Menu
How do you read the second line of this macro? What does (type *)0 mean in this context?
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)->member ) *__mptr = (ptr); \
(type *)( (char *)__mptr - offsetof(type,member) );})
517
A macro is an automated input sequence that imitates keystrokes or mouse actions. A macro is typically used to replace a repetitive series of keyboard and mouse actions and used often in spreadsheets and word processing applications like MS Excel and MS Word. The file extension of a macro is commonly . MAC.
In C, the macro is used to define any constant value or any variable with its value in the entire program that will be replaced by this macro name, where macro contains the set of code that will be called when the macro name is used in the program.
The double-number-sign or token-pasting operator (##), which is sometimes called the merging or combining operator, is used in both object-like and function-like macros. It permits separate tokens to be joined into a single token, and therefore, can't be the first or last token in the macro definition.
You're finding the type of ((type *)0)->member. It's not actually dereferencing the pointer (that would be madness, I tell you. Madness!)
It's a weirdness of C. Maybe it would make more sense if they wrote typeof(type.member) but sadly that is not allowed.
139
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
