Re^2: [OT(C)] float parameter treated as double by callee -- but it fails with FFI

Exactly, in TIFF.xs double is simply cast to float, no issues with that. My confusion was about line 337, where double is expected as argument. But, what I just found in plain Wikipedia:

Another consideration is the default argument promotions applied to the unnamed arguments. A float will automatically be promoted to a double. Likewise, arguments of types narrower than an int will be promoted to int or unsigned int. The function receiving the unnamed arguments must expect the promoted type.

That answers my question about libtiff code. And, perhaps implicitly, addresses the question about FFI: for variadic functions, promoted args types must be specified (i.e. not float, but double). OK, now I'm educated:)

Comment on Re^2: [OT(C)] float parameter treated as double by callee -- but it fails with FFI

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Re^3: [OT(C)] float parameter treated as double by callee -- but it fails with FFI by syphilis (Archbishop) on Jun 30, 2021 at 00:30 UTC
A float will automatically be promoted to a double I wasn't aware of this, either. I've eventually located this info in K&R (2nd Edition) in section A7 - "A7.3.2 Function Calls". Thanks for spreading the education !! Cheers, Rob	[reply]
Re^3: [OT(C)] float parameter treated as double by callee -- but it fails with FFI by ikegami (Patriarch) on Jul 01, 2021 at 23:10 UTC
That's why there's no `printf` length modifier for ~~`char`~~, `float` or `double`. `signed char c = 123; int i = 123; float f = 123; double d = 123; printf("%d\n", i); // ok printf("%d\n", c); // ok, even though %d expects int. printf("%f\n", d); // ok printf("%f\n", f); // ok, even though %f expects double.` [download] (Not sure why there's one for `short` since they are guaranteed to be no larger than an `int` and `unsigned int` respectively.) Seeking work! You can reach me at ikegami@adaelis.com	[reply] [d/l] [select]
Re^4: [OT(C)] float parameter treated as double by callee -- but it fails with FFI by ikegami (Patriarch) on Jul 01, 2021 at 23:42 UTC
There is one for `char` (`hh`). The reason it and the one for `short` (`h`) exists is purely for symmetry with `scanf` (which needs to know the type of object at the provided address). Seeking work! You can reach me at ikegami@adaelis.com	[reply] [d/l] [select]


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