How to produce a NaN float in c?

Question

float f = (float)\'a\';
if(f < 0){ 
}   
else if(f == 0){ 
}   
else if(f > 0){ 
}   
else{
    printf(\"NaN\\n\");                                                     


        

Answer 1

From the GNU GCC manual math.h defines macros that allow you to explicitly set a variable to infinity or NaN. Since this is a part of C99 you can use the following macros with other c99 compliant compilers i hope.

— Macro: float INFINITY An expression representing positive infinity. It is equal to the value produced by mathematical operations like 1.0 / 0.0. -INFINITY represents negative infinity.

You can test whether a floating-point value is infinite by comparing it to this macro. However, this is not recommended; you should use the isfinite macro instead. See Floating Point Classes.

This macro was introduced in the ISO C99 standard.

— Macro: float NAN An expression representing a value which is “not a number”. This macro is a GNU extension, available only on machines that support the “not a number” value—that is to say, on all machines that support IEEE floating point.

You can use ‘#ifdef NAN’ to test whether the machine supports NaN. (Of course, you must arrange for GNU extensions to be visible, such as by defining _GNU_SOURCE, and then you must include math.h.)

for further information you can see here: http://www.gnu.org/s/hello/manual/libc/Infinity-and-NaN.html