C99 Floating Hexadecimal I/O Support in libc

Summary of Change

The strtod, printf, and scanf families of functions are enhanced to handle floating hexadecimal input and output.

Details of Change

APIs printf and scanf are enhanced to handle the new format specifiers 'a' and 'A' for floating hexadecimal input and output as specified in C99. The API strtod() is enhanced to accept floating hexadecimal sequences as specified in C99. These changes are extensions to existing functionality.

Impact

No impact.

Compatibility

The new scanf and strtod functions could affect the behavior of an existing program which depends on the rejection of input that the updated functions accept as a floating hexadecimal number. For example, the output of the following program:

#include <stdio.h>
int main() { 
     const char* input = "0x1p0z"; 
     float x; 
     char c; 
     sscanf(input, "%e%c", &x, &c); 
     printf("x = %g\n", x); 
     printf("c = %c\n", c);

changes from:

x = 0 

c = x

to:

x = 1 

c = z

Performance

There is no change in performance.

Obsolescence

Not applicable.

Documentation

The manpages for printf(3S), scanf(3S) and strtod(3C) have been updated to reflect this enhancement.