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问题描述
我在Linux内核中有以下代码:
I have this code in linux kernel:
#define task_cred_xxx(task, xxx)
({
__typeof__(((struct cred *)NULL)->xxx) ___val;
rcu_read_lock();
___val = __task_cred((task))->xxx;
rcu_read_unlock();
___val;
})
我以前从未见过这样定义的宏，这是否意味着task_cred_xxx(task，xxx)返回___ val?
I never saw macro defined like this before, does that mean this is task_cred_xxx(task, xxx) returns ___val?
谢谢！
推荐答案
正确.它将返回___val.但是，像这样的块表达式是GNU扩展，实际上并不是C标准的一部分.
Correct. It will return ___val. However, block expressions like these are a GNU extension and isn't actually part of the C standard.
http://www.toofishes.net/blog/gcc-compound -statement-expressions/
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