谁能解释一下“->”是如何在#define 中实现的

Question

I'm working on a reference design with this line as a #define

#define MEDIA_EXT_STATE "\"adv7611 12-004c\":1 -> \"40080000.tpg\":0[%d]"

The sprintf function uses it which is then passed to the media_parse_setup_links() function.

sprintf(media_formats, MEDIA_EXT_STATE, 1);
ret = media_parse_setup_links(media, media_formats);

Answer 1

The macro defines MEDIA_EXT_STATE as a string literal, similar as

#define FOOBAR "foo -> bar"

defines FOOBAR as the string literal "foo -> bar" . Maybe you got confused by the escaped " , but thats just like with ordinary string literals:

std::cout << "\"123";

prints "123 .

To know what is the meaning of the -> in the string, you'd have to look into the implementation of media_parse_setup_links or read the documentation.

Answer 2

It simply translates to:

 sprintf(media_formats, "\"adv7611 12-004c\":1 -> \"40080000.tpg\":0[%d]", 1);

There is no pointer operation, as it is just part of the string.

When removing the quotes it becomes more obvious:

 sprintf(media_formats, "'adv7611 12-004c':1 -> '40080000.tpg':0[%d]", 1);

Answer 3

can anyone explain how the “->” is implemented

It's just text. It is "implemented" the same way as this:

std::string example = "->";