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Make scanf read back [+][-]Inf and NaN



LabWindows/CVI 9.0.1's implementation of <stdio.h> *scanf and <stdlib.h> strtod functions appears not to support reading back "NaN", "Inf", "+Inf" or "-Inf" values, although printf() can generate them. May I suggest to add functionality like described below.


Practical use would be that it's easier to propagate "invalid measurement" through strings if strto*() and *scanf() understand all classes of strings that *printf() family functions will generate.


This suggestion is in alignment with ISO 9899:1999 (withdrawn) and its successor ISO 9899:2011, i. e. C99 and C11. Note that there is a "stronger" suggestion to implement all of the C11 standard library in the idea exchange already, which - if implemented - would subsume this suggestion, but as the bare minimum, I'd certainly appreciate seeing this in CVI 2012.


Demo code:


 printf("%g\n", -NotANumber());
 printf("%+g\n", PositiveInfinity());
 printf("%g\n", NegativeInfinity());
 double x = 0; int i;
 i = sscanf("NaN", "%lf", &x); printf("i=%d, x=%g\n", i, x);
 i = sscanf("Inf", "%lf", &x); printf("i=%d, x=%g\n", i, x);
 errno = 0; x = strtod("NaN", NULL); printf("x=%g, errno=%d\n", x, errno);


Desired result:





 i=1, x=NaN

 i=1, x=Inf

 x=NaN, errno=0


Actual result: we see that printf supports NaN/Inf, but scanf and strtod do not:


 i=0, x=0
 i=0, x=0
 x=0, errno=0


Thank you.


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Status changed to: Under Consideration