before fixing anything else

onlyonemac · Post by **onlyonemac** » Thu Dec 08, 2016 2:25 am

Because I don't feel like reading through all your code, I'll answer the question in the thread title:

"assignment makes pointer from integer without a cast" means that you're assigning an integer data type (char, short, int, long) to a variable that's supposed to hold a pointer (void*, char*, any_type_of_your_choice_t*). Sometimes this is a valid operation - say you're calculating a pointer from integer values - but in that case you should cast the value to the correct pointer type. More likely, you've made a mistake and are either a) storing your pointers in integer variables or b) storing your integers in pointer variables. Note that arrays are treated as pointers to the type that they hold, so if you declare an array "int my_array[128]", then my_array is actually a pointer to int (i.e. "int*"), whereas my_array[n] is a value of type int. Also note the difference between "char" and "char*", and between single and double quotes - the former holds a single character while the latter holds an array (string) of characters, and single quotes can be used to specify a single character literal (of type "char") and double quotes to specify a string literal (of type "char*").

NunoLava1998 · Post by **NunoLava1998** » Thu Dec 08, 2016 5:37 am

I realized this is beacuse i put the thing in a loop. I tried to implement io_wait and put it in the keyboard_handler, nothin'. I need to know how to halt until a key is pressed.

iansjack · Post by **iansjack** » Thu Dec 08, 2016 5:51 am

NunoLava1998 wrote:I need to know how to halt until a key is pressed.

That's why your keyboard handler should be interrupt driven.

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What is assignment makes pointer from integer without a cast

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