Win10
TDM-GCC 4.9.2 64bit
只知道extern的粗浅概念,有错纠正
如果a档案的一个变量前面前置字有extern 那该变量就是在其他档案有定义,在link阶段才
会把extern变量的位址提供给a(是这样说吗?),编译时a只会知道这个变量的名称跟型态而
已
范例:
https://goo.gl/rBdTXw 我把const前置词先拿掉 先不考虑const的问题
file1.c:
unsigned char data1[] =
{
0x65, 0xF0, 0xA8, 0x5F, 0x5F,
0x5F, 0x5F, 0x31, 0x32, 0x2E,
0x31, 0xF1, 0x63, 0x4D, 0x43,
0x52, 0x45, 0x41, 0x54, 0x45,
0x44, 0x20, 0x42, 0x59, 0x3A,
0x20, 0x69, 0x73, 0x70, 0x56,
};
unsigned int data1_size = sizeof(data1) / sizeof(data1[0]);
unsigned int data1_version = 1;
main.c:
struct Data_Info
{
unsigned char * data_ptr;
unsigned int data_size;
unsigned int data_version;
};
extern unsigned char data1[];
extern unsigned int data1_size;
extern unsigned int data1_version;
static struct Data_Info Data_Info_Table[] =
{
{ data1, data1_size, data1_version},
};
int main(void)
{
return 0;
}
[Error] initializer element is not constant
[Error] (near initialization for 'Data_Info_Table[0].data_size')
[Error] (near initialization for 'Data_Info_Table[0].data_version')
下面的回应是说The problem is that the compiler doesn't know the value to place
into the data_size and data_version members of the field.
ok,但是我不太确定结构的第一个成员指标变量为什么没有问题?
是因为它是位址? 在compiler阶段会跟编译器讲data1有定义在某处,所以link阶段就会得
link到? 是不是跟引用外部function的概念一样?
谢谢