lib/string-number.x

Numeric parsing from canonical byte strings.

Advanced and interop API

String

String.try_double

int String.try_double(String str, double *out)

Parses all of str as a floating-point number, writing out. Returns 1 and writes out on success; returns 0 and leaves out untouched on failure.

The whole string must be the number, on the same terms as String.try_long: leading and trailing whitespace are allowed and any other unconsumed character is a failure, so 1.5junk does not parse.

It accepts what C’s strtod accepts, including hex-float literals such as 0x1p4 and the inf and nan spellings. A value that overflows or underflows double fails. It does not know the 0o and 0b prefixes that the integer parser adds, so 0b101 fails instead of yielding the leading zero.

Source: lib/string-number.x:86

String.try_long

int String.try_long(String str, long *out)

Parses all of str as an integer, writing it through out. Returns 1 and writes out on success; returns 0 and leaves out untouched on failure.

The whole string must be the number. Leading and trailing whitespace are allowed and any other unconsumed character is a failure, so 42 succeeds and 42junk does not. A + or - sign is accepted, and the radix prefixes 0x, 0o, 0b, and C’s leading-zero octal are recognized. A value outside the range of long fails.

long value = 0;
printf("%d %ld\n", %" -0b101 ".try_long(&value), value);
printf("%d\n", %"42junk".try_long(&value));

Source: lib/string-number.x:39

Design notes

The readers require a complete parse and leave caller output untouched on failure. Parsing allocates no storage.