digitalmars.D.learn - extern(C) bool function type?
- Charles Hixson (8/8) Sep 26 2013 Does anyone know:
- bearophile (10/17) Sep 26 2013 A D bool is a C99 uint8_t that has values just 0 or 1.
- Charles Hixson (21/37) Sep 26 2013 It's a library function, that claims to return bool, but is a C
- bearophile (5/11) Sep 26 2013 Take a look at this entertaining page:
- Charles Hixson (6/17) Sep 26 2013 I'd forgotten about:
- Jacob Carlborg (6/12) Sep 26 2013 In general 0 is false and all other integers are true. So if the
Does anyone know: If an extern(c) function is defined as returning a bool, does D handle the conversion automatically into true and false? Should it be defined as returning an int? On a 64 bit machine? Does this depend on the compiler used to compile the library? int32_t? int_64_t? Is this portable or non-portable? -- Charles Hixson
Sep 26 2013
Charles Hixson:Does anyone know: If an extern(c) function is defined as returning a bool, does D handle the conversion automatically into true and false? Should it be defined as returning an int? On a 64 bit machine? Does this depend on the compiler used to compile the library? int32_t? int_64_t? Is this portable or non-portable?A D bool is a C99 uint8_t that has values just 0 or 1. If your uint8_t contains a value x > 1, in many cases this works, but some D code relying on the standard values of a D boolean breaks (like when you sum bool values in D, to count the true ones). D doesn't handle those conversions beside the narrowing or extension of bit-width lengths. Bye, bearophile
Sep 26 2013
On 09/26/2013 12:19 PM, bearophile wrote:Charles Hixson:It's a library function, that claims to return bool, but is a C function. My suspicion is that the proper way to handle this is to say that it returns an int, or possibly an int32_t, i.e. to declare is as not returning a bool, even though the library says that that's what it returns. But my computer is a 64 bit machine, and the code was compiled awhile ago, so I suspect it may really be returning an int32_t. The problem is that if I guess wrong this will not dependably cause a problem. (I had a hope that D would say "O, it's a C routine returning a bool, so I know how to deal with that", but that wasn't really my expectation.) Yeah, if I were defining the function, I'd define it in a way that I know how to handle properly. But I'm not, and the interface is for either C or C++. I can choose between those two. So... if C returns an int64_t and I declare it as an int32_t, will this cause problems? What about if C returns an int32_t and I declare it as an int64_t? Or *is* there a good way to handle this? (I think that there's an error code I could interrogate if I need to just ignore the result...but I don't know if I can do this in all cases.) -- Charles HixsonDoes anyone know: If an extern(c) function is defined as returning a bool, does D handle the conversion automatically into true and false? Should it be defined as returning an int? On a 64 bit machine? Does this depend on the compiler used to compile the library? int32_t? int_64_t? Is this portable or non-portable?A D bool is a C99 uint8_t that has values just 0 or 1. If your uint8_t contains a value x > 1, in many cases this works, but some D code relying on the standard values of a D boolean breaks (like when you sum bool values in D, to count the true ones). D doesn't handle those conversions beside the narrowing or extension of bit-width lengths. Bye, bearophile
Sep 26 2013
Charles Hixson:So... if C returns an int64_t and I declare it as an int32_t, will this cause problems? What about if C returns an int32_t and I declare it as an int64_t? Or *is* there a good way to handle this? (I think that there's an error code I could interrogate if I need to just ignore the result...but I don't know if I can do this in all cases.)Take a look at this entertaining page: http://dlang.org/phobos/std_stdint.html Bye, bearophile
Sep 26 2013
I'd forgotten about: int_least8_t I guess that's what I should use. On 09/26/2013 03:06 PM, bearophile wrote:Charles Hixson:-- Charles HixsonSo... if C returns an int64_t and I declare it as an int32_t, will this cause problems? What about if C returns an int32_t and I declare it as an int64_t? Or *is* there a good way to handle this? (I think that there's an error code I could interrogate if I need to just ignore the result...but I don't know if I can do this in all cases.)Take a look at this entertaining page: http://dlang.org/phobos/std_stdint.html Bye, bearophile
Sep 26 2013
On 2013-09-26 20:56, Charles Hixson wrote:Does anyone know: If an extern(c) function is defined as returning a bool, does D handle the conversion automatically into true and false? Should it be defined as returning an int? On a 64 bit machine? Does this depend on the compiler used to compile the library? int32_t? int_64_t? Is this portable or non-portable?In general 0 is false and all other integers are true. So if the function returns 0 or 1 it will automatically work for true and false as well. -- /Jacob Carlborg
Sep 26 2013