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Comments on Macro to verify that an expression has no side effects at compile time
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Macro to verify that an expression has no side effects at compile time
I'd like to implement a macro strnul():
#define strnul(s) (s + strlen(s))
But that expands and evaluates s twice. I'd like to avoid that.
I could do (using GNU extensions)
#define strnul(s) \
({ \
auto s_ = s; \
s_ + strlen(s_);\
})
However, this adds some other problem: a local variable named s_.
This local variable must have a name different from whatever users of this function may pass as argument, as otherwise we'd have auto s_ = s_;, which can't work.
But I have reasons to pass an argument called s_, so I'd like to find a way to entirely avoid the variable. If possible, an alternative would be to do
#define strnul(s) \
({ \
static_assert(!has_side_effects(s)); \
s + strlen(s); \
})
Is it possible to somehow do this in C? Even if the solution would require using compiler extensions, I'd be interested in finding a solution.
2 comment threads