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Explains parseHex initialization quirk.

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This commit is contained in:
Grzegorz Adam Hankiewicz
2013-07-16 01:11:20 +02:00
parent b5811cc73c
commit 67cea2b9b5
1 changed files with 26 additions and 2 deletions
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28
lib/pure/parseutils.nim
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@@ -27,8 +27,24 @@ proc toLower(c: char): char {.inline.} =
proc parseHex*(s: string, number: var int, start = 0): int {.
rtl, extern: "npuParseHex", noSideEffect.} =
## parses a hexadecimal number and stores its value in ``number``. Returns
## the number of the parsed characters or 0 in case of an error.
## Parses a hexadecimal number and stores its value in ``number``.
##
## Returns the number of the parsed characters or 0 in case of an error. This
## proc is sensitive to the already existing value of ``number`` and will
## likely not do what you want unless you make sure ``number`` is zero. You
## can use this feature to *chain* calls, though the result int will quickly
## overflow. Example:
##
## .. code-block:: nimrod
## var value = 0
## discard parseHex("0x38", value)
## assert value == 56
## discard parseHex("0x34", value)
## assert value == 56 * 256 + 52
## value = -1
## discard parseHex("0x38", value)
## assert value == -200
##
var i = start
var foundDigit = false
if s[i] == '0' and (s[i+1] == 'x' or s[i+1] == 'X'): inc(i, 2)
@@ -383,6 +399,14 @@ iterator interpolatedFragments*(s: string): tuple[kind: TInterpolatedKind,
when isMainModule:
for k, v in interpolatedFragments("$test{} $this is ${an{ example}} "):
echo "(", k, ", \"", v, "\")"
var value = 0
discard parseHex("0x38", value)
assert value == 56
discard parseHex("0x34", value)
assert value == 56 * 256 + 52
value = -1
discard parseHex("0x38", value)
assert value == -200
{.pop.}