CodeVisionAVR
3.2 Comments
The character string "/*" marks the beginning of a comment. The end of the comment is marked with "*/".
Example:
/* This is a comment */ /* This is a
multiple line comment */
One-line comments may be also defined by using the string "//". Example:
// This is also a comment
Nested comments are not allowed.
© 1998-2007 HP InfoTech S.R.L. |
Page 71 |
CodeVisionAVR
3.3 Reserved Keywords
Following is a list of keywords reserved by the compiler. These can not be used as identifier names.
break bit case char const continue default defined do double eeprom else enum extern flash float for funcused goto
if inline int interrupt long register return short signed sizeof sfrb sfrw static struct switch typedef union unsigned void volatile while
© 1998-2007 HP InfoTech S.R.L. |
Page 72 |
CodeVisionAVR
3.4 Identifiers
An identifier is the name you give to a variable, function, label or other object.
An identifier can contain letters (A...Z, a...z) and digits (0...9), as well as the underscore character (_). However an identifier can only start with a letter or an underscore.
Case is significant; i.e. variable1 is not the same as Variable1. Identifiers can have up to 32 characters.
3.5 Data Types
The following table lists all the data types supported by the CodeVisionAVR C compiler, their range of possible values and their size:
Type |
Size (Bits) |
Range |
bit |
1 |
0 , 1 |
char |
8 |
-128 to 127 |
unsigned char |
8 |
0 to 255 |
signed char |
8 |
-128 to 127 |
int |
16 |
-32768 to 32767 |
short int |
16 |
-32768 to 32767 |
unsigned int |
16 |
0 to 65535 |
signed int |
16 |
-32768 to 32767 |
long int |
32 |
-2147483648 to 2147483647 |
unsigned long int |
32 |
0 to 4294967295 |
signed long int |
32 |
-2147483648 to 2147483647 |
float |
32 |
±1.175e-38 to ±3.402e38 |
double |
32 |
±1.175e-38 to ±3.402e38 |
The bit data type is supported only for global variables.
If the Project|Configure|C Compiler|Code Generation|char is unsigned option is checked or
#pragma uchar+ is used, then char has by default the range 0..255.
© 1998-2007 HP InfoTech S.R.L. |
Page 73 |
CodeVisionAVR
3.6 Constants
Integer or long integer constants may be written in decimal form (e.g. 1234), in binary form with 0b prefix (e.g. 0b101001), in hexadecimal form with 0x prefix (e.g. 0xff) or in octal form with 0-prefix (e.g. 0777).
Unsigned integer constants may have the suffix U (e.g. 10000U). Long integer constants may have the suffix L (e.g. 99L).
Unsigned long integer constants may have the suffix UL (e.g. 99UL). Floating point constants may have the suffix F (e.g. 1.234F).
Character constants must be enclosed in single quotation marks. E.g. 'a'.
String constants must be enclosed in double quotation marks. E.g. "Hello world".
If you place a string between quotes as a function parameter, this string will automatically be considered as constant and will be placed in FLASH memory.
Example:
/ * this function displays a string located in SRAM */ void display_ram(char *s) {
/* ....... */
}
/ * this function displays a string located in FLASH */ void display_flash(char flash *s) {
/* ....... */
}
void main(void) {
/* this will not work !!! */
/* because the function addresses the string as */
/* it is located in SRAM, but the string "Hello world" */ /* is constant and is placed in FLASH */ display_ram("Hello world");
/* this will work !!! */
/* the function addresses the string as it is located in FLASH */ display_flash("Hello world");
}
Constant can be grouped in arrays, which can have up to 8 dimensions.
Constants are stored in FLASH memory, to specify this you must use the flash or const keywords. Constant expressions are automatically evaluated during compilation.
Example:
flash int |
integer_constant=1234+5; |
flash char |
char_constant=’a’; |
flash long |
long_int_constant1=99L; |
flash long |
long_int_constant2=0x10000000; |
flash int |
integer_array1[]={1,2,3}; |
/* The first two elements will be 1 and 2, the rest will be 0 */
flash int integer_array2[10]={1,2};
flash int multidim_array[2][3]={{1,2,3},{4,5,6}};
flash char string_constant1[]=”This is a string constant”; const char string_constant2[]=”This is also a string constant”;
Constants can’t be declared inside functions.
© 1998-2007 HP InfoTech S.R.L. Page 74