错误:可变大小的对象可能未被初始化?
问题描述:
我想提出一个键盘驱动程序我的OSDev OS和我在我的kbd.c一个问题:错误:可变大小的对象可能未被初始化?
kbd.c: In function 'scancoderec':
kbd.c:56:2: error: variable-sized object may not be initialized
register int (ScanCode[strlen(ValEAX)-8]) = 0x00; /* Remove last 8 bits from the value we gathered from EAX to get AH and make that the scancode. */
这里是包含的代码失败行的功能:
int scancoderec() {
__asm__ volatile("movl $0, %eax"); /* Moving 00 to EAX. */
__asm__ volatile("int $0x16 "); /*int 0x16 */
register int ValEAX asm("eax"); /* Let's get eax */
register int (ScanCode[strlen(ValEAX)-8]) = 0x00; /* Remove last 8 bits from the value we gathered from EAX to get AH and make that the scancode. */
}
为什么这是否发生?
编辑:我仍然有这个“ax”是未定义的,这次,在另一个函数中。
kbd.c:65:27: error: 'ax' undeclared (first use in this function)
register int Key = kbdus[ax];
扫描码功能和信息getKey功能的代码:
unsigned short scancodeget()
{
unsigned char ax = 0; /* int 0x16, AH=0 is get keystroke */
__asm__ __volatile__ ("int $0x16\n\t"
: "+a"(ax));
ax = ax >> 8; /* Shift top 8 bits of ax to lower 8 bits */
/* ax now is the scancode returned by BIOS */
return (unsigned short)ax; /* Return the lower 8 bits */
}
int getkey() { /*This could be used as a keyboard driver. */
scancoderec(); /*Get our scancode! */
int Key = kbdus[ax]; /*Use our kbdus array which i copied from a website since i seriously don't want to make an gigantic array */
}
答
很难说出您要实现的目标。此例程返回从BIOS interrupt 16h/AH=0h返回的原始扫描代码。它使用GCC extended assembler template使用input/output constraint将值为0的AX传递到汇编程序模板,并在之后检索AX中的值。扫描码位于ax
变量的高8位,因此我们将其右移8位。
#include <stdint.h>
uint8_t getchar_scancode()
{
uint16_t ax = 0; /* int 0x16, AH=0 is get keystroke */
__asm__ __volatile__ ("int $0x16\n\t"
: "+a"(ax));
/* +a is an input and output constraint using EAX register */
/* The contents of the 'ax' variable will be transferred */
/* into EAX register upon entry, and the value of EAX register */
/* will be transferred into variable 'ax' when finished */
ax = ax >> 8; /* Shift top 8 bits of ax to lower 8 bits */
/* ax now is the scancode returned by BIOS */
return (uint8_t)ax; /* Return the lower 8 bits */
}
如果没有stdint.h
也可用来定义uint16_t
你可以用unsigned short
取代它与unsigned char
取代uint8_t
。
如果您需要扫描码转换为可以使用的附加功能,以提供该功能的ASCII字符:
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 */
};
uint8_t getchar()
{
return (kbdus[getchar_scancode()]);
}
BIOS中断不会在保护模式下运行,并可能会故障的机器。 INT 16h/AH = 0仅适用于实模式。
答
错误消息是清楚。您不可以初始化一个可变长度数组。写,而不是
register int (ScanCode[strlen(ValEAX)-8]);
ScanCode[0] = 0x00;
或者你可以使用标准的C函数memset
,在头<string.h>
宣布向量的所有元素设置为0x00
。
例如
memset(ScanCode, 0x00, sizeof(ScanCode));
答
线
register int (ScanCode[strlen(ValEAX)-8]) = 0x00;
声明一个VLA和试图初始化它,这是不允许的。将其更改为:
// Declare
int size = strlen(ValEAX)-8
register int ScanCode[size];
// Set values.
for (int i = 0; i < size; ++i)
{
ScanCode[i] = 0x00;
}
编译器认为你正在声明一个名为'ScanCode'的数组。坦率地说,我不知道你要在代码中做什么。 – user3386109
评论说:“从值中删除最后8位...” - >看起来像“删除最后8个字节...” – chux
嗯,如果'strlen(ValEAX) chux