c语言中@的意思是什么？

2024-11-19 06:26:26

推荐回答（5个）

回答1：

@可以这样用
Declaration = [@

|@"

"]
[= ];
Global Variable Address Modifier (@address)
You can assign global variables to specific addresses with the global variable address modifier. These variables are called 'absolute variables'. They are useful for accessing memory mapped I/O ports and have the following syntax:

Declaration = [@

|@"

"]
[= ];
is the type specifier, e.g., int, char

is the identifier of the global object, e.g., i, glob

is the absolute address of the object, e.g., 0xff04, 0x00+8

is the value to which the global variable is initialized.

A segment is created for each global object specified with an absolute address. This address must not be inside any address range in the SECTIONS entries of the link parameter file. Otherwise, there would be a linker error (overlapping segments). If the specified address has a size greater than that used for addressing the default data page, pointers pointing to this global variable must be "__far". An alternate way to assign global variables to specific addresses is (Listing 8.8).

Listing 8.8 Assigning global variables to specific addresses

#pragma DATA_SEG [__SHORT_SEG]
setting the PLACEMENT section in the linker parameter file. An older method of accomplishing this is shown in Listing 8.9.

Listing 8.9 Another means of assigning global variables to specific addresses

INTO READ_ONLY

;
Listing 8.10 is a correct and incorrect example of using the global variable address modifier and Listing 8.11 is a possible PRM file that corresponds with example Listing.

Listing 8.10 Using the global variable address modifier
//看这意思,就是把int型变量glob地址从0x0500开始,并把值10初始化时放在0x0500
int glob @0x0500 = 10; // OK, global variable "glob" is
// at 0x0500, initialized with 10
void g() @0x40c0; // error (the object is a function)

void f() {
int i @0x40cc; // error (the object is a local variable)
}

回答2：

@ 只能放在字符，字符串或注解行里使用。
例如： char s[]="b@c"; // @ in string
它不是运算符，也不能作为标识符的一部分。

volatile 变量是易变化变量，编译器不得对它作优化处理。

回答3：

#define  AP_CODE_ADDR_START  0
#define  AP_CODE_LEN         0x14000
const uint16_t FixData@(AP_CODE_ADDR_START + AP_CODE_LEN-2) = 0x55aa;
/************以下解释***************/
定义uint16_t类型的FixData变量，并且指定其初始地址，并且变量赋值为0x55aa。

回答4：

回答5：

表示不显示@后面的命令