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16.7 Standards Versus Existing Practice

Historically, awk has converted any nonnumeric-looking string to the numeric value zero, when required. Furthermore, the original definition of the language and the original POSIX standards specified that awk only understands decimal numbers (base 10), and not octal (base 8) or hexadecimal numbers (base 16).

Changes in the language of the 2001 and 2004 POSIX standards can be interpreted to imply that awk should support additional features. These features are:

The first problem is that both of these are clear changes to historical practice:

The second problem is that the gawk maintainer feels that this interpretation of the standard, which required a certain amount of “language lawyering” to arrive at in the first place, was not even intended by the standard developers. In other words, “We see how you got where you are, but we don’t think that that’s where you want to be.”

Recognizing these issues, but attempting to provide compatibility with the earlier versions of the standard, the 2008 POSIX standard added explicit wording to allow, but not require, that awk support hexadecimal floating-point values and special values for “not a number” and infinity.

Although the gawk maintainer continues to feel that providing those features is inadvisable, nevertheless, on systems that support IEEE floating point, it seems reasonable to provide some way to support NaN and infinity values. The solution implemented in gawk is as follows:

Besides handling input, gawk also needs to print “correct” values on output when a value is either NaN or infinity. Starting with version 4.2.2, for such values gawk prints one of the four strings just described: ‘+inf’, ‘-inf’, ‘+nan’, or ‘-nan’. Similarly, in POSIX mode, gawk prints the result of the system’s C printf() function using the %g format string for the value, whatever that may be.

NOTE: The sign used for NaN values can vary! The result depends upon both the underlying system architecture and the underlying library used to format NaN values. In particular, it’s possible to get different results for the same function call depending upon whether or not gawk is running in MPFR mode (-M) or not. Caveat Emptor!


Footnotes

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